On Tue 17-03-20 17:55:04, David Rientjes wrote:
> When a process is oom killed as a result of memcg limits and the victim
> is waiting to exit, nothing ends up actually yielding the processor back
> to the victim on UP systems with preemption disabled. Instead, the
> charging process simply loops in memcg reclaim and eventually soft
> lockups.
It seems that my request to describe the setup got ignored. Sigh.
> Memory cgroup out of memory: Killed process 808 (repro) total-vm:41944kB,
> anon-rss:35344kB, file-rss:504kB, shmem-rss:0kB, UID:0 pgtables:108kB
> oom_score_adj:0
> watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [repro:806]
> CPU: 0 PID: 806 Comm: repro Not tainted 5.6.0-rc5+ #136
> RIP: 0010:shrink_lruvec+0x4e9/0xa40
> ...
> Call Trace:
> shrink_node+0x40d/0x7d0
> do_try_to_free_pages+0x13f/0x470
> try_to_free_mem_cgroup_pages+0x16d/0x230
> try_charge+0x247/0xac0
> mem_cgroup_try_charge+0x10a/0x220
> mem_cgroup_try_charge_delay+0x1e/0x40
> handle_mm_fault+0xdf2/0x15f0
> do_user_addr_fault+0x21f/0x420
> page_fault+0x2f/0x40
>
> Make sure that once the oom killer has been called that we forcibly yield
> if current is not the chosen victim regardless of priority to allow for
> memory freeing. The same situation can theoretically occur in the page
> allocator, so do this after dropping oom_lock there as well.
I would have prefered the cond_resched solution proposed previously but
I can live with this as well. I would just ask to add more information
to the changelog. E.g.
"
We used to have a short sleep after the oom handling but 9bfe5ded054b
("mm, oom: remove sleep from under oom_lock") has removed it because
sleep inside the oom_lock is dangerous. This patch restores the sleep
outside of the lock.
"
> Suggested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Tested-by: Robert Kolchmeyer <rkolchmeyer@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/memcontrol.c | 2 ++
> mm/page_alloc.c | 2 ++
> 2 files changed, 4 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1576,6 +1576,8 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> */
> ret = should_force_charge() || out_of_memory(&oc);
> mutex_unlock(&oom_lock);
> + if (!fatal_signal_pending(current))
> + schedule_timeout_killable(1);
Check for fatal_signal_pending is redundant.
--
Michal Hocko
SUSE Labs
