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![Linus Torvalds](/assets/img/avatar_default.png)
Pull locking updates from Ingo Molnar: "The main changes in this cycle were: - Continued user-access cleanups in the futex code. - percpu-rwsem rewrite that uses its own waitqueue and atomic_t instead of an embedded rwsem. This addresses a couple of weaknesses, but the primary motivation was complications on the -rt kernel. - Introduce raw lock nesting detection on lockdep (CONFIG_PROVE_RAW_LOCK_NESTING=y), document the raw_lock vs. normal lock differences. This too originates from -rt. - Reuse lockdep zapped chain_hlocks entries, to conserve RAM footprint on distro-ish kernels running into the "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!" depletion of the lockdep chain-entries pool. - Misc cleanups, smaller fixes and enhancements - see the changelog for details" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (55 commits) fs/buffer: Make BH_Uptodate_Lock bit_spin_lock a regular spinlock_t thermal/x86_pkg_temp: Make pkg_temp_lock a raw_spinlock_t Documentation/locking/locktypes: Minor copy editor fixes Documentation/locking/locktypes: Further clarifications and wordsmithing m68knommu: Remove mm.h include from uaccess_no.h x86: get rid of user_atomic_cmpxchg_inatomic() generic arch_futex_atomic_op_inuser() doesn't need access_ok() x86: don't reload after cmpxchg in unsafe_atomic_op2() loop x86: convert arch_futex_atomic_op_inuser() to user_access_begin/user_access_end() objtool: whitelist __sanitizer_cov_trace_switch() [parisc, s390, sparc64] no need for access_ok() in futex handling sh: no need of access_ok() in arch_futex_atomic_op_inuser() futex: arch_futex_atomic_op_inuser() calling conventions change completion: Use lockdep_assert_RT_in_threaded_ctx() in complete_all() lockdep: Add posixtimer context tracing bits lockdep: Annotate irq_work lockdep: Add hrtimer context tracing bits lockdep: Introduce wait-type checks completion: Use simple wait queues sched/swait: Prepare usage in completions ...
958 lines
30 KiB
C
958 lines
30 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* Read-Copy Update mechanism for mutual exclusion
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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@linux.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/signal.h>
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#include <linux/sched/debug.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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#include <linux/rcupdate_wait.h>
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#include <linux/sched/isolation.h>
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#include <linux/kprobes.h>
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#include <linux/slab.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_held_common() - might we be in RCU-sched read-side critical section?
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* @ret: Best guess answer if lockdep cannot be relied on
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*
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* Returns true if lockdep must be ignored, in which case *ret contains
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* the best guess described below. Otherwise returns false, in which
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* case *ret tells the caller nothing and the caller should instead
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* consult lockdep.
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*
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* If CONFIG_DEBUG_LOCK_ALLOC is selected, set *ret to 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 view (ie:
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* that we are in the section between rcu_idle_enter() and rcu_idle_exit())
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* then rcu_read_lock_held() sets *ret to false even if the CPU did an
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* rcu_read_lock(). The reason for this is that RCU ignores CPUs that are
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* in such a section, considering these as in extended quiescent state,
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* so such a CPU is effectively never in an RCU read-side critical section
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* regardless of what RCU primitives it invokes. This state of affairs is
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* required --- we need to keep an RCU-free window in idle where the CPU may
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* possibly enter into low power mode. This way we can notice an extended
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* quiescent state to other CPUs that started a grace period. Otherwise
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* we would delay any grace period as long as we run in the idle task.
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*
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* Similarly, we avoid claiming an RCU read lock held if the current
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* CPU is offline.
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*/
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static bool rcu_read_lock_held_common(bool *ret)
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{
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if (!debug_lockdep_rcu_enabled()) {
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*ret = 1;
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return true;
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}
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if (!rcu_is_watching()) {
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*ret = 0;
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return true;
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}
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if (!rcu_lockdep_current_cpu_online()) {
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*ret = 0;
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return true;
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}
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return false;
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}
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int rcu_read_lock_sched_held(void)
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{
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bool ret;
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if (rcu_read_lock_held_common(&ret))
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return ret;
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return lock_is_held(&rcu_sched_lock_map) || !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. (Except during the time period during boot from
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* when the first task is spawned until the rcu_set_runtime_mode()
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* core_initcall() is invoked, at which point everything is expedited.)
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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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rcu_scheduler_active != RCU_SCHEDULER_INIT;
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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 = ATOMIC_INIT(1);
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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 and rcu_scheduler_active into account as well
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* as the rcu_expedite_gp() nesting. So looping on rcu_unexpedite_gp()
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* until rcu_gp_is_expedited() 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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static bool rcu_boot_ended __read_mostly;
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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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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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rcu_boot_ended = 1;
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}
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/*
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* Let rcutorture know when it is OK to turn it up to eleven.
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*/
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bool rcu_inkernel_boot_has_ended(void)
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{
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return rcu_boot_ended;
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}
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EXPORT_SYMBOL_GPL(rcu_inkernel_boot_has_ended);
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#endif /* #ifndef CONFIG_TINY_RCU */
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/*
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* Test each non-SRCU synchronous grace-period wait API. This is
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* useful just after a change in mode for these primitives, and
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* during early boot.
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*/
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void rcu_test_sync_prims(void)
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{
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if (!IS_ENABLED(CONFIG_PROVE_RCU))
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return;
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synchronize_rcu();
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synchronize_rcu_expedited();
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}
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#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
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/*
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* Switch to run-time mode once RCU has fully initialized.
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*/
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static int __init rcu_set_runtime_mode(void)
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{
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rcu_test_sync_prims();
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rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
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kfree_rcu_scheduler_running();
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rcu_test_sync_prims();
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return 0;
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}
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core_initcall(rcu_set_runtime_mode);
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#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
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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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.name = "rcu_read_lock",
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.key = &rcu_lock_key,
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.wait_type_outer = LD_WAIT_FREE,
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.wait_type_inner = LD_WAIT_CONFIG, /* XXX PREEMPT_RCU ? */
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};
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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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.name = "rcu_read_lock_bh",
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.key = &rcu_bh_lock_key,
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.wait_type_outer = LD_WAIT_FREE,
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.wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_LOCK also makes BH preemptible */
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};
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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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.name = "rcu_read_lock_sched",
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.key = &rcu_sched_lock_key,
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.wait_type_outer = LD_WAIT_FREE,
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.wait_type_inner = LD_WAIT_SPIN,
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};
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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 != RCU_SCHEDULER_INACTIVE && 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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NOKPROBE_SYMBOL(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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bool ret;
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if (rcu_read_lock_held_common(&ret))
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return ret;
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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_bh() 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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bool ret;
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if (rcu_read_lock_held_common(&ret))
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return ret;
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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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int rcu_read_lock_any_held(void)
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{
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bool ret;
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if (rcu_read_lock_held_common(&ret))
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return ret;
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if (lock_is_held(&rcu_lock_map) ||
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lock_is_held(&rcu_bh_lock_map) ||
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lock_is_held(&rcu_sched_lock_map))
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return 1;
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return !preemptible();
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}
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EXPORT_SYMBOL_GPL(rcu_read_lock_any_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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int j;
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/* Initialize and register callbacks for each crcu_array element. */
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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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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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for (j = 0; j < i; j++)
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if (crcu_array[j] == crcu_array[i])
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break;
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if (j == i)
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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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continue;
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for (j = 0; j < i; j++)
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if (crcu_array[j] == crcu_array[i])
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break;
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if (j == i)
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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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EXPORT_SYMBOL_GPL(init_rcu_head);
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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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EXPORT_SYMBOL_GPL(destroy_rcu_head);
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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);
|
|
|
|
/**
|
|
* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
|
|
* @head: pointer to rcu_head structure to be initialized
|
|
*
|
|
* This function informs debugobjects that an on-stack rcu_head structure
|
|
* is about to go out of scope. As with init_rcu_head_on_stack(), this
|
|
* function is not required for rcu_head structures that are statically
|
|
* defined or that are dynamically allocated on the heap. Also as with
|
|
* init_rcu_head_on_stack(), this function has no effect for
|
|
* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
|
|
*/
|
|
void destroy_rcu_head_on_stack(struct rcu_head *head)
|
|
{
|
|
debug_object_free(head, &rcuhead_debug_descr);
|
|
}
|
|
EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
|
|
|
|
struct debug_obj_descr rcuhead_debug_descr = {
|
|
.name = "rcu_head",
|
|
.is_static_object = rcuhead_is_static_object,
|
|
};
|
|
EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
|
|
#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
|
|
|
|
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_RCU_TRACE)
|
|
void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
|
|
unsigned long secs,
|
|
unsigned long c_old, unsigned long c)
|
|
{
|
|
trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
|
|
}
|
|
EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
|
|
#else
|
|
#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
|
|
do { } while (0)
|
|
#endif
|
|
|
|
#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST)
|
|
/* Get rcutorture access to sched_setaffinity(). */
|
|
long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
|
|
{
|
|
int ret;
|
|
|
|
ret = sched_setaffinity(pid, in_mask);
|
|
WARN_ONCE(ret, "%s: sched_setaffinity() returned %d\n", __func__, ret);
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcutorture_sched_setaffinity);
|
|
#endif
|
|
|
|
#ifdef CONFIG_RCU_STALL_COMMON
|
|
int rcu_cpu_stall_ftrace_dump __read_mostly;
|
|
module_param(rcu_cpu_stall_ftrace_dump, int, 0644);
|
|
int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings.
|
|
EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
|
|
module_param(rcu_cpu_stall_suppress, int, 0644);
|
|
int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
|
|
module_param(rcu_cpu_stall_timeout, int, 0644);
|
|
#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
|
|
|
|
// Suppress boot-time RCU CPU stall warnings and rcutorture writer stall
|
|
// warnings. Also used by rcutorture even if stall warnings are excluded.
|
|
int rcu_cpu_stall_suppress_at_boot __read_mostly; // !0 = suppress boot stalls.
|
|
EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress_at_boot);
|
|
module_param(rcu_cpu_stall_suppress_at_boot, int, 0444);
|
|
|
|
#ifdef CONFIG_TASKS_RCU
|
|
|
|
/*
|
|
* Simple variant of RCU whose quiescent states are voluntary context
|
|
* switch, cond_resched_rcu_qs(), user-space execution, and idle.
|
|
* As such, grace periods can take one good long time. There are no
|
|
* read-side primitives similar to rcu_read_lock() and rcu_read_unlock()
|
|
* because this implementation is intended to get the system into a safe
|
|
* state for some of the manipulations involved in tracing and the like.
|
|
* Finally, this implementation does not support high call_rcu_tasks()
|
|
* rates from multiple CPUs. If this is required, per-CPU callback lists
|
|
* will be needed.
|
|
*/
|
|
|
|
/* Global list of callbacks and associated lock. */
|
|
static struct rcu_head *rcu_tasks_cbs_head;
|
|
static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
|
|
static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
|
|
static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
|
|
|
|
/* Track exiting tasks in order to allow them to be waited for. */
|
|
DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
|
|
|
|
/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
|
|
#define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
|
|
static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
|
|
module_param(rcu_task_stall_timeout, int, 0644);
|
|
|
|
static struct task_struct *rcu_tasks_kthread_ptr;
|
|
|
|
/**
|
|
* call_rcu_tasks() - Queue an RCU for invocation task-based grace period
|
|
* @rhp: structure to be used for queueing the RCU updates.
|
|
* @func: actual callback function to be invoked after the grace period
|
|
*
|
|
* The callback function will be invoked some time after a full grace
|
|
* period elapses, in other words after all currently executing RCU
|
|
* read-side critical sections have completed. call_rcu_tasks() assumes
|
|
* that the read-side critical sections end at a voluntary context
|
|
* switch (not a preemption!), cond_resched_rcu_qs(), entry into idle,
|
|
* or transition to usermode execution. As such, there are no read-side
|
|
* primitives analogous to rcu_read_lock() and rcu_read_unlock() because
|
|
* this primitive is intended to determine that all tasks have passed
|
|
* through a safe state, not so much for data-strcuture synchronization.
|
|
*
|
|
* See the description of call_rcu() for more detailed information on
|
|
* memory ordering guarantees.
|
|
*/
|
|
void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
|
|
{
|
|
unsigned long flags;
|
|
bool needwake;
|
|
|
|
rhp->next = NULL;
|
|
rhp->func = func;
|
|
raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
|
|
needwake = !rcu_tasks_cbs_head;
|
|
WRITE_ONCE(*rcu_tasks_cbs_tail, rhp);
|
|
rcu_tasks_cbs_tail = &rhp->next;
|
|
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
|
|
/* We can't create the thread unless interrupts are enabled. */
|
|
if (needwake && READ_ONCE(rcu_tasks_kthread_ptr))
|
|
wake_up(&rcu_tasks_cbs_wq);
|
|
}
|
|
EXPORT_SYMBOL_GPL(call_rcu_tasks);
|
|
|
|
/**
|
|
* synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
|
|
*
|
|
* Control will return to the caller some time after a full rcu-tasks
|
|
* grace period has elapsed, in other words after all currently
|
|
* executing rcu-tasks read-side critical sections have elapsed. These
|
|
* read-side critical sections are delimited by calls to schedule(),
|
|
* cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls
|
|
* to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
|
|
*
|
|
* This is a very specialized primitive, intended only for a few uses in
|
|
* tracing and other situations requiring manipulation of function
|
|
* preambles and profiling hooks. The synchronize_rcu_tasks() function
|
|
* is not (yet) intended for heavy use from multiple CPUs.
|
|
*
|
|
* Note that this guarantee implies further memory-ordering guarantees.
|
|
* On systems with more than one CPU, when synchronize_rcu_tasks() returns,
|
|
* each CPU is guaranteed to have executed a full memory barrier since the
|
|
* end of its last RCU-tasks read-side critical section whose beginning
|
|
* preceded the call to synchronize_rcu_tasks(). In addition, each CPU
|
|
* having an RCU-tasks read-side critical section that extends beyond
|
|
* the return from synchronize_rcu_tasks() is guaranteed to have executed
|
|
* a full memory barrier after the beginning of synchronize_rcu_tasks()
|
|
* and before the beginning of that RCU-tasks read-side critical section.
|
|
* Note that these guarantees include CPUs that are offline, idle, or
|
|
* executing in user mode, as well as CPUs that are executing in the kernel.
|
|
*
|
|
* Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
|
|
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
|
|
* to have executed a full memory barrier during the execution of
|
|
* synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
|
|
* (but again only if the system has more than one CPU).
|
|
*/
|
|
void synchronize_rcu_tasks(void)
|
|
{
|
|
/* Complain if the scheduler has not started. */
|
|
RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
|
|
"synchronize_rcu_tasks called too soon");
|
|
|
|
/* Wait for the grace period. */
|
|
wait_rcu_gp(call_rcu_tasks);
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
|
|
|
|
/**
|
|
* rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
|
|
*
|
|
* Although the current implementation is guaranteed to wait, it is not
|
|
* obligated to, for example, if there are no pending callbacks.
|
|
*/
|
|
void rcu_barrier_tasks(void)
|
|
{
|
|
/* There is only one callback queue, so this is easy. ;-) */
|
|
synchronize_rcu_tasks();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
|
|
|
|
/* See if tasks are still holding out, complain if so. */
|
|
static void check_holdout_task(struct task_struct *t,
|
|
bool needreport, bool *firstreport)
|
|
{
|
|
int cpu;
|
|
|
|
if (!READ_ONCE(t->rcu_tasks_holdout) ||
|
|
t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
|
|
!READ_ONCE(t->on_rq) ||
|
|
(IS_ENABLED(CONFIG_NO_HZ_FULL) &&
|
|
!is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
|
|
WRITE_ONCE(t->rcu_tasks_holdout, false);
|
|
list_del_init(&t->rcu_tasks_holdout_list);
|
|
put_task_struct(t);
|
|
return;
|
|
}
|
|
rcu_request_urgent_qs_task(t);
|
|
if (!needreport)
|
|
return;
|
|
if (*firstreport) {
|
|
pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
|
|
*firstreport = false;
|
|
}
|
|
cpu = task_cpu(t);
|
|
pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
|
|
t, ".I"[is_idle_task(t)],
|
|
"N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
|
|
t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
|
|
t->rcu_tasks_idle_cpu, cpu);
|
|
sched_show_task(t);
|
|
}
|
|
|
|
/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
|
|
static int __noreturn rcu_tasks_kthread(void *arg)
|
|
{
|
|
unsigned long flags;
|
|
struct task_struct *g, *t;
|
|
unsigned long lastreport;
|
|
struct rcu_head *list;
|
|
struct rcu_head *next;
|
|
LIST_HEAD(rcu_tasks_holdouts);
|
|
int fract;
|
|
|
|
/* Run on housekeeping CPUs by default. Sysadm can move if desired. */
|
|
housekeeping_affine(current, HK_FLAG_RCU);
|
|
|
|
/*
|
|
* Each pass through the following loop makes one check for
|
|
* newly arrived callbacks, and, if there are some, waits for
|
|
* one RCU-tasks grace period and then invokes the callbacks.
|
|
* This loop is terminated by the system going down. ;-)
|
|
*/
|
|
for (;;) {
|
|
|
|
/* Pick up any new callbacks. */
|
|
raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
|
|
list = rcu_tasks_cbs_head;
|
|
rcu_tasks_cbs_head = NULL;
|
|
rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
|
|
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
|
|
|
|
/* If there were none, wait a bit and start over. */
|
|
if (!list) {
|
|
wait_event_interruptible(rcu_tasks_cbs_wq,
|
|
READ_ONCE(rcu_tasks_cbs_head));
|
|
if (!rcu_tasks_cbs_head) {
|
|
WARN_ON(signal_pending(current));
|
|
schedule_timeout_interruptible(HZ/10);
|
|
}
|
|
continue;
|
|
}
|
|
|
|
/*
|
|
* Wait for all pre-existing t->on_rq and t->nvcsw
|
|
* transitions to complete. Invoking synchronize_rcu()
|
|
* suffices because all these transitions occur with
|
|
* interrupts disabled. Without this synchronize_rcu(),
|
|
* a read-side critical section that started before the
|
|
* grace period might be incorrectly seen as having started
|
|
* after the grace period.
|
|
*
|
|
* This synchronize_rcu() also dispenses with the
|
|
* need for a memory barrier on the first store to
|
|
* ->rcu_tasks_holdout, as it forces the store to happen
|
|
* after the beginning of the grace period.
|
|
*/
|
|
synchronize_rcu();
|
|
|
|
/*
|
|
* There were callbacks, so we need to wait for an
|
|
* RCU-tasks grace period. Start off by scanning
|
|
* the task list for tasks that are not already
|
|
* voluntarily blocked. Mark these tasks and make
|
|
* a list of them in rcu_tasks_holdouts.
|
|
*/
|
|
rcu_read_lock();
|
|
for_each_process_thread(g, t) {
|
|
if (t != current && READ_ONCE(t->on_rq) &&
|
|
!is_idle_task(t)) {
|
|
get_task_struct(t);
|
|
t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
|
|
WRITE_ONCE(t->rcu_tasks_holdout, true);
|
|
list_add(&t->rcu_tasks_holdout_list,
|
|
&rcu_tasks_holdouts);
|
|
}
|
|
}
|
|
rcu_read_unlock();
|
|
|
|
/*
|
|
* Wait for tasks that are in the process of exiting.
|
|
* This does only part of the job, ensuring that all
|
|
* tasks that were previously exiting reach the point
|
|
* where they have disabled preemption, allowing the
|
|
* later synchronize_rcu() to finish the job.
|
|
*/
|
|
synchronize_srcu(&tasks_rcu_exit_srcu);
|
|
|
|
/*
|
|
* Each pass through the following loop scans the list
|
|
* of holdout tasks, removing any that are no longer
|
|
* holdouts. When the list is empty, we are done.
|
|
*/
|
|
lastreport = jiffies;
|
|
|
|
/* Start off with HZ/10 wait and slowly back off to 1 HZ wait*/
|
|
fract = 10;
|
|
|
|
for (;;) {
|
|
bool firstreport;
|
|
bool needreport;
|
|
int rtst;
|
|
struct task_struct *t1;
|
|
|
|
if (list_empty(&rcu_tasks_holdouts))
|
|
break;
|
|
|
|
/* Slowly back off waiting for holdouts */
|
|
schedule_timeout_interruptible(HZ/fract);
|
|
|
|
if (fract > 1)
|
|
fract--;
|
|
|
|
rtst = READ_ONCE(rcu_task_stall_timeout);
|
|
needreport = rtst > 0 &&
|
|
time_after(jiffies, lastreport + rtst);
|
|
if (needreport)
|
|
lastreport = jiffies;
|
|
firstreport = true;
|
|
WARN_ON(signal_pending(current));
|
|
list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
|
|
rcu_tasks_holdout_list) {
|
|
check_holdout_task(t, needreport, &firstreport);
|
|
cond_resched();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Because ->on_rq and ->nvcsw are not guaranteed
|
|
* to have a full memory barriers prior to them in the
|
|
* schedule() path, memory reordering on other CPUs could
|
|
* cause their RCU-tasks read-side critical sections to
|
|
* extend past the end of the grace period. However,
|
|
* because these ->nvcsw updates are carried out with
|
|
* interrupts disabled, we can use synchronize_rcu()
|
|
* to force the needed ordering on all such CPUs.
|
|
*
|
|
* This synchronize_rcu() also confines all
|
|
* ->rcu_tasks_holdout accesses to be within the grace
|
|
* period, avoiding the need for memory barriers for
|
|
* ->rcu_tasks_holdout accesses.
|
|
*
|
|
* In addition, this synchronize_rcu() waits for exiting
|
|
* tasks to complete their final preempt_disable() region
|
|
* of execution, cleaning up after the synchronize_srcu()
|
|
* above.
|
|
*/
|
|
synchronize_rcu();
|
|
|
|
/* Invoke the callbacks. */
|
|
while (list) {
|
|
next = list->next;
|
|
local_bh_disable();
|
|
list->func(list);
|
|
local_bh_enable();
|
|
list = next;
|
|
cond_resched();
|
|
}
|
|
/* Paranoid sleep to keep this from entering a tight loop */
|
|
schedule_timeout_uninterruptible(HZ/10);
|
|
}
|
|
}
|
|
|
|
/* Spawn rcu_tasks_kthread() at core_initcall() time. */
|
|
static int __init rcu_spawn_tasks_kthread(void)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
|
|
if (WARN_ONCE(IS_ERR(t), "%s: Could not start Tasks-RCU grace-period kthread, OOM is now expected behavior\n", __func__))
|
|
return 0;
|
|
smp_mb(); /* Ensure others see full kthread. */
|
|
WRITE_ONCE(rcu_tasks_kthread_ptr, t);
|
|
return 0;
|
|
}
|
|
core_initcall(rcu_spawn_tasks_kthread);
|
|
|
|
/* Do the srcu_read_lock() for the above synchronize_srcu(). */
|
|
void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
|
|
{
|
|
preempt_disable();
|
|
current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
|
|
preempt_enable();
|
|
}
|
|
|
|
/* Do the srcu_read_unlock() for the above synchronize_srcu(). */
|
|
void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
|
|
{
|
|
preempt_disable();
|
|
__srcu_read_unlock(&tasks_rcu_exit_srcu, current->rcu_tasks_idx);
|
|
preempt_enable();
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_TASKS_RCU */
|
|
|
|
#ifndef CONFIG_TINY_RCU
|
|
|
|
/*
|
|
* Print any non-default Tasks RCU settings.
|
|
*/
|
|
static void __init rcu_tasks_bootup_oddness(void)
|
|
{
|
|
#ifdef CONFIG_TASKS_RCU
|
|
if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
|
|
pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
|
|
else
|
|
pr_info("\tTasks RCU enabled.\n");
|
|
#endif /* #ifdef CONFIG_TASKS_RCU */
|
|
}
|
|
|
|
#endif /* #ifndef CONFIG_TINY_RCU */
|
|
|
|
#ifdef CONFIG_PROVE_RCU
|
|
|
|
/*
|
|
* Early boot self test parameters.
|
|
*/
|
|
static bool rcu_self_test;
|
|
module_param(rcu_self_test, bool, 0444);
|
|
|
|
static int rcu_self_test_counter;
|
|
|
|
static void test_callback(struct rcu_head *r)
|
|
{
|
|
rcu_self_test_counter++;
|
|
pr_info("RCU test callback executed %d\n", rcu_self_test_counter);
|
|
}
|
|
|
|
DEFINE_STATIC_SRCU(early_srcu);
|
|
|
|
struct early_boot_kfree_rcu {
|
|
struct rcu_head rh;
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|
};
|
|
|
|
static void early_boot_test_call_rcu(void)
|
|
{
|
|
static struct rcu_head head;
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|
static struct rcu_head shead;
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|
struct early_boot_kfree_rcu *rhp;
|
|
|
|
call_rcu(&head, test_callback);
|
|
if (IS_ENABLED(CONFIG_SRCU))
|
|
call_srcu(&early_srcu, &shead, test_callback);
|
|
rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
|
|
if (!WARN_ON_ONCE(!rhp))
|
|
kfree_rcu(rhp, rh);
|
|
}
|
|
|
|
void rcu_early_boot_tests(void)
|
|
{
|
|
pr_info("Running RCU self tests\n");
|
|
|
|
if (rcu_self_test)
|
|
early_boot_test_call_rcu();
|
|
rcu_test_sync_prims();
|
|
}
|
|
|
|
static int rcu_verify_early_boot_tests(void)
|
|
{
|
|
int ret = 0;
|
|
int early_boot_test_counter = 0;
|
|
|
|
if (rcu_self_test) {
|
|
early_boot_test_counter++;
|
|
rcu_barrier();
|
|
if (IS_ENABLED(CONFIG_SRCU)) {
|
|
early_boot_test_counter++;
|
|
srcu_barrier(&early_srcu);
|
|
}
|
|
}
|
|
if (rcu_self_test_counter != early_boot_test_counter) {
|
|
WARN_ON(1);
|
|
ret = -1;
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
late_initcall(rcu_verify_early_boot_tests);
|
|
#else
|
|
void rcu_early_boot_tests(void) {}
|
|
#endif /* CONFIG_PROVE_RCU */
|
|
|
|
#ifndef CONFIG_TINY_RCU
|
|
|
|
/*
|
|
* Print any significant non-default boot-time settings.
|
|
*/
|
|
void __init rcupdate_announce_bootup_oddness(void)
|
|
{
|
|
if (rcu_normal)
|
|
pr_info("\tNo expedited grace period (rcu_normal).\n");
|
|
else if (rcu_normal_after_boot)
|
|
pr_info("\tNo expedited grace period (rcu_normal_after_boot).\n");
|
|
else if (rcu_expedited)
|
|
pr_info("\tAll grace periods are expedited (rcu_expedited).\n");
|
|
if (rcu_cpu_stall_suppress)
|
|
pr_info("\tRCU CPU stall warnings suppressed (rcu_cpu_stall_suppress).\n");
|
|
if (rcu_cpu_stall_timeout != CONFIG_RCU_CPU_STALL_TIMEOUT)
|
|
pr_info("\tRCU CPU stall warnings timeout set to %d (rcu_cpu_stall_timeout).\n", rcu_cpu_stall_timeout);
|
|
rcu_tasks_bootup_oddness();
|
|
}
|
|
|
|
#endif /* #ifndef CONFIG_TINY_RCU */
|