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

[Linux-MTD Mailing List]

Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=0b26351b910fb8fe6a056f8a1bbccabe50c0e19f
Commit:     0b26351b910fb8fe6a056f8a1bbccabe50c0e19f
Parent:     f4ef6a438cee86ca0c6d1b889aa53bec9c1f9de6
Author:     Peter Zijlstra <peterz at infradead.org>
AuthorDate: Fri Apr 20 11:50:05 2018 +0200
Committer:  Ingo Molnar <mingo at kernel.org>
CommitDate: Thu May 3 07:38:03 2018 +0200

    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: Peter Zijlstra (Intel) <peterz at infradead.org>
    Reported-by: Matt Fleming <matt at codeblueprint.co.uk>
    Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
    Acked-by: Matt Fleming <matt at codeblueprint.co.uk>
    Cc: Linus Torvalds <torvalds at linux-foundation.org>
    Cc: Michal Hocko <mhocko at suse.com>
    Cc: Mike Galbraith <umgwanakikbuti at gmail.com>
    Cc: Peter Zijlstra <peterz at infradead.org>
    Cc: Thomas Gleixner <tglx at linutronix.de>
    Link: http://lkml.kernel.org/r/20180420095005.GH4064@hirez.programming.kicks-ass.net
    Signed-off-by: Ingo Molnar <mingo at kernel.org>
---
 kernel/stop_machine.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index b7591261652d..64c0291b579c 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -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 @@ retry:
 			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 @@ unlock:
 			cpu_relax();
 		goto retry;
 	}
+
+	wake_up_q(&wakeq);
+
 	return err;
 }
 /**