Commit 0b26351b authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar

stop_machine, sched: Fix migrate_swap() vs. active_balance() deadlock

Matt reported the following deadlock:

CPU0					CPU1

schedule(.prev=migrate/0)		<fault>
  pick_next_task()			  ...
    idle_balance()			    migrate_swap()
      active_balance()			      stop_two_cpus()
						spin_lock(stopper0->lock)
						spin_lock(stopper1->lock)
						ttwu(migrate/0)
						  smp_cond_load_acquire() -- waits for schedule()
        stop_one_cpu(1)
	  spin_lock(stopper1->lock) -- waits for stopper lock

Fix this deadlock by taking the wakeups out from under stopper->lock.
This allows the active_balance() to queue the stop work and finish the
context switch, which in turn allows the wakeup from migrate_swap() to
observe the context and complete the wakeup.
Signed-off-by: 's avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: 's avatarMatt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: 's avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: 's avatarMatt Fleming <matt@codeblueprint.co.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180420095005.GH4064@hirez.programming.kicks-ass.netSigned-off-by: 's avatarIngo Molnar <mingo@kernel.org>
parent f4ef6a43
......@@ -21,6 +21,7 @@
#include <linux/smpboot.h>
#include <linux/atomic.h>
#include <linux/nmi.h>
#include <linux/sched/wake_q.h>
/*
* Structure to determine completion condition and record errors. May
......@@ -65,27 +66,31 @@ static void cpu_stop_signal_done(struct cpu_stop_done *done)
}
static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
struct cpu_stop_work *work)
struct cpu_stop_work *work,
struct wake_q_head *wakeq)
{
list_add_tail(&work->list, &stopper->works);
wake_up_process(stopper->thread);
wake_q_add(wakeq, stopper->thread);
}
/* queue @work to @stopper. if offline, @work is completed immediately */
static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
DEFINE_WAKE_Q(wakeq);
unsigned long flags;
bool enabled;
spin_lock_irqsave(&stopper->lock, flags);
enabled = stopper->enabled;
if (enabled)
__cpu_stop_queue_work(stopper, work);
__cpu_stop_queue_work(stopper, work, &wakeq);
else if (work->done)
cpu_stop_signal_done(work->done);
spin_unlock_irqrestore(&stopper->lock, flags);
wake_up_q(&wakeq);
return enabled;
}
......@@ -229,6 +234,7 @@ static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
{
struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
DEFINE_WAKE_Q(wakeq);
int err;
retry:
spin_lock_irq(&stopper1->lock);
......@@ -252,8 +258,8 @@ static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
goto unlock;
err = 0;
__cpu_stop_queue_work(stopper1, work1);
__cpu_stop_queue_work(stopper2, work2);
__cpu_stop_queue_work(stopper1, work1, &wakeq);
__cpu_stop_queue_work(stopper2, work2, &wakeq);
unlock:
spin_unlock(&stopper2->lock);
spin_unlock_irq(&stopper1->lock);
......@@ -263,6 +269,9 @@ static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
cpu_relax();
goto retry;
}
wake_up_q(&wakeq);
return err;
}
/**
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment