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![Paul Gortmaker](/assets/img/avatar_default.png)
The Kconfig currently controlling compilation of tree.c is: init/Kconfig:config TREE_RCU init/Kconfig: bool ...and update.c and sync.c are "obj-y" meaning that none are ever built as a module by anyone. Since MODULE_ALIAS is a no-op for non-modular code, we can remove them from these files. We leave moduleparam.h behind since the files instantiate some boot time configuration parameters with module_param() still. Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
898 lines
28 KiB
C
898 lines
28 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, you can access it online at
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* http://www.gnu.org/licenses/gpl-2.0.html.
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*
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* Copyright IBM Corporation, 2001
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*
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* Authors: Dipankar Sarma <dipankar@in.ibm.com>
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* Manfred Spraul <manfred@colorfullife.com>
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*
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* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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* Papers:
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* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
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* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* http://lse.sourceforge.net/locking/rcupdate.html
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*
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*/
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/spinlock.h>
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#include <linux/smp.h>
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#include <linux/interrupt.h>
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#include <linux/sched.h>
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#include <linux/atomic.h>
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#include <linux/bitops.h>
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#include <linux/percpu.h>
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#include <linux/notifier.h>
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#include <linux/cpu.h>
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#include <linux/mutex.h>
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#include <linux/export.h>
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#include <linux/hardirq.h>
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#include <linux/delay.h>
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#include <linux/moduleparam.h>
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#include <linux/kthread.h>
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#include <linux/tick.h>
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#define CREATE_TRACE_POINTS
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#include "rcu.h"
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#ifdef MODULE_PARAM_PREFIX
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#undef MODULE_PARAM_PREFIX
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#endif
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#define MODULE_PARAM_PREFIX "rcupdate."
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#ifndef CONFIG_TINY_RCU
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module_param(rcu_expedited, int, 0);
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module_param(rcu_normal, int, 0);
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static int rcu_normal_after_boot;
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module_param(rcu_normal_after_boot, int, 0);
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#endif /* #ifndef CONFIG_TINY_RCU */
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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/**
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* rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
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*
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* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
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* RCU-sched read-side critical section. In absence of
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* CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
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* critical section unless it can prove otherwise. Note that disabling
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* of preemption (including disabling irqs) counts as an RCU-sched
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* read-side critical section. This is useful for debug checks in functions
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* that required that they be called within an RCU-sched read-side
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* critical section.
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*
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* Check debug_lockdep_rcu_enabled() to prevent false positives during boot
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* and while lockdep is disabled.
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*
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* Note that if the CPU is in the idle loop from an RCU point of
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* view (ie: that we are in the section between rcu_idle_enter() and
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* rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
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* did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
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* that are in such a section, considering these as in extended quiescent
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* state, so such a CPU is effectively never in an RCU read-side critical
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* section regardless of what RCU primitives it invokes. This state of
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* affairs is required --- we need to keep an RCU-free window in idle
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* where the CPU may possibly enter into low power mode. This way we can
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* notice an extended quiescent state to other CPUs that started a grace
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* period. Otherwise we would delay any grace period as long as we run in
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* the idle task.
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*
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* Similarly, we avoid claiming an SRCU read lock held if the current
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* CPU is offline.
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*/
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int rcu_read_lock_sched_held(void)
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{
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int lockdep_opinion = 0;
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if (!debug_lockdep_rcu_enabled())
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return 1;
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if (!rcu_is_watching())
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return 0;
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if (!rcu_lockdep_current_cpu_online())
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return 0;
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if (debug_locks)
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lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
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return lockdep_opinion || !preemptible();
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}
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EXPORT_SYMBOL(rcu_read_lock_sched_held);
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#endif
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#ifndef CONFIG_TINY_RCU
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/*
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* Should expedited grace-period primitives always fall back to their
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* non-expedited counterparts? Intended for use within RCU. Note
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* that if the user specifies both rcu_expedited and rcu_normal, then
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* rcu_normal wins.
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*/
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bool rcu_gp_is_normal(void)
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{
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return READ_ONCE(rcu_normal);
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}
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EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
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static atomic_t rcu_expedited_nesting =
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ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0);
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/*
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* Should normal grace-period primitives be expedited? Intended for
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* use within RCU. Note that this function takes the rcu_expedited
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* sysfs/boot variable into account as well as the rcu_expedite_gp()
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* nesting. So looping on rcu_unexpedite_gp() until rcu_gp_is_expedited()
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* returns false is a -really- bad idea.
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*/
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bool rcu_gp_is_expedited(void)
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{
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return rcu_expedited || atomic_read(&rcu_expedited_nesting);
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}
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EXPORT_SYMBOL_GPL(rcu_gp_is_expedited);
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/**
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* rcu_expedite_gp - Expedite future RCU grace periods
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*
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* After a call to this function, future calls to synchronize_rcu() and
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* friends act as the corresponding synchronize_rcu_expedited() function
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* had instead been called.
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*/
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void rcu_expedite_gp(void)
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{
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atomic_inc(&rcu_expedited_nesting);
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}
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EXPORT_SYMBOL_GPL(rcu_expedite_gp);
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/**
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* rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation
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*
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* Undo a prior call to rcu_expedite_gp(). If all prior calls to
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* rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(),
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* and if the rcu_expedited sysfs/boot parameter is not set, then all
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* subsequent calls to synchronize_rcu() and friends will return to
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* their normal non-expedited behavior.
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*/
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void rcu_unexpedite_gp(void)
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{
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atomic_dec(&rcu_expedited_nesting);
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}
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EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
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/*
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* Inform RCU of the end of the in-kernel boot sequence.
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*/
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void rcu_end_inkernel_boot(void)
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{
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if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT))
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rcu_unexpedite_gp();
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if (rcu_normal_after_boot)
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WRITE_ONCE(rcu_normal, 1);
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}
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#endif /* #ifndef CONFIG_TINY_RCU */
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#ifdef CONFIG_PREEMPT_RCU
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/*
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* Preemptible RCU implementation for rcu_read_lock().
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* Just increment ->rcu_read_lock_nesting, shared state will be updated
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* if we block.
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*/
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void __rcu_read_lock(void)
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{
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current->rcu_read_lock_nesting++;
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barrier(); /* critical section after entry code. */
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}
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EXPORT_SYMBOL_GPL(__rcu_read_lock);
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/*
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* Preemptible RCU implementation for rcu_read_unlock().
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* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
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* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
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* invoke rcu_read_unlock_special() to clean up after a context switch
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* in an RCU read-side critical section and other special cases.
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*/
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void __rcu_read_unlock(void)
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{
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struct task_struct *t = current;
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if (t->rcu_read_lock_nesting != 1) {
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--t->rcu_read_lock_nesting;
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} else {
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barrier(); /* critical section before exit code. */
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t->rcu_read_lock_nesting = INT_MIN;
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barrier(); /* assign before ->rcu_read_unlock_special load */
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if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
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rcu_read_unlock_special(t);
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barrier(); /* ->rcu_read_unlock_special load before assign */
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t->rcu_read_lock_nesting = 0;
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}
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#ifdef CONFIG_PROVE_LOCKING
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{
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int rrln = READ_ONCE(t->rcu_read_lock_nesting);
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WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
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}
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#endif /* #ifdef CONFIG_PROVE_LOCKING */
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}
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EXPORT_SYMBOL_GPL(__rcu_read_unlock);
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#endif /* #ifdef CONFIG_PREEMPT_RCU */
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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static struct lock_class_key rcu_lock_key;
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struct lockdep_map rcu_lock_map =
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STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
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EXPORT_SYMBOL_GPL(rcu_lock_map);
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static struct lock_class_key rcu_bh_lock_key;
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struct lockdep_map rcu_bh_lock_map =
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STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
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EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
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static struct lock_class_key rcu_sched_lock_key;
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struct lockdep_map rcu_sched_lock_map =
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STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
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EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
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static struct lock_class_key rcu_callback_key;
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struct lockdep_map rcu_callback_map =
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STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
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EXPORT_SYMBOL_GPL(rcu_callback_map);
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int notrace debug_lockdep_rcu_enabled(void)
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{
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return rcu_scheduler_active && debug_locks &&
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current->lockdep_recursion == 0;
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}
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EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
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/**
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* rcu_read_lock_held() - might we be in RCU read-side critical section?
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*
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* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
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* read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
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* this assumes we are in an RCU read-side critical section unless it can
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* prove otherwise. This is useful for debug checks in functions that
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* require that they be called within an RCU read-side critical section.
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*
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* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
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* and while lockdep is disabled.
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*
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* Note that rcu_read_lock() and the matching rcu_read_unlock() must
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* occur in the same context, for example, it is illegal to invoke
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* rcu_read_unlock() in process context if the matching rcu_read_lock()
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* was invoked from within an irq handler.
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*
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* Note that rcu_read_lock() is disallowed if the CPU is either idle or
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* offline from an RCU perspective, so check for those as well.
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*/
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int rcu_read_lock_held(void)
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{
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if (!debug_lockdep_rcu_enabled())
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return 1;
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if (!rcu_is_watching())
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return 0;
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if (!rcu_lockdep_current_cpu_online())
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return 0;
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return lock_is_held(&rcu_lock_map);
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}
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EXPORT_SYMBOL_GPL(rcu_read_lock_held);
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/**
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* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
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*
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* Check for bottom half being disabled, which covers both the
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* CONFIG_PROVE_RCU and not cases. Note that if someone uses
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* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
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* will show the situation. This is useful for debug checks in functions
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* that require that they be called within an RCU read-side critical
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* section.
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*
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* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
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*
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* Note that rcu_read_lock() is disallowed if the CPU is either idle or
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* offline from an RCU perspective, so check for those as well.
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*/
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int rcu_read_lock_bh_held(void)
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{
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if (!debug_lockdep_rcu_enabled())
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return 1;
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if (!rcu_is_watching())
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return 0;
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if (!rcu_lockdep_current_cpu_online())
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return 0;
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return in_softirq() || irqs_disabled();
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}
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EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
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#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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/**
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* wakeme_after_rcu() - Callback function to awaken a task after grace period
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* @head: Pointer to rcu_head member within rcu_synchronize structure
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*
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* Awaken the corresponding task now that a grace period has elapsed.
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*/
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void wakeme_after_rcu(struct rcu_head *head)
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{
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struct rcu_synchronize *rcu;
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rcu = container_of(head, struct rcu_synchronize, head);
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complete(&rcu->completion);
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}
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EXPORT_SYMBOL_GPL(wakeme_after_rcu);
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void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
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struct rcu_synchronize *rs_array)
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{
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int i;
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/* Initialize and register callbacks for each flavor specified. */
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for (i = 0; i < n; i++) {
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if (checktiny &&
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(crcu_array[i] == call_rcu ||
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crcu_array[i] == call_rcu_bh)) {
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might_sleep();
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continue;
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}
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init_rcu_head_on_stack(&rs_array[i].head);
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init_completion(&rs_array[i].completion);
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(crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
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}
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/* Wait for all callbacks to be invoked. */
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for (i = 0; i < n; i++) {
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if (checktiny &&
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(crcu_array[i] == call_rcu ||
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crcu_array[i] == call_rcu_bh))
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continue;
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wait_for_completion(&rs_array[i].completion);
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destroy_rcu_head_on_stack(&rs_array[i].head);
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}
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}
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EXPORT_SYMBOL_GPL(__wait_rcu_gp);
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#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
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void init_rcu_head(struct rcu_head *head)
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{
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debug_object_init(head, &rcuhead_debug_descr);
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}
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void destroy_rcu_head(struct rcu_head *head)
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{
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debug_object_free(head, &rcuhead_debug_descr);
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}
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static bool rcuhead_is_static_object(void *addr)
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{
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return true;
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}
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/**
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* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
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* @head: pointer to rcu_head structure to be initialized
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*
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* This function informs debugobjects of a new rcu_head structure that
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* has been allocated as an auto variable on the stack. This function
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* is not required for rcu_head structures that are statically defined or
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* that are dynamically allocated on the heap. This function has no
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* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
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*/
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void init_rcu_head_on_stack(struct rcu_head *head)
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{
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debug_object_init_on_stack(head, &rcuhead_debug_descr);
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}
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EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
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/**
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* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
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* @head: pointer to rcu_head structure to be initialized
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*
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* This function informs debugobjects that an on-stack rcu_head structure
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* is about to go out of scope. As with init_rcu_head_on_stack(), this
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* function is not required for rcu_head structures that are statically
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* defined or that are dynamically allocated on the heap. Also as with
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* init_rcu_head_on_stack(), this function has no effect for
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* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
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*/
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void destroy_rcu_head_on_stack(struct rcu_head *head)
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{
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debug_object_free(head, &rcuhead_debug_descr);
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}
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EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
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struct debug_obj_descr rcuhead_debug_descr = {
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.name = "rcu_head",
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.is_static_object = rcuhead_is_static_object,
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};
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EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
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#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
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void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
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unsigned long secs,
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unsigned long c_old, unsigned long c)
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{
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trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
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}
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EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
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#else
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#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
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do { } while (0)
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#endif
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#ifdef CONFIG_RCU_STALL_COMMON
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#ifdef CONFIG_PROVE_RCU
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#define RCU_STALL_DELAY_DELTA (5 * HZ)
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#else
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#define RCU_STALL_DELAY_DELTA 0
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#endif
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int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
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static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
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module_param(rcu_cpu_stall_suppress, int, 0644);
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module_param(rcu_cpu_stall_timeout, int, 0644);
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int rcu_jiffies_till_stall_check(void)
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{
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int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
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/*
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* Limit check must be consistent with the Kconfig limits
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* for CONFIG_RCU_CPU_STALL_TIMEOUT.
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*/
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if (till_stall_check < 3) {
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WRITE_ONCE(rcu_cpu_stall_timeout, 3);
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till_stall_check = 3;
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} else if (till_stall_check > 300) {
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WRITE_ONCE(rcu_cpu_stall_timeout, 300);
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till_stall_check = 300;
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}
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return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
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}
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void rcu_sysrq_start(void)
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{
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if (!rcu_cpu_stall_suppress)
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rcu_cpu_stall_suppress = 2;
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}
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void rcu_sysrq_end(void)
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{
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if (rcu_cpu_stall_suppress == 2)
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rcu_cpu_stall_suppress = 0;
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}
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static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
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{
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rcu_cpu_stall_suppress = 1;
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return NOTIFY_DONE;
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}
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static struct notifier_block rcu_panic_block = {
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.notifier_call = rcu_panic,
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};
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static int __init check_cpu_stall_init(void)
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{
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atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
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return 0;
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}
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early_initcall(check_cpu_stall_init);
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#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
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#ifdef CONFIG_TASKS_RCU
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/*
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* Simple variant of RCU whose quiescent states are voluntary context switch,
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* user-space execution, and idle. As such, grace periods can take one good
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* long time. There are no read-side primitives similar to rcu_read_lock()
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* and rcu_read_unlock() because this implementation is intended to get
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* the system into a safe state for some of the manipulations involved in
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* tracing and the like. Finally, this implementation does not support
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* high call_rcu_tasks() rates from multiple CPUs. If this is required,
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* per-CPU callback lists will be needed.
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*/
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/* Global list of callbacks and associated lock. */
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static struct rcu_head *rcu_tasks_cbs_head;
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static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
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static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
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static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
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/* Track exiting tasks in order to allow them to be waited for. */
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DEFINE_SRCU(tasks_rcu_exit_srcu);
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/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
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static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
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module_param(rcu_task_stall_timeout, int, 0644);
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static void rcu_spawn_tasks_kthread(void);
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static struct task_struct *rcu_tasks_kthread_ptr;
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/*
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* Post an RCU-tasks callback. First call must be from process context
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* after the scheduler if fully operational.
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*/
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void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
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{
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unsigned long flags;
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bool needwake;
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bool havetask = READ_ONCE(rcu_tasks_kthread_ptr);
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rhp->next = NULL;
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rhp->func = func;
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raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
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needwake = !rcu_tasks_cbs_head;
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*rcu_tasks_cbs_tail = rhp;
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rcu_tasks_cbs_tail = &rhp->next;
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raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
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/* We can't create the thread unless interrupts are enabled. */
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if ((needwake && havetask) ||
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(!havetask && !irqs_disabled_flags(flags))) {
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rcu_spawn_tasks_kthread();
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wake_up(&rcu_tasks_cbs_wq);
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}
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}
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EXPORT_SYMBOL_GPL(call_rcu_tasks);
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/**
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* synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
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*
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* Control will return to the caller some time after a full rcu-tasks
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* grace period has elapsed, in other words after all currently
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* executing rcu-tasks read-side critical sections have elapsed. These
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* read-side critical sections are delimited by calls to schedule(),
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* cond_resched_rcu_qs(), idle execution, userspace execution, calls
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* to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
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*
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* This is a very specialized primitive, intended only for a few uses in
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* tracing and other situations requiring manipulation of function
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* preambles and profiling hooks. The synchronize_rcu_tasks() function
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* is not (yet) intended for heavy use from multiple CPUs.
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*
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* Note that this guarantee implies further memory-ordering guarantees.
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* On systems with more than one CPU, when synchronize_rcu_tasks() returns,
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* each CPU is guaranteed to have executed a full memory barrier since the
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* end of its last RCU-tasks read-side critical section whose beginning
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* preceded the call to synchronize_rcu_tasks(). In addition, each CPU
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* having an RCU-tasks read-side critical section that extends beyond
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* the return from synchronize_rcu_tasks() is guaranteed to have executed
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* a full memory barrier after the beginning of synchronize_rcu_tasks()
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* and before the beginning of that RCU-tasks read-side critical section.
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* Note that these guarantees include CPUs that are offline, idle, or
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* executing in user mode, as well as CPUs that are executing in the kernel.
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*
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* Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
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* to its caller on CPU B, then both CPU A and CPU B are guaranteed
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* to have executed a full memory barrier during the execution of
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* synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
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* (but again only if the system has more than one CPU).
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*/
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void synchronize_rcu_tasks(void)
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{
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/* Complain if the scheduler has not started. */
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RCU_LOCKDEP_WARN(!rcu_scheduler_active,
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"synchronize_rcu_tasks called too soon");
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/* Wait for the grace period. */
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wait_rcu_gp(call_rcu_tasks);
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}
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EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
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/**
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* rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
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*
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* Although the current implementation is guaranteed to wait, it is not
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* obligated to, for example, if there are no pending callbacks.
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*/
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void rcu_barrier_tasks(void)
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{
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/* There is only one callback queue, so this is easy. ;-) */
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synchronize_rcu_tasks();
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}
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EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
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/* See if tasks are still holding out, complain if so. */
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static void check_holdout_task(struct task_struct *t,
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bool needreport, bool *firstreport)
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{
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int cpu;
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if (!READ_ONCE(t->rcu_tasks_holdout) ||
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t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
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!READ_ONCE(t->on_rq) ||
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(IS_ENABLED(CONFIG_NO_HZ_FULL) &&
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!is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
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WRITE_ONCE(t->rcu_tasks_holdout, false);
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list_del_init(&t->rcu_tasks_holdout_list);
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put_task_struct(t);
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return;
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}
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if (!needreport)
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return;
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if (*firstreport) {
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pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
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*firstreport = false;
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}
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cpu = task_cpu(t);
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pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
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t, ".I"[is_idle_task(t)],
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"N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
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t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
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t->rcu_tasks_idle_cpu, cpu);
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sched_show_task(t);
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}
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/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
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static int __noreturn rcu_tasks_kthread(void *arg)
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{
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unsigned long flags;
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struct task_struct *g, *t;
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unsigned long lastreport;
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struct rcu_head *list;
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struct rcu_head *next;
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LIST_HEAD(rcu_tasks_holdouts);
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/* Run on housekeeping CPUs by default. Sysadm can move if desired. */
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housekeeping_affine(current);
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/*
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* Each pass through the following loop makes one check for
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* newly arrived callbacks, and, if there are some, waits for
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* one RCU-tasks grace period and then invokes the callbacks.
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* This loop is terminated by the system going down. ;-)
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*/
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for (;;) {
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/* Pick up any new callbacks. */
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raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
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list = rcu_tasks_cbs_head;
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rcu_tasks_cbs_head = NULL;
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rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
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raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
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/* If there were none, wait a bit and start over. */
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if (!list) {
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wait_event_interruptible(rcu_tasks_cbs_wq,
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rcu_tasks_cbs_head);
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if (!rcu_tasks_cbs_head) {
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WARN_ON(signal_pending(current));
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schedule_timeout_interruptible(HZ/10);
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}
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continue;
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}
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/*
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* Wait for all pre-existing t->on_rq and t->nvcsw
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* transitions to complete. Invoking synchronize_sched()
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* suffices because all these transitions occur with
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* interrupts disabled. Without this synchronize_sched(),
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* a read-side critical section that started before the
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* grace period might be incorrectly seen as having started
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* after the grace period.
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*
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* This synchronize_sched() also dispenses with the
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* need for a memory barrier on the first store to
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* ->rcu_tasks_holdout, as it forces the store to happen
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* after the beginning of the grace period.
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*/
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synchronize_sched();
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/*
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* There were callbacks, so we need to wait for an
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* RCU-tasks grace period. Start off by scanning
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* the task list for tasks that are not already
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* voluntarily blocked. Mark these tasks and make
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* a list of them in rcu_tasks_holdouts.
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*/
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rcu_read_lock();
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for_each_process_thread(g, t) {
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if (t != current && READ_ONCE(t->on_rq) &&
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!is_idle_task(t)) {
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get_task_struct(t);
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t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
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WRITE_ONCE(t->rcu_tasks_holdout, true);
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list_add(&t->rcu_tasks_holdout_list,
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&rcu_tasks_holdouts);
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}
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}
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rcu_read_unlock();
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/*
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* Wait for tasks that are in the process of exiting.
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* This does only part of the job, ensuring that all
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* tasks that were previously exiting reach the point
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* where they have disabled preemption, allowing the
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* later synchronize_sched() to finish the job.
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*/
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synchronize_srcu(&tasks_rcu_exit_srcu);
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/*
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* Each pass through the following loop scans the list
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* of holdout tasks, removing any that are no longer
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* holdouts. When the list is empty, we are done.
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*/
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lastreport = jiffies;
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while (!list_empty(&rcu_tasks_holdouts)) {
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bool firstreport;
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bool needreport;
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int rtst;
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struct task_struct *t1;
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schedule_timeout_interruptible(HZ);
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rtst = READ_ONCE(rcu_task_stall_timeout);
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needreport = rtst > 0 &&
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time_after(jiffies, lastreport + rtst);
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if (needreport)
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lastreport = jiffies;
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firstreport = true;
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WARN_ON(signal_pending(current));
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list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
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rcu_tasks_holdout_list) {
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check_holdout_task(t, needreport, &firstreport);
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cond_resched();
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}
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}
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/*
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* Because ->on_rq and ->nvcsw are not guaranteed
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* to have a full memory barriers prior to them in the
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* schedule() path, memory reordering on other CPUs could
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* cause their RCU-tasks read-side critical sections to
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* extend past the end of the grace period. However,
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* because these ->nvcsw updates are carried out with
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* interrupts disabled, we can use synchronize_sched()
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* to force the needed ordering on all such CPUs.
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*
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* This synchronize_sched() also confines all
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* ->rcu_tasks_holdout accesses to be within the grace
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* period, avoiding the need for memory barriers for
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* ->rcu_tasks_holdout accesses.
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*
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* In addition, this synchronize_sched() waits for exiting
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* tasks to complete their final preempt_disable() region
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* of execution, cleaning up after the synchronize_srcu()
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* above.
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*/
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synchronize_sched();
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/* Invoke the callbacks. */
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while (list) {
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next = list->next;
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local_bh_disable();
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list->func(list);
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local_bh_enable();
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list = next;
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cond_resched();
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}
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schedule_timeout_uninterruptible(HZ/10);
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}
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}
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/* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */
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static void rcu_spawn_tasks_kthread(void)
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{
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static DEFINE_MUTEX(rcu_tasks_kthread_mutex);
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struct task_struct *t;
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if (READ_ONCE(rcu_tasks_kthread_ptr)) {
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smp_mb(); /* Ensure caller sees full kthread. */
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return;
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}
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mutex_lock(&rcu_tasks_kthread_mutex);
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if (rcu_tasks_kthread_ptr) {
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mutex_unlock(&rcu_tasks_kthread_mutex);
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return;
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}
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t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
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BUG_ON(IS_ERR(t));
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smp_mb(); /* Ensure others see full kthread. */
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WRITE_ONCE(rcu_tasks_kthread_ptr, t);
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mutex_unlock(&rcu_tasks_kthread_mutex);
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}
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#endif /* #ifdef CONFIG_TASKS_RCU */
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#ifdef CONFIG_PROVE_RCU
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/*
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* Early boot self test parameters, one for each flavor
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*/
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static bool rcu_self_test;
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static bool rcu_self_test_bh;
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static bool rcu_self_test_sched;
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module_param(rcu_self_test, bool, 0444);
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module_param(rcu_self_test_bh, bool, 0444);
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module_param(rcu_self_test_sched, bool, 0444);
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static int rcu_self_test_counter;
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static void test_callback(struct rcu_head *r)
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{
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rcu_self_test_counter++;
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pr_info("RCU test callback executed %d\n", rcu_self_test_counter);
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}
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static void early_boot_test_call_rcu(void)
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{
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static struct rcu_head head;
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call_rcu(&head, test_callback);
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}
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static void early_boot_test_call_rcu_bh(void)
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{
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static struct rcu_head head;
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call_rcu_bh(&head, test_callback);
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}
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static void early_boot_test_call_rcu_sched(void)
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{
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static struct rcu_head head;
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call_rcu_sched(&head, test_callback);
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}
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void rcu_early_boot_tests(void)
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{
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pr_info("Running RCU self tests\n");
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if (rcu_self_test)
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early_boot_test_call_rcu();
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if (rcu_self_test_bh)
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early_boot_test_call_rcu_bh();
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if (rcu_self_test_sched)
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early_boot_test_call_rcu_sched();
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}
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static int rcu_verify_early_boot_tests(void)
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{
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int ret = 0;
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int early_boot_test_counter = 0;
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if (rcu_self_test) {
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early_boot_test_counter++;
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rcu_barrier();
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}
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if (rcu_self_test_bh) {
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early_boot_test_counter++;
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rcu_barrier_bh();
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}
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if (rcu_self_test_sched) {
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early_boot_test_counter++;
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rcu_barrier_sched();
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}
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if (rcu_self_test_counter != early_boot_test_counter) {
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WARN_ON(1);
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ret = -1;
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}
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return ret;
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}
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late_initcall(rcu_verify_early_boot_tests);
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#else
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void rcu_early_boot_tests(void) {}
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#endif /* CONFIG_PROVE_RCU */
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