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Message-ID: <tip-b17718d02f54b90978d0e0146368b512b11c3e84@git.kernel.org>
Date: Fri, 19 Jun 2015 11:00:39 -0700
From: tip-bot for Peter Zijlstra <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: akpm@...ux-foundation.org, bp@...en8.de,
torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
peterz@...radead.org, mingo@...nel.org, jolsa@...hat.com,
riel@...hat.com, hpa@...or.com, oleg@...hat.com, tglx@...utronix.de
Subject: [tip:sched/core] sched/stop_machine:
Fix deadlock between multiple stop_two_cpus()
Commit-ID: b17718d02f54b90978d0e0146368b512b11c3e84
Gitweb: http://git.kernel.org/tip/b17718d02f54b90978d0e0146368b512b11c3e84
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Fri, 5 Jun 2015 17:30:23 +0200
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 19 Jun 2015 10:03:12 +0200
sched/stop_machine: Fix deadlock between multiple stop_two_cpus()
Jiri reported a machine stuck in multi_cpu_stop() with
migrate_swap_stop() as function and with the following src,dst cpu
pairs: {11, 4} {13, 11} { 4, 13}
4 11 13
cpuM: queue(4 ,13)
*Ma
cpuN: queue(13,11)
*N Na
*M Mb
cpuO: queue(11, 4)
*O Oa
*Nb
*Ob
Where *X denotes the cpu running the queueing of cpu-X and X[ab] denotes
the first/second queued work.
You'll observe the top of the workqueue for each cpu: 4,11,13 to be work
from cpus: M, O, N resp. IOW. deadlock.
Do away with the queueing trickery and introduce lg_double_lock() to
lock both CPUs and fully serialize the stop_two_cpus() callers instead
of the partial (and buggy) serialization we have now.
Reported-by: Jiri Olsa <jolsa@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20150605153023.GH19282@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
include/linux/lglock.h | 5 +++++
kernel/locking/lglock.c | 22 ++++++++++++++++++++++
kernel/stop_machine.c | 42 +++++-------------------------------------
3 files changed, 32 insertions(+), 37 deletions(-)
diff --git a/include/linux/lglock.h b/include/linux/lglock.h
index 0081f00..c92ebd1 100644
--- a/include/linux/lglock.h
+++ b/include/linux/lglock.h
@@ -52,10 +52,15 @@ struct lglock {
static struct lglock name = { .lock = &name ## _lock }
void lg_lock_init(struct lglock *lg, char *name);
+
void lg_local_lock(struct lglock *lg);
void lg_local_unlock(struct lglock *lg);
void lg_local_lock_cpu(struct lglock *lg, int cpu);
void lg_local_unlock_cpu(struct lglock *lg, int cpu);
+
+void lg_double_lock(struct lglock *lg, int cpu1, int cpu2);
+void lg_double_unlock(struct lglock *lg, int cpu1, int cpu2);
+
void lg_global_lock(struct lglock *lg);
void lg_global_unlock(struct lglock *lg);
diff --git a/kernel/locking/lglock.c b/kernel/locking/lglock.c
index 86ae2ae..951cfcd 100644
--- a/kernel/locking/lglock.c
+++ b/kernel/locking/lglock.c
@@ -60,6 +60,28 @@ void lg_local_unlock_cpu(struct lglock *lg, int cpu)
}
EXPORT_SYMBOL(lg_local_unlock_cpu);
+void lg_double_lock(struct lglock *lg, int cpu1, int cpu2)
+{
+ BUG_ON(cpu1 == cpu2);
+
+ /* lock in cpu order, just like lg_global_lock */
+ if (cpu2 < cpu1)
+ swap(cpu1, cpu2);
+
+ preempt_disable();
+ lock_acquire_shared(&lg->lock_dep_map, 0, 0, NULL, _RET_IP_);
+ arch_spin_lock(per_cpu_ptr(lg->lock, cpu1));
+ arch_spin_lock(per_cpu_ptr(lg->lock, cpu2));
+}
+
+void lg_double_unlock(struct lglock *lg, int cpu1, int cpu2)
+{
+ lock_release(&lg->lock_dep_map, 1, _RET_IP_);
+ arch_spin_unlock(per_cpu_ptr(lg->lock, cpu1));
+ arch_spin_unlock(per_cpu_ptr(lg->lock, cpu2));
+ preempt_enable();
+}
+
void lg_global_lock(struct lglock *lg)
{
int i;
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 695f0c6..fd643d8 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -211,25 +211,6 @@ static int multi_cpu_stop(void *data)
return err;
}
-struct irq_cpu_stop_queue_work_info {
- int cpu1;
- int cpu2;
- struct cpu_stop_work *work1;
- struct cpu_stop_work *work2;
-};
-
-/*
- * This function is always run with irqs and preemption disabled.
- * This guarantees that both work1 and work2 get queued, before
- * our local migrate thread gets the chance to preempt us.
- */
-static void irq_cpu_stop_queue_work(void *arg)
-{
- struct irq_cpu_stop_queue_work_info *info = arg;
- cpu_stop_queue_work(info->cpu1, info->work1);
- cpu_stop_queue_work(info->cpu2, info->work2);
-}
-
/**
* stop_two_cpus - stops two cpus
* @cpu1: the cpu to stop
@@ -245,7 +226,6 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
{
struct cpu_stop_done done;
struct cpu_stop_work work1, work2;
- struct irq_cpu_stop_queue_work_info call_args;
struct multi_stop_data msdata;
preempt_disable();
@@ -262,13 +242,6 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
.done = &done
};
- call_args = (struct irq_cpu_stop_queue_work_info){
- .cpu1 = cpu1,
- .cpu2 = cpu2,
- .work1 = &work1,
- .work2 = &work2,
- };
-
cpu_stop_init_done(&done, 2);
set_state(&msdata, MULTI_STOP_PREPARE);
@@ -285,16 +258,11 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
return -ENOENT;
}
- lg_local_lock(&stop_cpus_lock);
- /*
- * Queuing needs to be done by the lowest numbered CPU, to ensure
- * that works are always queued in the same order on every CPU.
- * This prevents deadlocks.
- */
- smp_call_function_single(min(cpu1, cpu2),
- &irq_cpu_stop_queue_work,
- &call_args, 1);
- lg_local_unlock(&stop_cpus_lock);
+ lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
+ cpu_stop_queue_work(cpu1, &work1);
+ cpu_stop_queue_work(cpu2, &work2);
+ lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
+
preempt_enable();
wait_for_completion(&done.completion);
--
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