Re: [PATCH stable v5.8] mm: memcg: fix memcg reclaim soft lockup

[Julius Hemanth Pitti (jpitti)]

On Mon, 2020-09-21 at 18:12 +0200, Greg KH wrote:
> On Thu, Sep 17, 2020 at 06:19:13PM -0700, Julius Hemanth Pitti wrote:
> > From: Xunlei Pang <xlpang@xxxxxxxxxxxxxxxxx>
> > 
> > commit e3336cab2579012b1e72b5265adf98e2d6e244ad upstream.
> > 
> > We've met softlockup with "CONFIG_PREEMPT_NONE=y", when the target
> > memcg
> > doesn't have any reclaimable memory.
> > 
> > It can be easily reproduced as below:
> > 
> >   watchdog: BUG: soft lockup - CPU#0 stuck for
> > 111s![memcg_test:2204]
> >   CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12
> >   Call Trace:
> >     shrink_lruvec+0x49f/0x640
> >     shrink_node+0x2a6/0x6f0
> >     do_try_to_free_pages+0xe9/0x3e0
> >     try_to_free_mem_cgroup_pages+0xef/0x1f0
> >     try_charge+0x2c1/0x750
> >     mem_cgroup_charge+0xd7/0x240
> >     __add_to_page_cache_locked+0x2fd/0x370
> >     add_to_page_cache_lru+0x4a/0xc0
> >     pagecache_get_page+0x10b/0x2f0
> >     filemap_fault+0x661/0xad0
> >     ext4_filemap_fault+0x2c/0x40
> >     __do_fault+0x4d/0xf9
> >     handle_mm_fault+0x1080/0x1790
> > 
> > It only happens on our 1-vcpu instances, because there's no chance
> > for
> > oom reaper to run to reclaim the to-be-killed process.
> > 
> > Add a cond_resched() at the upper shrink_node_memcgs() to solve
> > this
> > issue, this will mean that we will get a scheduling point for each
> > memcg
> > in the reclaimed hierarchy without any dependency on the
> > reclaimable
> > memory in that memcg thus making it more predictable.
> > 
> > Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
> > Signed-off-by: Xunlei Pang <xlpang@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Acked-by: Chris Down <chris@xxxxxxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Link: 
> > http://lkml.kernel.org/r/1598495549-67324-1-git-send-email-xlpang@xxxxxxxxxxxxxxxxx
> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Fixes: b0dedc49a2da ("mm/vmscan.c: iterate only over charged
> > shrinkers during memcg shrink_slab()")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Julius Hemanth Pitti <jpitti@xxxxxxxxx>
> > ---
> >  mm/vmscan.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> 
> The Fixes: tag you show here goes back to 4.19, can you provide a
> 4.19.y
> and 5.4.y version of this as well?
Sure. Will send for both 5.4.y and 4.19.y.

> 
> thanks,
> 
> greg k-h