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: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 435f08d..8610370 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -51,6 +51,7 @@
#define do_swap_account (0)
#endif
+static DEFINE_MUTEX(memcg_tasklist); /* can be hold under cgroup_mutex */
/*
* Statistics for memory cgroup.
@@ -827,7 +828,9 @@
if (!nr_retries--) {
if (oom) {
+ mutex_lock(&memcg_tasklist);
mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);
+ mutex_unlock(&memcg_tasklist);
mem_over_limit->last_oom_jiffies = jiffies;
}
goto nomem;
@@ -2211,10 +2214,12 @@
struct cgroup *old_cont,
struct task_struct *p)
{
+ mutex_lock(&memcg_tasklist);
/*
* FIXME: It's better to move charges of this process from old
* memcg to new memcg. But it's just on TODO-List now.
*/
+ mutex_unlock(&memcg_tasklist);
}
struct cgroup_subsys mem_cgroup_subsys = {
