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From: Roman Gushchin <guro@fb.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Kernel Team <Kernel-team@fb.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm()
Date: Thu, 7 Nov 2019 16:42:41 +0000	[thread overview]
Message-ID: <20191107164236.GB2919@castle.dhcp.thefacebook.com> (raw)
In-Reply-To: <20191107122125.GS8314@dhcp22.suse.cz>

On Thu, Nov 07, 2019 at 01:21:25PM +0100, Michal Hocko wrote:
> On Wed 06-11-19 14:51:30, Roman Gushchin wrote:
> > 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
> >  ? unix_stream_sendmsg+0x37d/0x3b0
> >  get_signal+0x132/0x7c0
> >  do_signal+0x36/0x640
> >  ? recalc_sigpending+0x17/0x50
> >  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.
> 
> Hmm, how can we have a task in an offline memcg? I thought that any
> existing task will prevent cgroup removal from proceeding. Is this some
> sort of race where the task managed to disassociate from the cgroup
> while there is still a binding to a memcg existing? What am I missing?

It's an exiting task with the PF_EXITING flag set and it's in their late stages
of life.


  parent reply	other threads:[~2019-11-07 16:42 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-06 22:51 [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() Roman Gushchin
2019-11-06 22:51 ` [PATCH 2/2] mm: hugetlb: switch to css_tryget() in hugetlb_cgroup_charge_cgroup() Roman Gushchin
2019-11-07  0:26   ` Johannes Weiner
2019-11-07  2:31   ` Shakeel Butt
2019-11-07 15:44   ` Tejun Heo
2019-11-07  0:22 ` [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() Johannes Weiner
2019-11-07  1:25   ` Shakeel Butt
2019-11-07  1:43     ` Johannes Weiner
2019-11-07  1:43     ` Roman Gushchin
2019-11-07  2:21       ` Shakeel Butt
2019-11-07  2:28         ` Shakeel Butt
2019-11-07 12:21 ` Michal Hocko
2019-11-07 15:43   ` Tejun Heo
2019-11-07 16:42   ` Roman Gushchin [this message]
2019-11-07 17:02     ` Michal Hocko
2019-11-07 22:41       ` Roman Gushchin
2019-11-08  8:53         ` Michal Hocko
2019-11-07 15:43 ` Tejun Heo
2019-11-13 16:29 ` Michal Koutný
2019-11-13 17:08   ` Roman Gushchin
2019-11-14 19:16     ` Michal Hocko
2019-11-14 19:20       ` Tejun Heo
2019-11-14 19:33         ` Michal Hocko
2019-11-14 19:37           ` Tejun Heo
2019-11-15 17:40             ` Michal Hocko
2019-11-15 17:45               ` Tejun Heo
2019-11-15 17:47               ` Michal Hocko
2019-11-15 17:48                 ` Tejun Heo
2019-11-15 18:03                   ` Michal Hocko
2019-11-15 18:07                 ` Roman Gushchin
2019-11-18  9:43                   ` Michal Hocko
2019-11-15 18:13       ` Roman Gushchin
2019-11-21 15:28     ` Michal Koutný
2019-11-22  8:20       ` Michal Hocko

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