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![Paul E. McKenney](/assets/img/avatar_default.png)
This patch fixes a long-standing performance bug in classic RCU that results in massive internal-to-RCU lock contention on systems with more than a few hundred CPUs. Although this patch creates a separate flavor of RCU for ease of review and patch maintenance, it is intended to replace classic RCU. This patch still handles stress better than does mainline, so I am still calling it ready for inclusion. This patch is against the -tip tree. Nevertheless, experience on an actual 1000+ CPU machine would still be most welcome. Most of the changes noted below were found while creating an rcutiny (which should permit ejecting the current rcuclassic) and while doing detailed line-by-line documentation. Updates from v9 (http://lkml.org/lkml/2008/12/2/334): o Fixes from remainder of line-by-line code walkthrough, including comment spelling, initialization, undesirable narrowing due to type conversion, removing redundant memory barriers, removing redundant local-variable initialization, and removing redundant local variables. I do not believe that any of these fixes address the CPU-hotplug issues that Andi Kleen was seeing, but please do give it a whirl in case the machine is smarter than I am. A writeup from the walkthrough may be found at the following URL, in case you are suffering from terminal insomnia or masochism: http://www.kernel.org/pub/linux/kernel/people/paulmck/tmp/rcutree-walkthrough.2008.12.16a.pdf o Made rcutree tracing use seq_file, as suggested some time ago by Lai Jiangshan. o Added a .csv variant of the rcudata debugfs trace file, to allow people having thousands of CPUs to drop the data into a spreadsheet. Tested with oocalc and gnumeric. Updated documentation to suit. Updates from v8 (http://lkml.org/lkml/2008/11/15/139): o Fix a theoretical race between grace-period initialization and force_quiescent_state() that could occur if more than three jiffies were required to carry out the grace-period initialization. Which it might, if you had enough CPUs. o Apply Ingo's printk-standardization patch. o Substitute local variables for repeated accesses to global variables. o Fix comment misspellings and redundant (but harmless) increments of ->n_rcu_pending (this latter after having explicitly added it). o Apply checkpatch fixes. Updates from v7 (http://lkml.org/lkml/2008/10/10/291): o Fixed a number of problems noted by Gautham Shenoy, including the cpu-stall-detection bug that he was having difficulty convincing me was real. ;-) o Changed cpu-stall detection to wait for ten seconds rather than three in order to reduce false positive, as suggested by Ingo Molnar. o Produced a design document (http://lwn.net/Articles/305782/). The act of writing this document uncovered a number of both theoretical and "here and now" bugs as noted below. o Fix dynticks_nesting accounting confusion, simplify WARN_ON() condition, fix kerneldoc comments, and add memory barriers in dynticks interface functions. o Add more data to tracing. o Remove unused "rcu_barrier" field from rcu_data structure. o Count calls to rcu_pending() from scheduling-clock interrupt to use as a surrogate timebase should jiffies stop counting. o Fix a theoretical race between force_quiescent_state() and grace-period initialization. Yes, initialization does have to go on for some jiffies for this race to occur, but given enough CPUs... Updates from v6 (http://lkml.org/lkml/2008/9/23/448): o Fix a number of checkpatch.pl complaints. o Apply review comments from Ingo Molnar and Lai Jiangshan on the stall-detection code. o Fix several bugs in !CONFIG_SMP builds. o Fix a misspelled config-parameter name so that RCU now announces at boot time if stall detection is configured. o Run tests on numerous combinations of configurations parameters, which after the fixes above, now build and run correctly. Updates from v5 (http://lkml.org/lkml/2008/9/15/92, bad subject line): o Fix a compiler error in the !CONFIG_FANOUT_EXACT case (blew a changeset some time ago, and finally got around to retesting this option). o Fix some tracing bugs in rcupreempt that caused incorrect totals to be printed. o I now test with a more brutal random-selection online/offline script (attached). Probably more brutal than it needs to be on the people reading it as well, but so it goes. o A number of optimizations and usability improvements: o Make rcu_pending() ignore the grace-period timeout when there is no grace period in progress. o Make force_quiescent_state() avoid going for a global lock in the case where there is no grace period in progress. o Rearrange struct fields to improve struct layout. o Make call_rcu() initiate a grace period if RCU was idle, rather than waiting for the next scheduling clock interrupt. o Invoke rcu_irq_enter() and rcu_irq_exit() only when idle, as suggested by Andi Kleen. I still don't completely trust this change, and might back it out. o Make CONFIG_RCU_TRACE be the single config variable manipulated for all forms of RCU, instead of the prior confusion. o Document tracing files and formats for both rcupreempt and rcutree. Updates from v4 for those missing v5 given its bad subject line: o Separated dynticks interface so that NMIs and irqs call separate functions, greatly simplifying it. In particular, this code no longer requires a proof of correctness. ;-) o Separated dynticks state out into its own per-CPU structure, avoiding the duplicated accounting. o The case where a dynticks-idle CPU runs an irq handler that invokes call_rcu() is now correctly handled, forcing that CPU out of dynticks-idle mode. o Review comments have been applied (thank you all!!!). For but one example, fixed the dynticks-ordering issue that Manfred pointed out, saving me much debugging. ;-) o Adjusted rcuclassic and rcupreempt to handle dynticks changes. Attached is an updated patch to Classic RCU that applies a hierarchy, greatly reducing the contention on the top-level lock for large machines. This passes 10-hour concurrent rcutorture and online-offline testing on 128-CPU ppc64 without dynticks enabled, and exposes some timekeeping bugs in presence of dynticks (exciting working on a system where "sleep 1" hangs until interrupted...), which were fixed in the 2.6.27 kernel. It is getting more reliable than mainline by some measures, so the next version will be against -tip for inclusion. See also Manfred Spraul's recent patches (or his earlier work from 2004 at http://marc.info/?l=linux-kernel&m=108546384711797&w=2). We will converge onto a common patch in the fullness of time, but are currently exploring different regions of the design space. That said, I have already gratefully stolen quite a few of Manfred's ideas. This patch provides CONFIG_RCU_FANOUT, which controls the bushiness of the RCU hierarchy. Defaults to 32 on 32-bit machines and 64 on 64-bit machines. If CONFIG_NR_CPUS is less than CONFIG_RCU_FANOUT, there is no hierarchy. By default, the RCU initialization code will adjust CONFIG_RCU_FANOUT to balance the hierarchy, so strongly NUMA architectures may choose to set CONFIG_RCU_FANOUT_EXACT to disable this balancing, allowing the hierarchy to be exactly aligned to the underlying hardware. Up to two levels of hierarchy are permitted (in addition to the root node), allowing up to 16,384 CPUs on 32-bit systems and up to 262,144 CPUs on 64-bit systems. I just know that I am going to regret saying this, but this seems more than sufficient for the foreseeable future. (Some architectures might wish to set CONFIG_RCU_FANOUT=4, which would limit such architectures to 64 CPUs. If this becomes a real problem, additional levels can be added, but I doubt that it will make a significant difference on real hardware.) In the common case, a given CPU will manipulate its private rcu_data structure and the rcu_node structure that it shares with its immediate neighbors. This can reduce both lock and memory contention by multiple orders of magnitude, which should eliminate the need for the strange manipulations that are reported to be required when running Linux on very large systems. Some shortcomings: o More bugs will probably surface as a result of an ongoing line-by-line code inspection. Patches will be provided as required. o There are probably hangs, rcutorture failures, &c. Seems quite stable on a 128-CPU machine, but that is kind of small compared to 4096 CPUs. However, seems to do better than mainline. Patches will be provided as required. o The memory footprint of this version is several KB larger than rcuclassic. A separate UP-only rcutiny patch will be provided, which will reduce the memory footprint significantly, even compared to the old rcuclassic. One such patch passes light testing, and has a memory footprint smaller even than rcuclassic. Initial reaction from various embedded guys was "it is not worth it", so am putting it aside. Credits: o Manfred Spraul for ideas, review comments, and bugs spotted, as well as some good friendly competition. ;-) o Josh Triplett, Ingo Molnar, Peter Zijlstra, Mathieu Desnoyers, Lai Jiangshan, Andi Kleen, Andy Whitcroft, and Andrew Morton for reviews and comments. o Thomas Gleixner for much-needed help with some timer issues (see patches below). o Jon M. Tollefson, Tim Pepper, Andrew Theurer, Jose R. Santos, Andy Whitcroft, Darrick Wong, Nishanth Aravamudan, Anton Blanchard, Dave Kleikamp, and Nathan Lynch for keeping machines alive despite my heavy abuse^Wtesting. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
1492 lines
41 KiB
C
1492 lines
41 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion, realtime implementation
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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, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright IBM Corporation, 2006
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*
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* Authors: Paul E. McKenney <paulmck@us.ibm.com>
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* With thanks to Esben Nielsen, Bill Huey, and Ingo Molnar
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* for pushing me away from locks and towards counters, and
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* to Suparna Bhattacharya for pushing me completely away
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* from atomic instructions on the read side.
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*
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* - Added handling of Dynamic Ticks
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* Copyright 2007 - Paul E. Mckenney <paulmck@us.ibm.com>
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* - Steven Rostedt <srostedt@redhat.com>
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*
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* Papers: http://www.rdrop.com/users/paulmck/RCU
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*
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* Design Document: http://lwn.net/Articles/253651/
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU/ *.txt
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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/rcupdate.h>
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#include <linux/interrupt.h>
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#include <linux/sched.h>
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#include <asm/atomic.h>
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#include <linux/bitops.h>
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#include <linux/module.h>
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#include <linux/kthread.h>
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#include <linux/completion.h>
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#include <linux/moduleparam.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/random.h>
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#include <linux/delay.h>
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#include <linux/cpumask.h>
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#include <linux/rcupreempt_trace.h>
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#include <asm/byteorder.h>
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/*
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* PREEMPT_RCU data structures.
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*/
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/*
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* GP_STAGES specifies the number of times the state machine has
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* to go through the all the rcu_try_flip_states (see below)
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* in a single Grace Period.
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*
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* GP in GP_STAGES stands for Grace Period ;)
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*/
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#define GP_STAGES 2
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struct rcu_data {
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spinlock_t lock; /* Protect rcu_data fields. */
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long completed; /* Number of last completed batch. */
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int waitlistcount;
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struct rcu_head *nextlist;
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struct rcu_head **nexttail;
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struct rcu_head *waitlist[GP_STAGES];
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struct rcu_head **waittail[GP_STAGES];
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struct rcu_head *donelist; /* from waitlist & waitschedlist */
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struct rcu_head **donetail;
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long rcu_flipctr[2];
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struct rcu_head *nextschedlist;
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struct rcu_head **nextschedtail;
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struct rcu_head *waitschedlist;
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struct rcu_head **waitschedtail;
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int rcu_sched_sleeping;
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#ifdef CONFIG_RCU_TRACE
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struct rcupreempt_trace trace;
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#endif /* #ifdef CONFIG_RCU_TRACE */
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};
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/*
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* States for rcu_try_flip() and friends.
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*/
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enum rcu_try_flip_states {
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/*
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* Stay here if nothing is happening. Flip the counter if somthing
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* starts happening. Denoted by "I"
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*/
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rcu_try_flip_idle_state,
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/*
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* Wait here for all CPUs to notice that the counter has flipped. This
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* prevents the old set of counters from ever being incremented once
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* we leave this state, which in turn is necessary because we cannot
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* test any individual counter for zero -- we can only check the sum.
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* Denoted by "A".
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*/
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rcu_try_flip_waitack_state,
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/*
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* Wait here for the sum of the old per-CPU counters to reach zero.
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* Denoted by "Z".
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*/
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rcu_try_flip_waitzero_state,
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/*
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* Wait here for each of the other CPUs to execute a memory barrier.
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* This is necessary to ensure that these other CPUs really have
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* completed executing their RCU read-side critical sections, despite
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* their CPUs wildly reordering memory. Denoted by "M".
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*/
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rcu_try_flip_waitmb_state,
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};
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/*
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* States for rcu_ctrlblk.rcu_sched_sleep.
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*/
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enum rcu_sched_sleep_states {
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rcu_sched_not_sleeping, /* Not sleeping, callbacks need GP. */
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rcu_sched_sleep_prep, /* Thinking of sleeping, rechecking. */
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rcu_sched_sleeping, /* Sleeping, awaken if GP needed. */
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};
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struct rcu_ctrlblk {
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spinlock_t fliplock; /* Protect state-machine transitions. */
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long completed; /* Number of last completed batch. */
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enum rcu_try_flip_states rcu_try_flip_state; /* The current state of
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the rcu state machine */
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spinlock_t schedlock; /* Protect rcu_sched sleep state. */
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enum rcu_sched_sleep_states sched_sleep; /* rcu_sched state. */
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wait_queue_head_t sched_wq; /* Place for rcu_sched to sleep. */
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};
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static DEFINE_PER_CPU(struct rcu_data, rcu_data);
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static struct rcu_ctrlblk rcu_ctrlblk = {
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.fliplock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.fliplock),
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.completed = 0,
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.rcu_try_flip_state = rcu_try_flip_idle_state,
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.schedlock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.schedlock),
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.sched_sleep = rcu_sched_not_sleeping,
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.sched_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rcu_ctrlblk.sched_wq),
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};
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static struct task_struct *rcu_sched_grace_period_task;
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#ifdef CONFIG_RCU_TRACE
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static char *rcu_try_flip_state_names[] =
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{ "idle", "waitack", "waitzero", "waitmb" };
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#endif /* #ifdef CONFIG_RCU_TRACE */
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static cpumask_t rcu_cpu_online_map __read_mostly = CPU_MASK_NONE;
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/*
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* Enum and per-CPU flag to determine when each CPU has seen
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* the most recent counter flip.
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*/
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enum rcu_flip_flag_values {
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rcu_flip_seen, /* Steady/initial state, last flip seen. */
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/* Only GP detector can update. */
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rcu_flipped /* Flip just completed, need confirmation. */
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/* Only corresponding CPU can update. */
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};
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static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_flip_flag_values, rcu_flip_flag)
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= rcu_flip_seen;
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/*
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* Enum and per-CPU flag to determine when each CPU has executed the
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* needed memory barrier to fence in memory references from its last RCU
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* read-side critical section in the just-completed grace period.
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*/
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enum rcu_mb_flag_values {
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rcu_mb_done, /* Steady/initial state, no mb()s required. */
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/* Only GP detector can update. */
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rcu_mb_needed /* Flip just completed, need an mb(). */
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/* Only corresponding CPU can update. */
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};
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static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_mb_flag_values, rcu_mb_flag)
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= rcu_mb_done;
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/*
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* RCU_DATA_ME: find the current CPU's rcu_data structure.
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* RCU_DATA_CPU: find the specified CPU's rcu_data structure.
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*/
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#define RCU_DATA_ME() (&__get_cpu_var(rcu_data))
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#define RCU_DATA_CPU(cpu) (&per_cpu(rcu_data, cpu))
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/*
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* Helper macro for tracing when the appropriate rcu_data is not
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* cached in a local variable, but where the CPU number is so cached.
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*/
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#define RCU_TRACE_CPU(f, cpu) RCU_TRACE(f, &(RCU_DATA_CPU(cpu)->trace));
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/*
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* Helper macro for tracing when the appropriate rcu_data is not
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* cached in a local variable.
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*/
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#define RCU_TRACE_ME(f) RCU_TRACE(f, &(RCU_DATA_ME()->trace));
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/*
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* Helper macro for tracing when the appropriate rcu_data is pointed
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* to by a local variable.
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*/
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#define RCU_TRACE_RDP(f, rdp) RCU_TRACE(f, &((rdp)->trace));
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#define RCU_SCHED_BATCH_TIME (HZ / 50)
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/*
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* Return the number of RCU batches processed thus far. Useful
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* for debug and statistics.
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*/
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long rcu_batches_completed(void)
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{
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return rcu_ctrlblk.completed;
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed);
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void __rcu_read_lock(void)
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{
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int idx;
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struct task_struct *t = current;
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int nesting;
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nesting = ACCESS_ONCE(t->rcu_read_lock_nesting);
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if (nesting != 0) {
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/* An earlier rcu_read_lock() covers us, just count it. */
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t->rcu_read_lock_nesting = nesting + 1;
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} else {
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unsigned long flags;
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/*
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* We disable interrupts for the following reasons:
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* - If we get scheduling clock interrupt here, and we
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* end up acking the counter flip, it's like a promise
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* that we will never increment the old counter again.
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* Thus we will break that promise if that
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* scheduling clock interrupt happens between the time
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* we pick the .completed field and the time that we
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* increment our counter.
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*
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* - We don't want to be preempted out here.
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*
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* NMIs can still occur, of course, and might themselves
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* contain rcu_read_lock().
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*/
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local_irq_save(flags);
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/*
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* Outermost nesting of rcu_read_lock(), so increment
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* the current counter for the current CPU. Use volatile
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* casts to prevent the compiler from reordering.
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*/
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idx = ACCESS_ONCE(rcu_ctrlblk.completed) & 0x1;
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ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])++;
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/*
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* Now that the per-CPU counter has been incremented, we
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* are protected from races with rcu_read_lock() invoked
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* from NMI handlers on this CPU. We can therefore safely
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* increment the nesting counter, relieving further NMIs
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* of the need to increment the per-CPU counter.
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*/
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ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting + 1;
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/*
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* Now that we have preventing any NMIs from storing
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* to the ->rcu_flipctr_idx, we can safely use it to
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* remember which counter to decrement in the matching
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* rcu_read_unlock().
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*/
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ACCESS_ONCE(t->rcu_flipctr_idx) = idx;
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local_irq_restore(flags);
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}
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}
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EXPORT_SYMBOL_GPL(__rcu_read_lock);
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void __rcu_read_unlock(void)
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{
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int idx;
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struct task_struct *t = current;
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int nesting;
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nesting = ACCESS_ONCE(t->rcu_read_lock_nesting);
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if (nesting > 1) {
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/*
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* We are still protected by the enclosing rcu_read_lock(),
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* so simply decrement the counter.
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*/
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t->rcu_read_lock_nesting = nesting - 1;
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} else {
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unsigned long flags;
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/*
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* Disable local interrupts to prevent the grace-period
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* detection state machine from seeing us half-done.
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* NMIs can still occur, of course, and might themselves
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* contain rcu_read_lock() and rcu_read_unlock().
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*/
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local_irq_save(flags);
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/*
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* Outermost nesting of rcu_read_unlock(), so we must
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* decrement the current counter for the current CPU.
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* This must be done carefully, because NMIs can
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* occur at any point in this code, and any rcu_read_lock()
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* and rcu_read_unlock() pairs in the NMI handlers
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* must interact non-destructively with this code.
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* Lots of volatile casts, and -very- careful ordering.
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*
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* Changes to this code, including this one, must be
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* inspected, validated, and tested extremely carefully!!!
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*/
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/*
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* First, pick up the index.
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*/
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idx = ACCESS_ONCE(t->rcu_flipctr_idx);
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/*
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* Now that we have fetched the counter index, it is
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* safe to decrement the per-task RCU nesting counter.
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* After this, any interrupts or NMIs will increment and
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* decrement the per-CPU counters.
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|
*/
|
|
ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting - 1;
|
|
|
|
/*
|
|
* It is now safe to decrement this task's nesting count.
|
|
* NMIs that occur after this statement will route their
|
|
* rcu_read_lock() calls through this "else" clause, and
|
|
* will thus start incrementing the per-CPU counter on
|
|
* their own. They will also clobber ->rcu_flipctr_idx,
|
|
* but that is OK, since we have already fetched it.
|
|
*/
|
|
|
|
ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])--;
|
|
local_irq_restore(flags);
|
|
}
|
|
}
|
|
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
|
|
|
|
/*
|
|
* If a global counter flip has occurred since the last time that we
|
|
* advanced callbacks, advance them. Hardware interrupts must be
|
|
* disabled when calling this function.
|
|
*/
|
|
static void __rcu_advance_callbacks(struct rcu_data *rdp)
|
|
{
|
|
int cpu;
|
|
int i;
|
|
int wlc = 0;
|
|
|
|
if (rdp->completed != rcu_ctrlblk.completed) {
|
|
if (rdp->waitlist[GP_STAGES - 1] != NULL) {
|
|
*rdp->donetail = rdp->waitlist[GP_STAGES - 1];
|
|
rdp->donetail = rdp->waittail[GP_STAGES - 1];
|
|
RCU_TRACE_RDP(rcupreempt_trace_move2done, rdp);
|
|
}
|
|
for (i = GP_STAGES - 2; i >= 0; i--) {
|
|
if (rdp->waitlist[i] != NULL) {
|
|
rdp->waitlist[i + 1] = rdp->waitlist[i];
|
|
rdp->waittail[i + 1] = rdp->waittail[i];
|
|
wlc++;
|
|
} else {
|
|
rdp->waitlist[i + 1] = NULL;
|
|
rdp->waittail[i + 1] =
|
|
&rdp->waitlist[i + 1];
|
|
}
|
|
}
|
|
if (rdp->nextlist != NULL) {
|
|
rdp->waitlist[0] = rdp->nextlist;
|
|
rdp->waittail[0] = rdp->nexttail;
|
|
wlc++;
|
|
rdp->nextlist = NULL;
|
|
rdp->nexttail = &rdp->nextlist;
|
|
RCU_TRACE_RDP(rcupreempt_trace_move2wait, rdp);
|
|
} else {
|
|
rdp->waitlist[0] = NULL;
|
|
rdp->waittail[0] = &rdp->waitlist[0];
|
|
}
|
|
rdp->waitlistcount = wlc;
|
|
rdp->completed = rcu_ctrlblk.completed;
|
|
}
|
|
|
|
/*
|
|
* Check to see if this CPU needs to report that it has seen
|
|
* the most recent counter flip, thereby declaring that all
|
|
* subsequent rcu_read_lock() invocations will respect this flip.
|
|
*/
|
|
|
|
cpu = raw_smp_processor_id();
|
|
if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) {
|
|
smp_mb(); /* Subsequent counter accesses must see new value */
|
|
per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen;
|
|
smp_mb(); /* Subsequent RCU read-side critical sections */
|
|
/* seen -after- acknowledgement. */
|
|
}
|
|
}
|
|
|
|
DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched) = {
|
|
.dynticks = 1,
|
|
};
|
|
|
|
#ifdef CONFIG_NO_HZ
|
|
static DEFINE_PER_CPU(int, rcu_update_flag);
|
|
|
|
/**
|
|
* rcu_irq_enter - Called from Hard irq handlers and NMI/SMI.
|
|
*
|
|
* If the CPU was idle with dynamic ticks active, this updates the
|
|
* rcu_dyntick_sched.dynticks to let the RCU handling know that the
|
|
* CPU is active.
|
|
*/
|
|
void rcu_irq_enter(void)
|
|
{
|
|
int cpu = smp_processor_id();
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
if (per_cpu(rcu_update_flag, cpu))
|
|
per_cpu(rcu_update_flag, cpu)++;
|
|
|
|
/*
|
|
* Only update if we are coming from a stopped ticks mode
|
|
* (rcu_dyntick_sched.dynticks is even).
|
|
*/
|
|
if (!in_interrupt() &&
|
|
(rdssp->dynticks & 0x1) == 0) {
|
|
/*
|
|
* The following might seem like we could have a race
|
|
* with NMI/SMIs. But this really isn't a problem.
|
|
* Here we do a read/modify/write, and the race happens
|
|
* when an NMI/SMI comes in after the read and before
|
|
* the write. But NMI/SMIs will increment this counter
|
|
* twice before returning, so the zero bit will not
|
|
* be corrupted by the NMI/SMI which is the most important
|
|
* part.
|
|
*
|
|
* The only thing is that we would bring back the counter
|
|
* to a postion that it was in during the NMI/SMI.
|
|
* But the zero bit would be set, so the rest of the
|
|
* counter would again be ignored.
|
|
*
|
|
* On return from the IRQ, the counter may have the zero
|
|
* bit be 0 and the counter the same as the return from
|
|
* the NMI/SMI. If the state machine was so unlucky to
|
|
* see that, it still doesn't matter, since all
|
|
* RCU read-side critical sections on this CPU would
|
|
* have already completed.
|
|
*/
|
|
rdssp->dynticks++;
|
|
/*
|
|
* The following memory barrier ensures that any
|
|
* rcu_read_lock() primitives in the irq handler
|
|
* are seen by other CPUs to follow the above
|
|
* increment to rcu_dyntick_sched.dynticks. This is
|
|
* required in order for other CPUs to correctly
|
|
* determine when it is safe to advance the RCU
|
|
* grace-period state machine.
|
|
*/
|
|
smp_mb(); /* see above block comment. */
|
|
/*
|
|
* Since we can't determine the dynamic tick mode from
|
|
* the rcu_dyntick_sched.dynticks after this routine,
|
|
* we use a second flag to acknowledge that we came
|
|
* from an idle state with ticks stopped.
|
|
*/
|
|
per_cpu(rcu_update_flag, cpu)++;
|
|
/*
|
|
* If we take an NMI/SMI now, they will also increment
|
|
* the rcu_update_flag, and will not update the
|
|
* rcu_dyntick_sched.dynticks on exit. That is for
|
|
* this IRQ to do.
|
|
*/
|
|
}
|
|
}
|
|
|
|
/**
|
|
* rcu_irq_exit - Called from exiting Hard irq context.
|
|
*
|
|
* If the CPU was idle with dynamic ticks active, update the
|
|
* rcu_dyntick_sched.dynticks to put let the RCU handling be
|
|
* aware that the CPU is going back to idle with no ticks.
|
|
*/
|
|
void rcu_irq_exit(void)
|
|
{
|
|
int cpu = smp_processor_id();
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
/*
|
|
* rcu_update_flag is set if we interrupted the CPU
|
|
* when it was idle with ticks stopped.
|
|
* Once this occurs, we keep track of interrupt nesting
|
|
* because a NMI/SMI could also come in, and we still
|
|
* only want the IRQ that started the increment of the
|
|
* rcu_dyntick_sched.dynticks to be the one that modifies
|
|
* it on exit.
|
|
*/
|
|
if (per_cpu(rcu_update_flag, cpu)) {
|
|
if (--per_cpu(rcu_update_flag, cpu))
|
|
return;
|
|
|
|
/* This must match the interrupt nesting */
|
|
WARN_ON(in_interrupt());
|
|
|
|
/*
|
|
* If an NMI/SMI happens now we are still
|
|
* protected by the rcu_dyntick_sched.dynticks being odd.
|
|
*/
|
|
|
|
/*
|
|
* The following memory barrier ensures that any
|
|
* rcu_read_unlock() primitives in the irq handler
|
|
* are seen by other CPUs to preceed the following
|
|
* increment to rcu_dyntick_sched.dynticks. This
|
|
* is required in order for other CPUs to determine
|
|
* when it is safe to advance the RCU grace-period
|
|
* state machine.
|
|
*/
|
|
smp_mb(); /* see above block comment. */
|
|
rdssp->dynticks++;
|
|
WARN_ON(rdssp->dynticks & 0x1);
|
|
}
|
|
}
|
|
|
|
void rcu_nmi_enter(void)
|
|
{
|
|
rcu_irq_enter();
|
|
}
|
|
|
|
void rcu_nmi_exit(void)
|
|
{
|
|
rcu_irq_exit();
|
|
}
|
|
|
|
static void dyntick_save_progress_counter(int cpu)
|
|
{
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
rdssp->dynticks_snap = rdssp->dynticks;
|
|
}
|
|
|
|
static inline int
|
|
rcu_try_flip_waitack_needed(int cpu)
|
|
{
|
|
long curr;
|
|
long snap;
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
curr = rdssp->dynticks;
|
|
snap = rdssp->dynticks_snap;
|
|
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
|
|
|
|
/*
|
|
* If the CPU remained in dynticks mode for the entire time
|
|
* and didn't take any interrupts, NMIs, SMIs, or whatever,
|
|
* then it cannot be in the middle of an rcu_read_lock(), so
|
|
* the next rcu_read_lock() it executes must use the new value
|
|
* of the counter. So we can safely pretend that this CPU
|
|
* already acknowledged the counter.
|
|
*/
|
|
|
|
if ((curr == snap) && ((curr & 0x1) == 0))
|
|
return 0;
|
|
|
|
/*
|
|
* If the CPU passed through or entered a dynticks idle phase with
|
|
* no active irq handlers, then, as above, we can safely pretend
|
|
* that this CPU already acknowledged the counter.
|
|
*/
|
|
|
|
if ((curr - snap) > 2 || (curr & 0x1) == 0)
|
|
return 0;
|
|
|
|
/* We need this CPU to explicitly acknowledge the counter flip. */
|
|
|
|
return 1;
|
|
}
|
|
|
|
static inline int
|
|
rcu_try_flip_waitmb_needed(int cpu)
|
|
{
|
|
long curr;
|
|
long snap;
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
curr = rdssp->dynticks;
|
|
snap = rdssp->dynticks_snap;
|
|
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
|
|
|
|
/*
|
|
* If the CPU remained in dynticks mode for the entire time
|
|
* and didn't take any interrupts, NMIs, SMIs, or whatever,
|
|
* then it cannot have executed an RCU read-side critical section
|
|
* during that time, so there is no need for it to execute a
|
|
* memory barrier.
|
|
*/
|
|
|
|
if ((curr == snap) && ((curr & 0x1) == 0))
|
|
return 0;
|
|
|
|
/*
|
|
* If the CPU either entered or exited an outermost interrupt,
|
|
* SMI, NMI, or whatever handler, then we know that it executed
|
|
* a memory barrier when doing so. So we don't need another one.
|
|
*/
|
|
if (curr != snap)
|
|
return 0;
|
|
|
|
/* We need the CPU to execute a memory barrier. */
|
|
|
|
return 1;
|
|
}
|
|
|
|
static void dyntick_save_progress_counter_sched(int cpu)
|
|
{
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
rdssp->sched_dynticks_snap = rdssp->dynticks;
|
|
}
|
|
|
|
static int rcu_qsctr_inc_needed_dyntick(int cpu)
|
|
{
|
|
long curr;
|
|
long snap;
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
curr = rdssp->dynticks;
|
|
snap = rdssp->sched_dynticks_snap;
|
|
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
|
|
|
|
/*
|
|
* If the CPU remained in dynticks mode for the entire time
|
|
* and didn't take any interrupts, NMIs, SMIs, or whatever,
|
|
* then it cannot be in the middle of an rcu_read_lock(), so
|
|
* the next rcu_read_lock() it executes must use the new value
|
|
* of the counter. Therefore, this CPU has been in a quiescent
|
|
* state the entire time, and we don't need to wait for it.
|
|
*/
|
|
|
|
if ((curr == snap) && ((curr & 0x1) == 0))
|
|
return 0;
|
|
|
|
/*
|
|
* If the CPU passed through or entered a dynticks idle phase with
|
|
* no active irq handlers, then, as above, this CPU has already
|
|
* passed through a quiescent state.
|
|
*/
|
|
|
|
if ((curr - snap) > 2 || (snap & 0x1) == 0)
|
|
return 0;
|
|
|
|
/* We need this CPU to go through a quiescent state. */
|
|
|
|
return 1;
|
|
}
|
|
|
|
#else /* !CONFIG_NO_HZ */
|
|
|
|
# define dyntick_save_progress_counter(cpu) do { } while (0)
|
|
# define rcu_try_flip_waitack_needed(cpu) (1)
|
|
# define rcu_try_flip_waitmb_needed(cpu) (1)
|
|
|
|
# define dyntick_save_progress_counter_sched(cpu) do { } while (0)
|
|
# define rcu_qsctr_inc_needed_dyntick(cpu) (1)
|
|
|
|
#endif /* CONFIG_NO_HZ */
|
|
|
|
static void save_qsctr_sched(int cpu)
|
|
{
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
rdssp->sched_qs_snap = rdssp->sched_qs;
|
|
}
|
|
|
|
static inline int rcu_qsctr_inc_needed(int cpu)
|
|
{
|
|
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
|
|
|
|
/*
|
|
* If there has been a quiescent state, no more need to wait
|
|
* on this CPU.
|
|
*/
|
|
|
|
if (rdssp->sched_qs != rdssp->sched_qs_snap) {
|
|
smp_mb(); /* force ordering with cpu entering schedule(). */
|
|
return 0;
|
|
}
|
|
|
|
/* We need this CPU to go through a quiescent state. */
|
|
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Get here when RCU is idle. Decide whether we need to
|
|
* move out of idle state, and return non-zero if so.
|
|
* "Straightforward" approach for the moment, might later
|
|
* use callback-list lengths, grace-period duration, or
|
|
* some such to determine when to exit idle state.
|
|
* Might also need a pre-idle test that does not acquire
|
|
* the lock, but let's get the simple case working first...
|
|
*/
|
|
|
|
static int
|
|
rcu_try_flip_idle(void)
|
|
{
|
|
int cpu;
|
|
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_i1);
|
|
if (!rcu_pending(smp_processor_id())) {
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_ie1);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Do the flip.
|
|
*/
|
|
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_g1);
|
|
rcu_ctrlblk.completed++; /* stands in for rcu_try_flip_g2 */
|
|
|
|
/*
|
|
* Need a memory barrier so that other CPUs see the new
|
|
* counter value before they see the subsequent change of all
|
|
* the rcu_flip_flag instances to rcu_flipped.
|
|
*/
|
|
|
|
smp_mb(); /* see above block comment. */
|
|
|
|
/* Now ask each CPU for acknowledgement of the flip. */
|
|
|
|
for_each_cpu_mask_nr(cpu, rcu_cpu_online_map) {
|
|
per_cpu(rcu_flip_flag, cpu) = rcu_flipped;
|
|
dyntick_save_progress_counter(cpu);
|
|
}
|
|
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Wait for CPUs to acknowledge the flip.
|
|
*/
|
|
|
|
static int
|
|
rcu_try_flip_waitack(void)
|
|
{
|
|
int cpu;
|
|
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_a1);
|
|
for_each_cpu_mask_nr(cpu, rcu_cpu_online_map)
|
|
if (rcu_try_flip_waitack_needed(cpu) &&
|
|
per_cpu(rcu_flip_flag, cpu) != rcu_flip_seen) {
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_ae1);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Make sure our checks above don't bleed into subsequent
|
|
* waiting for the sum of the counters to reach zero.
|
|
*/
|
|
|
|
smp_mb(); /* see above block comment. */
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_a2);
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Wait for collective ``last'' counter to reach zero,
|
|
* then tell all CPUs to do an end-of-grace-period memory barrier.
|
|
*/
|
|
|
|
static int
|
|
rcu_try_flip_waitzero(void)
|
|
{
|
|
int cpu;
|
|
int lastidx = !(rcu_ctrlblk.completed & 0x1);
|
|
int sum = 0;
|
|
|
|
/* Check to see if the sum of the "last" counters is zero. */
|
|
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_z1);
|
|
for_each_cpu_mask_nr(cpu, rcu_cpu_online_map)
|
|
sum += RCU_DATA_CPU(cpu)->rcu_flipctr[lastidx];
|
|
if (sum != 0) {
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_ze1);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* This ensures that the other CPUs see the call for
|
|
* memory barriers -after- the sum to zero has been
|
|
* detected here
|
|
*/
|
|
smp_mb(); /* ^^^^^^^^^^^^ */
|
|
|
|
/* Call for a memory barrier from each CPU. */
|
|
for_each_cpu_mask_nr(cpu, rcu_cpu_online_map) {
|
|
per_cpu(rcu_mb_flag, cpu) = rcu_mb_needed;
|
|
dyntick_save_progress_counter(cpu);
|
|
}
|
|
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_z2);
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Wait for all CPUs to do their end-of-grace-period memory barrier.
|
|
* Return 0 once all CPUs have done so.
|
|
*/
|
|
|
|
static int
|
|
rcu_try_flip_waitmb(void)
|
|
{
|
|
int cpu;
|
|
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_m1);
|
|
for_each_cpu_mask_nr(cpu, rcu_cpu_online_map)
|
|
if (rcu_try_flip_waitmb_needed(cpu) &&
|
|
per_cpu(rcu_mb_flag, cpu) != rcu_mb_done) {
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_me1);
|
|
return 0;
|
|
}
|
|
|
|
smp_mb(); /* Ensure that the above checks precede any following flip. */
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_m2);
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Attempt a single flip of the counters. Remember, a single flip does
|
|
* -not- constitute a grace period. Instead, the interval between
|
|
* at least GP_STAGES consecutive flips is a grace period.
|
|
*
|
|
* If anyone is nuts enough to run this CONFIG_PREEMPT_RCU implementation
|
|
* on a large SMP, they might want to use a hierarchical organization of
|
|
* the per-CPU-counter pairs.
|
|
*/
|
|
static void rcu_try_flip(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_1);
|
|
if (unlikely(!spin_trylock_irqsave(&rcu_ctrlblk.fliplock, flags))) {
|
|
RCU_TRACE_ME(rcupreempt_trace_try_flip_e1);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Take the next transition(s) through the RCU grace-period
|
|
* flip-counter state machine.
|
|
*/
|
|
|
|
switch (rcu_ctrlblk.rcu_try_flip_state) {
|
|
case rcu_try_flip_idle_state:
|
|
if (rcu_try_flip_idle())
|
|
rcu_ctrlblk.rcu_try_flip_state =
|
|
rcu_try_flip_waitack_state;
|
|
break;
|
|
case rcu_try_flip_waitack_state:
|
|
if (rcu_try_flip_waitack())
|
|
rcu_ctrlblk.rcu_try_flip_state =
|
|
rcu_try_flip_waitzero_state;
|
|
break;
|
|
case rcu_try_flip_waitzero_state:
|
|
if (rcu_try_flip_waitzero())
|
|
rcu_ctrlblk.rcu_try_flip_state =
|
|
rcu_try_flip_waitmb_state;
|
|
break;
|
|
case rcu_try_flip_waitmb_state:
|
|
if (rcu_try_flip_waitmb())
|
|
rcu_ctrlblk.rcu_try_flip_state =
|
|
rcu_try_flip_idle_state;
|
|
}
|
|
spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
|
|
}
|
|
|
|
/*
|
|
* Check to see if this CPU needs to do a memory barrier in order to
|
|
* ensure that any prior RCU read-side critical sections have committed
|
|
* their counter manipulations and critical-section memory references
|
|
* before declaring the grace period to be completed.
|
|
*/
|
|
static void rcu_check_mb(int cpu)
|
|
{
|
|
if (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed) {
|
|
smp_mb(); /* Ensure RCU read-side accesses are visible. */
|
|
per_cpu(rcu_mb_flag, cpu) = rcu_mb_done;
|
|
}
|
|
}
|
|
|
|
void rcu_check_callbacks(int cpu, int user)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
|
|
|
|
/*
|
|
* If this CPU took its interrupt from user mode or from the
|
|
* idle loop, and this is not a nested interrupt, then
|
|
* this CPU has to have exited all prior preept-disable
|
|
* sections of code. So increment the counter to note this.
|
|
*
|
|
* The memory barrier is needed to handle the case where
|
|
* writes from a preempt-disable section of code get reordered
|
|
* into schedule() by this CPU's write buffer. So the memory
|
|
* barrier makes sure that the rcu_qsctr_inc() is seen by other
|
|
* CPUs to happen after any such write.
|
|
*/
|
|
|
|
if (user ||
|
|
(idle_cpu(cpu) && !in_softirq() &&
|
|
hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
|
|
smp_mb(); /* Guard against aggressive schedule(). */
|
|
rcu_qsctr_inc(cpu);
|
|
}
|
|
|
|
rcu_check_mb(cpu);
|
|
if (rcu_ctrlblk.completed == rdp->completed)
|
|
rcu_try_flip();
|
|
spin_lock_irqsave(&rdp->lock, flags);
|
|
RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
|
|
__rcu_advance_callbacks(rdp);
|
|
if (rdp->donelist == NULL) {
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
} else {
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
raise_softirq(RCU_SOFTIRQ);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Needed by dynticks, to make sure all RCU processing has finished
|
|
* when we go idle:
|
|
*/
|
|
void rcu_advance_callbacks(int cpu, int user)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
|
|
|
|
if (rcu_ctrlblk.completed == rdp->completed) {
|
|
rcu_try_flip();
|
|
if (rcu_ctrlblk.completed == rdp->completed)
|
|
return;
|
|
}
|
|
spin_lock_irqsave(&rdp->lock, flags);
|
|
RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
|
|
__rcu_advance_callbacks(rdp);
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
#define rcu_offline_cpu_enqueue(srclist, srctail, dstlist, dsttail) do { \
|
|
*dsttail = srclist; \
|
|
if (srclist != NULL) { \
|
|
dsttail = srctail; \
|
|
srclist = NULL; \
|
|
srctail = &srclist;\
|
|
} \
|
|
} while (0)
|
|
|
|
void rcu_offline_cpu(int cpu)
|
|
{
|
|
int i;
|
|
struct rcu_head *list = NULL;
|
|
unsigned long flags;
|
|
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
|
|
struct rcu_head *schedlist = NULL;
|
|
struct rcu_head **schedtail = &schedlist;
|
|
struct rcu_head **tail = &list;
|
|
|
|
/*
|
|
* Remove all callbacks from the newly dead CPU, retaining order.
|
|
* Otherwise rcu_barrier() will fail
|
|
*/
|
|
|
|
spin_lock_irqsave(&rdp->lock, flags);
|
|
rcu_offline_cpu_enqueue(rdp->donelist, rdp->donetail, list, tail);
|
|
for (i = GP_STAGES - 1; i >= 0; i--)
|
|
rcu_offline_cpu_enqueue(rdp->waitlist[i], rdp->waittail[i],
|
|
list, tail);
|
|
rcu_offline_cpu_enqueue(rdp->nextlist, rdp->nexttail, list, tail);
|
|
rcu_offline_cpu_enqueue(rdp->waitschedlist, rdp->waitschedtail,
|
|
schedlist, schedtail);
|
|
rcu_offline_cpu_enqueue(rdp->nextschedlist, rdp->nextschedtail,
|
|
schedlist, schedtail);
|
|
rdp->rcu_sched_sleeping = 0;
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
rdp->waitlistcount = 0;
|
|
|
|
/* Disengage the newly dead CPU from the grace-period computation. */
|
|
|
|
spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
|
|
rcu_check_mb(cpu);
|
|
if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) {
|
|
smp_mb(); /* Subsequent counter accesses must see new value */
|
|
per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen;
|
|
smp_mb(); /* Subsequent RCU read-side critical sections */
|
|
/* seen -after- acknowledgement. */
|
|
}
|
|
|
|
RCU_DATA_ME()->rcu_flipctr[0] += RCU_DATA_CPU(cpu)->rcu_flipctr[0];
|
|
RCU_DATA_ME()->rcu_flipctr[1] += RCU_DATA_CPU(cpu)->rcu_flipctr[1];
|
|
|
|
RCU_DATA_CPU(cpu)->rcu_flipctr[0] = 0;
|
|
RCU_DATA_CPU(cpu)->rcu_flipctr[1] = 0;
|
|
|
|
cpu_clear(cpu, rcu_cpu_online_map);
|
|
|
|
spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
|
|
|
|
/*
|
|
* Place the removed callbacks on the current CPU's queue.
|
|
* Make them all start a new grace period: simple approach,
|
|
* in theory could starve a given set of callbacks, but
|
|
* you would need to be doing some serious CPU hotplugging
|
|
* to make this happen. If this becomes a problem, adding
|
|
* a synchronize_rcu() to the hotplug path would be a simple
|
|
* fix.
|
|
*/
|
|
|
|
local_irq_save(flags); /* disable preempt till we know what lock. */
|
|
rdp = RCU_DATA_ME();
|
|
spin_lock(&rdp->lock);
|
|
*rdp->nexttail = list;
|
|
if (list)
|
|
rdp->nexttail = tail;
|
|
*rdp->nextschedtail = schedlist;
|
|
if (schedlist)
|
|
rdp->nextschedtail = schedtail;
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
void rcu_offline_cpu(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
void __cpuinit rcu_online_cpu(int cpu)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp;
|
|
|
|
spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
|
|
cpu_set(cpu, rcu_cpu_online_map);
|
|
spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
|
|
|
|
/*
|
|
* The rcu_sched grace-period processing might have bypassed
|
|
* this CPU, given that it was not in the rcu_cpu_online_map
|
|
* when the grace-period scan started. This means that the
|
|
* grace-period task might sleep. So make sure that if this
|
|
* should happen, the first callback posted to this CPU will
|
|
* wake up the grace-period task if need be.
|
|
*/
|
|
|
|
rdp = RCU_DATA_CPU(cpu);
|
|
spin_lock_irqsave(&rdp->lock, flags);
|
|
rdp->rcu_sched_sleeping = 1;
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
}
|
|
|
|
static void rcu_process_callbacks(struct softirq_action *unused)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_head *next, *list;
|
|
struct rcu_data *rdp;
|
|
|
|
local_irq_save(flags);
|
|
rdp = RCU_DATA_ME();
|
|
spin_lock(&rdp->lock);
|
|
list = rdp->donelist;
|
|
if (list == NULL) {
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
return;
|
|
}
|
|
rdp->donelist = NULL;
|
|
rdp->donetail = &rdp->donelist;
|
|
RCU_TRACE_RDP(rcupreempt_trace_done_remove, rdp);
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
while (list) {
|
|
next = list->next;
|
|
list->func(list);
|
|
list = next;
|
|
RCU_TRACE_ME(rcupreempt_trace_invoke);
|
|
}
|
|
}
|
|
|
|
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp;
|
|
|
|
head->func = func;
|
|
head->next = NULL;
|
|
local_irq_save(flags);
|
|
rdp = RCU_DATA_ME();
|
|
spin_lock(&rdp->lock);
|
|
__rcu_advance_callbacks(rdp);
|
|
*rdp->nexttail = head;
|
|
rdp->nexttail = &head->next;
|
|
RCU_TRACE_RDP(rcupreempt_trace_next_add, rdp);
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
}
|
|
EXPORT_SYMBOL_GPL(call_rcu);
|
|
|
|
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp;
|
|
int wake_gp = 0;
|
|
|
|
head->func = func;
|
|
head->next = NULL;
|
|
local_irq_save(flags);
|
|
rdp = RCU_DATA_ME();
|
|
spin_lock(&rdp->lock);
|
|
*rdp->nextschedtail = head;
|
|
rdp->nextschedtail = &head->next;
|
|
if (rdp->rcu_sched_sleeping) {
|
|
|
|
/* Grace-period processing might be sleeping... */
|
|
|
|
rdp->rcu_sched_sleeping = 0;
|
|
wake_gp = 1;
|
|
}
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
if (wake_gp) {
|
|
|
|
/* Wake up grace-period processing, unless someone beat us. */
|
|
|
|
spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
|
|
if (rcu_ctrlblk.sched_sleep != rcu_sched_sleeping)
|
|
wake_gp = 0;
|
|
rcu_ctrlblk.sched_sleep = rcu_sched_not_sleeping;
|
|
spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
|
|
if (wake_gp)
|
|
wake_up_interruptible(&rcu_ctrlblk.sched_wq);
|
|
}
|
|
}
|
|
EXPORT_SYMBOL_GPL(call_rcu_sched);
|
|
|
|
/*
|
|
* Wait until all currently running preempt_disable() code segments
|
|
* (including hardware-irq-disable segments) complete. Note that
|
|
* in -rt this does -not- necessarily result in all currently executing
|
|
* interrupt -handlers- having completed.
|
|
*/
|
|
synchronize_rcu_xxx(__synchronize_sched, call_rcu_sched)
|
|
EXPORT_SYMBOL_GPL(__synchronize_sched);
|
|
|
|
/*
|
|
* kthread function that manages call_rcu_sched grace periods.
|
|
*/
|
|
static int rcu_sched_grace_period(void *arg)
|
|
{
|
|
int couldsleep; /* might sleep after current pass. */
|
|
int couldsleepnext = 0; /* might sleep after next pass. */
|
|
int cpu;
|
|
unsigned long flags;
|
|
struct rcu_data *rdp;
|
|
int ret;
|
|
|
|
/*
|
|
* Each pass through the following loop handles one
|
|
* rcu_sched grace period cycle.
|
|
*/
|
|
do {
|
|
/* Save each CPU's current state. */
|
|
|
|
for_each_online_cpu(cpu) {
|
|
dyntick_save_progress_counter_sched(cpu);
|
|
save_qsctr_sched(cpu);
|
|
}
|
|
|
|
/*
|
|
* Sleep for about an RCU grace-period's worth to
|
|
* allow better batching and to consume less CPU.
|
|
*/
|
|
schedule_timeout_interruptible(RCU_SCHED_BATCH_TIME);
|
|
|
|
/*
|
|
* If there was nothing to do last time, prepare to
|
|
* sleep at the end of the current grace period cycle.
|
|
*/
|
|
couldsleep = couldsleepnext;
|
|
couldsleepnext = 1;
|
|
if (couldsleep) {
|
|
spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
|
|
rcu_ctrlblk.sched_sleep = rcu_sched_sleep_prep;
|
|
spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
|
|
}
|
|
|
|
/*
|
|
* Wait on each CPU in turn to have either visited
|
|
* a quiescent state or been in dynticks-idle mode.
|
|
*/
|
|
for_each_online_cpu(cpu) {
|
|
while (rcu_qsctr_inc_needed(cpu) &&
|
|
rcu_qsctr_inc_needed_dyntick(cpu)) {
|
|
/* resched_cpu(cpu); @@@ */
|
|
schedule_timeout_interruptible(1);
|
|
}
|
|
}
|
|
|
|
/* Advance callbacks for each CPU. */
|
|
|
|
for_each_online_cpu(cpu) {
|
|
|
|
rdp = RCU_DATA_CPU(cpu);
|
|
spin_lock_irqsave(&rdp->lock, flags);
|
|
|
|
/*
|
|
* We are running on this CPU irq-disabled, so no
|
|
* CPU can go offline until we re-enable irqs.
|
|
* The current CPU might have already gone
|
|
* offline (between the for_each_offline_cpu and
|
|
* the spin_lock_irqsave), but in that case all its
|
|
* callback lists will be empty, so no harm done.
|
|
*
|
|
* Advance the callbacks! We share normal RCU's
|
|
* donelist, since callbacks are invoked the
|
|
* same way in either case.
|
|
*/
|
|
if (rdp->waitschedlist != NULL) {
|
|
*rdp->donetail = rdp->waitschedlist;
|
|
rdp->donetail = rdp->waitschedtail;
|
|
|
|
/*
|
|
* Next rcu_check_callbacks() will
|
|
* do the required raise_softirq().
|
|
*/
|
|
}
|
|
if (rdp->nextschedlist != NULL) {
|
|
rdp->waitschedlist = rdp->nextschedlist;
|
|
rdp->waitschedtail = rdp->nextschedtail;
|
|
couldsleep = 0;
|
|
couldsleepnext = 0;
|
|
} else {
|
|
rdp->waitschedlist = NULL;
|
|
rdp->waitschedtail = &rdp->waitschedlist;
|
|
}
|
|
rdp->nextschedlist = NULL;
|
|
rdp->nextschedtail = &rdp->nextschedlist;
|
|
|
|
/* Mark sleep intention. */
|
|
|
|
rdp->rcu_sched_sleeping = couldsleep;
|
|
|
|
spin_unlock_irqrestore(&rdp->lock, flags);
|
|
}
|
|
|
|
/* If we saw callbacks on the last scan, go deal with them. */
|
|
|
|
if (!couldsleep)
|
|
continue;
|
|
|
|
/* Attempt to block... */
|
|
|
|
spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
|
|
if (rcu_ctrlblk.sched_sleep != rcu_sched_sleep_prep) {
|
|
|
|
/*
|
|
* Someone posted a callback after we scanned.
|
|
* Go take care of it.
|
|
*/
|
|
spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
|
|
couldsleepnext = 0;
|
|
continue;
|
|
}
|
|
|
|
/* Block until the next person posts a callback. */
|
|
|
|
rcu_ctrlblk.sched_sleep = rcu_sched_sleeping;
|
|
spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
|
|
ret = 0;
|
|
__wait_event_interruptible(rcu_ctrlblk.sched_wq,
|
|
rcu_ctrlblk.sched_sleep != rcu_sched_sleeping,
|
|
ret);
|
|
|
|
/*
|
|
* Signals would prevent us from sleeping, and we cannot
|
|
* do much with them in any case. So flush them.
|
|
*/
|
|
if (ret)
|
|
flush_signals(current);
|
|
couldsleepnext = 0;
|
|
|
|
} while (!kthread_should_stop());
|
|
|
|
return (0);
|
|
}
|
|
|
|
/*
|
|
* Check to see if any future RCU-related work will need to be done
|
|
* by the current CPU, even if none need be done immediately, returning
|
|
* 1 if so. Assumes that notifiers would take care of handling any
|
|
* outstanding requests from the RCU core.
|
|
*
|
|
* This function is part of the RCU implementation; it is -not-
|
|
* an exported member of the RCU API.
|
|
*/
|
|
int rcu_needs_cpu(int cpu)
|
|
{
|
|
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
|
|
|
|
return (rdp->donelist != NULL ||
|
|
!!rdp->waitlistcount ||
|
|
rdp->nextlist != NULL ||
|
|
rdp->nextschedlist != NULL ||
|
|
rdp->waitschedlist != NULL);
|
|
}
|
|
|
|
int rcu_pending(int cpu)
|
|
{
|
|
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
|
|
|
|
/* The CPU has at least one callback queued somewhere. */
|
|
|
|
if (rdp->donelist != NULL ||
|
|
!!rdp->waitlistcount ||
|
|
rdp->nextlist != NULL ||
|
|
rdp->nextschedlist != NULL ||
|
|
rdp->waitschedlist != NULL)
|
|
return 1;
|
|
|
|
/* The RCU core needs an acknowledgement from this CPU. */
|
|
|
|
if ((per_cpu(rcu_flip_flag, cpu) == rcu_flipped) ||
|
|
(per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed))
|
|
return 1;
|
|
|
|
/* This CPU has fallen behind the global grace-period number. */
|
|
|
|
if (rdp->completed != rcu_ctrlblk.completed)
|
|
return 1;
|
|
|
|
/* Nothing needed from this CPU. */
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
|
|
unsigned long action, void *hcpu)
|
|
{
|
|
long cpu = (long)hcpu;
|
|
|
|
switch (action) {
|
|
case CPU_UP_PREPARE:
|
|
case CPU_UP_PREPARE_FROZEN:
|
|
rcu_online_cpu(cpu);
|
|
break;
|
|
case CPU_UP_CANCELED:
|
|
case CPU_UP_CANCELED_FROZEN:
|
|
case CPU_DEAD:
|
|
case CPU_DEAD_FROZEN:
|
|
rcu_offline_cpu(cpu);
|
|
break;
|
|
default:
|
|
break;
|
|
}
|
|
return NOTIFY_OK;
|
|
}
|
|
|
|
static struct notifier_block __cpuinitdata rcu_nb = {
|
|
.notifier_call = rcu_cpu_notify,
|
|
};
|
|
|
|
void __init __rcu_init(void)
|
|
{
|
|
int cpu;
|
|
int i;
|
|
struct rcu_data *rdp;
|
|
|
|
printk(KERN_NOTICE "Preemptible RCU implementation.\n");
|
|
for_each_possible_cpu(cpu) {
|
|
rdp = RCU_DATA_CPU(cpu);
|
|
spin_lock_init(&rdp->lock);
|
|
rdp->completed = 0;
|
|
rdp->waitlistcount = 0;
|
|
rdp->nextlist = NULL;
|
|
rdp->nexttail = &rdp->nextlist;
|
|
for (i = 0; i < GP_STAGES; i++) {
|
|
rdp->waitlist[i] = NULL;
|
|
rdp->waittail[i] = &rdp->waitlist[i];
|
|
}
|
|
rdp->donelist = NULL;
|
|
rdp->donetail = &rdp->donelist;
|
|
rdp->rcu_flipctr[0] = 0;
|
|
rdp->rcu_flipctr[1] = 0;
|
|
rdp->nextschedlist = NULL;
|
|
rdp->nextschedtail = &rdp->nextschedlist;
|
|
rdp->waitschedlist = NULL;
|
|
rdp->waitschedtail = &rdp->waitschedlist;
|
|
rdp->rcu_sched_sleeping = 0;
|
|
}
|
|
register_cpu_notifier(&rcu_nb);
|
|
|
|
/*
|
|
* We don't need protection against CPU-Hotplug here
|
|
* since
|
|
* a) If a CPU comes online while we are iterating over the
|
|
* cpu_online_map below, we would only end up making a
|
|
* duplicate call to rcu_online_cpu() which sets the corresponding
|
|
* CPU's mask in the rcu_cpu_online_map.
|
|
*
|
|
* b) A CPU cannot go offline at this point in time since the user
|
|
* does not have access to the sysfs interface, nor do we
|
|
* suspend the system.
|
|
*/
|
|
for_each_online_cpu(cpu)
|
|
rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu);
|
|
|
|
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
|
|
}
|
|
|
|
/*
|
|
* Late-boot-time RCU initialization that must wait until after scheduler
|
|
* has been initialized.
|
|
*/
|
|
void __init rcu_init_sched(void)
|
|
{
|
|
rcu_sched_grace_period_task = kthread_run(rcu_sched_grace_period,
|
|
NULL,
|
|
"rcu_sched_grace_period");
|
|
WARN_ON(IS_ERR(rcu_sched_grace_period_task));
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_TRACE
|
|
long *rcupreempt_flipctr(int cpu)
|
|
{
|
|
return &RCU_DATA_CPU(cpu)->rcu_flipctr[0];
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcupreempt_flipctr);
|
|
|
|
int rcupreempt_flip_flag(int cpu)
|
|
{
|
|
return per_cpu(rcu_flip_flag, cpu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcupreempt_flip_flag);
|
|
|
|
int rcupreempt_mb_flag(int cpu)
|
|
{
|
|
return per_cpu(rcu_mb_flag, cpu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcupreempt_mb_flag);
|
|
|
|
char *rcupreempt_try_flip_state_name(void)
|
|
{
|
|
return rcu_try_flip_state_names[rcu_ctrlblk.rcu_try_flip_state];
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcupreempt_try_flip_state_name);
|
|
|
|
struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu)
|
|
{
|
|
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
|
|
|
|
return &rdp->trace;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcupreempt_trace_cpu);
|
|
|
|
#endif /* #ifdef RCU_TRACE */
|