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Commit 7f4d454d authored by Daisuke Nishimura's avatar Daisuke Nishimura Committed by Linus Torvalds
Browse files

memcg: avoid deadlock caused by race between oom and cpuset_attach 



mpol_rebind_mm(), which can be called from cpuset_attach(), does
down_write(mm->mmap_sem).  This means down_write(mm->mmap_sem) can be
called under cgroup_mutex.

OTOH, page fault path does down_read(mm->mmap_sem) and calls
mem_cgroup_try_charge_xxx(), which may eventually calls
mem_cgroup_out_of_memory().  And mem_cgroup_out_of_memory() calls
cgroup_lock().  This means cgroup_lock() can be called under
down_read(mm->mmap_sem).

If those two paths race, deadlock can happen.

This patch avoid this deadlock by:
  - remove cgroup_lock() from mem_cgroup_out_of_memory().
  - define new mutex (memcg_tasklist) and serialize mem_cgroup_move_task()
    (->attach handler of memory cgroup) and mem_cgroup_out_of_memory.

Signed-off-by: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarBalbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a5e924f5

mm/memcontrol.c

+5 −0
Original line number Original line Diff line number Diff line
@@ -51,6 +51,7 @@ static int really_do_swap_account __initdata = 1; /* for remember boot option*/ 
#define do_swap_account		(0)

#define do_swap_account		(0)

#endif

#endif





static DEFINE_MUTEX(memcg_tasklist);	/* can be hold under cgroup_mutex */





/*

/*

 * Statistics for memory cgroup.

 * Statistics for memory cgroup.
@@ -827,7 +828,9 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, 




		if (!nr_retries--) {

		if (!nr_retries--) {

			if (oom) {

			if (oom) {

				mutex_lock(&memcg_tasklist);

				mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);

				mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);

				mutex_unlock(&memcg_tasklist);

				mem_over_limit->last_oom_jiffies = jiffies;

				mem_over_limit->last_oom_jiffies = jiffies;

			}

			}

			goto nomem;

			goto nomem;
@@ -2211,10 +2214,12 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss, 
				struct cgroup *old_cont,

				struct cgroup *old_cont,

				struct task_struct *p)

				struct task_struct *p)

{

{

	mutex_lock(&memcg_tasklist);

	/*

	/*

	 * FIXME: It's better to move charges of this process from old

	 * FIXME: It's better to move charges of this process from old

	 * memcg to new memcg. But it's just on TODO-List now.

	 * memcg to new memcg. But it's just on TODO-List now.

	 */

	 */

	mutex_unlock(&memcg_tasklist);

}

}





struct cgroup_subsys mem_cgroup_subsys = {

struct cgroup_subsys mem_cgroup_subsys = {

mm/oom_kill.c

+0 −2
Original line number Original line Diff line number Diff line
@@ -429,7 +429,6 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask) 
	unsigned long points = 0;

	unsigned long points = 0;

	struct task_struct *p;

	struct task_struct *p;





	cgroup_lock();

	read_lock(&tasklist_lock);

	read_lock(&tasklist_lock);

retry:

retry:

	p = select_bad_process(&points, mem);

	p = select_bad_process(&points, mem);
@@ -444,7 +443,6 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask) 
		goto retry;

		goto retry;

out:

out:

	read_unlock(&tasklist_lock);

	read_unlock(&tasklist_lock);

	cgroup_unlock();

}

}

#endif

#endif