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Commit 4799401f authored by Steven Rostedt's avatar Steven Rostedt Committed by Linus Torvalds
Browse files

memcg: Fix race condition in memcg_check_events() with this_cpu usage 



Various code in memcontrol.c () calls this_cpu_read() on the calculations
to be done from two different percpu variables, or does an open-coded
read-modify-write on a single percpu variable.

Disable preemption throughout these operations so that the writes go to
the correct palces.

[hannes@cmpxchg.org: added this_cpu to __this_cpu conversion]
Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Cc: Greg Thelen <gthelen@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a61ed3ce

mm/memcontrol.c

+6 −4
Original line number Diff line number Diff line
@@ -686,8 +686,8 @@ static bool __memcg_event_check(struct mem_cgroup *memcg, int target) 
{

	unsigned long val, next;



	val = this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);

	next = this_cpu_read(memcg->stat->targets[target]);

	val = __this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);

	next = __this_cpu_read(memcg->stat->targets[target]);

	/* from time_after() in jiffies.h */

	return ((long)next - (long)val < 0);

}
@@ -696,7 +696,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target) 
{

	unsigned long val, next;



	val = this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);

	val = __this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);



	switch (target) {

	case MEM_CGROUP_TARGET_THRESH:
@@ -712,7 +712,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target) 
		return;

	}



	this_cpu_write(memcg->stat->targets[target], next);

	__this_cpu_write(memcg->stat->targets[target], next);

}



/*
@@ -721,6 +721,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target) 
 */

static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)

{

	preempt_disable();

	/* threshold event is triggered in finer grain than soft limit */

	if (unlikely(__memcg_event_check(memcg, MEM_CGROUP_TARGET_THRESH))) {

		mem_cgroup_threshold(memcg);
@@ -740,6 +741,7 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page) 
		}

#endif

	}

	preempt_enable();

}



static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)