Messages in this thread Patch in this message |  | | Date | Mon, 26 Sep 2011 16:45:59 -0700 | | From | Andrew Morton <> | | Subject | Re: [PATCH] memcg: Fix race condition in memcg_check_events() with this_cpu usage |
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On Mon, 26 Sep 2011 09:43:22 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Fri, 23 Sep 2011 20:54:42 -0400 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > From: Steven Rostedt <srostedt@redhat.com> > > > > The code in memcg_check_events() calls this_cpu_read() on > > different variables without disabling preemption, and can cause > > the calculations to be done from two different CPU variables. > > > > Disable preemption throughout the check to keep apples and oranges > > from becoming a mixed drink. > > > > [ Added this_cpu to __this_cpu conversion by Johannes ] > > > > 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: Andrew Morton <akpm@linux-foundation.org> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Cc: Christoph Lameter <cl@linux.com> > > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> > > Signed-off-by: Steven Rostedt <rostedt@goodmis.org> > > Link: http://lkml.kernel.org/r/20110919212641.015320989@goodmis.org > > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > Andrew, could you pick this up ?
The patch needed rework due to other changes we have pending in there.
From: Steven Rostedt <srostedt@redhat.com> Subject: 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.
[ Added this_cpu to __this_cpu conversion by Johannes ]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Steven 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: Andrew Morton <akpm@linux-foundation.org> ---
mm/memcontrol.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff -puN mm/memcontrol.c~memcg-fix-race-condition-in-memcg_check_events-with-this_cpu-usage mm/memcontrol.c --- a/mm/memcontrol.c~memcg-fix-race-condition-in-memcg_check_events-with-this_cpu-usage +++ a/mm/memcontrol.c @@ -687,8 +687,8 @@ static bool __memcg_event_check(struct m { 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); } @@ -697,7 +697,7 @@ static void __mem_cgroup_target_update(s { 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: @@ -713,7 +713,7 @@ static void __mem_cgroup_target_update(s return; } - this_cpu_write(memcg->stat->targets[target], next); + __this_cpu_write(memcg->stat->targets[target], next); } /* @@ -722,6 +722,7 @@ static void __mem_cgroup_target_update(s */ 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); @@ -741,6 +742,7 @@ static void memcg_check_events(struct me } #endif } + preempt_enable(); } static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont) _
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