diff options
authorRoman Gushchin <>2019-11-15 17:34:43 -0800
committerLinus Torvalds <>2019-11-15 18:34:00 -0800
commit00d484f354d85845991b40141d40ba9e5eb60faf (patch)
parent8e20ba2e53fc6198cbfbcc700e9f884157052a8d (diff)
mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm()
We've encountered a rcu stall in get_mem_cgroup_from_mm(): rcu: INFO: rcu_sched self-detected stall on CPU rcu: 33-....: (21000 ticks this GP) idle=6c6/1/0x4000000000000002 softirq=35441/35441 fqs=5017 (t=21031 jiffies g=324821 q=95837) NMI backtrace for cpu 33 <...> RIP: 0010:get_mem_cgroup_from_mm+0x2f/0x90 <...> __memcg_kmem_charge+0x55/0x140 __alloc_pages_nodemask+0x267/0x320 pipe_write+0x1ad/0x400 new_sync_write+0x127/0x1c0 __kernel_write+0x4f/0xf0 dump_emit+0x91/0xc0 writenote+0xa0/0xc0 elf_core_dump+0x11af/0x1430 do_coredump+0xc65/0xee0 get_signal+0x132/0x7c0 do_signal+0x36/0x640 exit_to_usermode_loop+0x61/0xd0 do_syscall_64+0xd4/0x100 entry_SYSCALL_64_after_hwframe+0x44/0xa9 The problem is caused by an exiting task which is associated with an offline memcg. We're iterating over and over in the do {} while (!css_tryget_online()) loop, but obviously the memcg won't become online and the exiting task won't be migrated to a live memcg. Let's fix it by switching from css_tryget_online() to css_tryget(). As css_tryget_online() cannot guarantee that the memcg won't go offline, the check is usually useless, except some rare cases when for example it determines if something should be presented to a user. A similar problem is described by commit 18fa84a2db0e ("cgroup: Use css_tryget() instead of css_tryget_online() in task_get_css()"). Johannes: : The bug aside, it doesn't matter whether the cgroup is online for the : callers. It used to matter when offlining needed to evacuate all charges : from the memcg, and so needed to prevent new ones from showing up, but we : don't care now. Link: Signed-off-by: Roman Gushchin <> Acked-by: Johannes Weiner <> Acked-by: Tejun Heo <> Reviewed-by: Shakeel Butt <> Cc: Michal Hocko <> Cc: Michal Koutn <> Cc: <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 37592dd7ae32..46ad252e6d6a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -960,7 +960,7 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
if (unlikely(!memcg))
memcg = root_mem_cgroup;
- } while (!css_tryget_online(&memcg->css));
+ } while (!css_tryget(&memcg->css));
return memcg;