[PATCH 1/3] mm: memdelay: fix task flags race condition

[Johannes Weiner]

WARNING: CPU: 35 PID: 2263 at ../include/linux/memcontrol.h:466

This is memcg warning that current->memcg_may_oom is set when it
doesn't expect it to.

The warning came in new with the memdelay patches. They add another
task flag in the same int as memcg_may_oom, but modify it from
try_to_wake_up, from a task that isn't current. This isn't safe.

Move the flag to the other int holding task flags, whose modifications
are serialized through the scheduler locks.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 include/linux/sched.h | 2 +-
 kernel/sched/core.c   | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index de15e3c8c43a..d1aa8f4c19ab 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -627,6 +627,7 @@ struct task_struct {
 	unsigned			sched_contributes_to_load:1;
 	unsigned			sched_migrated:1;
 	unsigned			sched_remote_wakeup:1;
+	unsigned			sched_memdelay_requeue:1;
 	/* Force alignment to the next boundary: */
 	unsigned			:0;
 
@@ -651,7 +652,6 @@ struct task_struct {
 	/* disallow userland-initiated cgroup migration */
 	unsigned			no_cgroup_migration:1;
 #endif
-	unsigned			memdelay_migrate_enqueue:1;
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bf105c870da6..b4fa806bf153 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -760,10 +760,10 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 	if (!(flags & ENQUEUE_RESTORE))
 		sched_info_queued(rq, p);
 
-	WARN_ON_ONCE(!(flags & ENQUEUE_WAKEUP) && p->memdelay_migrate_enqueue);
-	if (!(flags & ENQUEUE_WAKEUP) || p->memdelay_migrate_enqueue) {
+	WARN_ON_ONCE(!(flags & ENQUEUE_WAKEUP) && p->sched_memdelay_requeue);
+	if (!(flags & ENQUEUE_WAKEUP) || p->sched_memdelay_requeue) {
 		memdelay_add_runnable(p);
-		p->memdelay_migrate_enqueue = 0;
+		p->sched_memdelay_requeue = 0;
 	} else {
 		memdelay_wakeup(p);
 	}
@@ -2065,8 +2065,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 
 		rq = __task_rq_lock(p, &rf);
 		memdelay_del_sleeping(p);
+		p->sched_memdelay_requeue = 1;
 		__task_rq_unlock(rq, &rf);
-		p->memdelay_migrate_enqueue = 1;
 
 		set_task_cpu(p, cpu);
 	}
-- 
2.14.2


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