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From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Sasha Levin <sasha.levin@oracle.com>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org,
	cgroups@vger.kernel.org, linux-mm@kvack.org,
	vdavydov@parallels.com, kernel-team@fb.com
Subject: Re: [PATCH 1/2] memcg: flatten task_struct->memcg_oom
Date: Mon, 21 Sep 2015 16:01:41 -0400	[thread overview]
Message-ID: <20150921200141.GH13263@mtj.duckdns.org> (raw)
In-Reply-To: <55FEC685.5010404@oracle.com>

(cc'ing scheduler folks)

On Sun, Sep 20, 2015 at 10:45:25AM -0400, Sasha Levin wrote:
> On 09/13/2015 02:59 PM, Tejun Heo wrote:
> > task_struct->memcg_oom is a sub-struct containing fields which are
> > used for async memcg oom handling.  Most task_struct fields aren't
> > packaged this way and it can lead to unnecessary alignment paddings.
> > This patch flattens it.
> > 
> > * task.memcg_oom.memcg          -> task.memcg_in_oom
> > * task.memcg_oom.gfp_mask	-> task.memcg_oom_gfp_mask
> > * task.memcg_oom.order          -> task.memcg_oom_order
> > * task.memcg_oom.may_oom        -> task.memcg_may_oom
...
> I've started seeing these warnings:
> 
> [1598889.250160] WARNING: CPU: 3 PID: 11648 at include/linux/memcontrol.h:414 handle_mm_fault+0x1020/0x3fa0()
...
> [1598892.247256] dump_stack (lib/dump_stack.c:52)
> [1598892.249105] warn_slowpath_common (kernel/panic.c:448)
> [1598892.253202] warn_slowpath_null (kernel/panic.c:482)
> [1598892.255148] handle_mm_fault (include/linux/memcontrol.h:414 mm/memory.c:3430)
> [1598892.268151] __do_page_fault (arch/x86/mm/fault.c:1239)
> [1598892.269022] trace_do_page_fault (arch/x86/mm/fault.c:1331 include/linux/jump_label.h:133 include/linux/context_tracking_state.h:30 include/linux/context_tracking.h:46 arch/x86/mm/fault.c:1332)
> [1598892.269894] do_async_page_fault (arch/x86/kernel/kvm.c:280)
> [1598892.270792] async_page_fault (arch/x86/entry/entry_64.S:989)
> 
> Not sure if it's because of this patch or not, but I haven't seen them before.

So, the only way the patch could have caused the above is if someone
who isn't the task itself is writing to the bitfields while the task
is running.  Looking through the fields, ->sched_reset_on_fork seems a
bit suspicious.  __sched_setscheduler() looks like it can modify the
bit while the target task is running.  Peter, am I misreading the
code?

Thanks.

-- 
tejun

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WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Sasha Levin <sasha.levin-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
Cc: akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org,
	hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org,
	mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	vdavydov-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org,
	kernel-team-b10kYP2dOMg@public.gmane.org
Subject: Re: [PATCH 1/2] memcg: flatten task_struct->memcg_oom
Date: Mon, 21 Sep 2015 16:01:41 -0400	[thread overview]
Message-ID: <20150921200141.GH13263@mtj.duckdns.org> (raw)
In-Reply-To: <55FEC685.5010404-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>

(cc'ing scheduler folks)

On Sun, Sep 20, 2015 at 10:45:25AM -0400, Sasha Levin wrote:
> On 09/13/2015 02:59 PM, Tejun Heo wrote:
> > task_struct->memcg_oom is a sub-struct containing fields which are
> > used for async memcg oom handling.  Most task_struct fields aren't
> > packaged this way and it can lead to unnecessary alignment paddings.
> > This patch flattens it.
> > 
> > * task.memcg_oom.memcg          -> task.memcg_in_oom
> > * task.memcg_oom.gfp_mask	-> task.memcg_oom_gfp_mask
> > * task.memcg_oom.order          -> task.memcg_oom_order
> > * task.memcg_oom.may_oom        -> task.memcg_may_oom
...
> I've started seeing these warnings:
> 
> [1598889.250160] WARNING: CPU: 3 PID: 11648 at include/linux/memcontrol.h:414 handle_mm_fault+0x1020/0x3fa0()
...
> [1598892.247256] dump_stack (lib/dump_stack.c:52)
> [1598892.249105] warn_slowpath_common (kernel/panic.c:448)
> [1598892.253202] warn_slowpath_null (kernel/panic.c:482)
> [1598892.255148] handle_mm_fault (include/linux/memcontrol.h:414 mm/memory.c:3430)
> [1598892.268151] __do_page_fault (arch/x86/mm/fault.c:1239)
> [1598892.269022] trace_do_page_fault (arch/x86/mm/fault.c:1331 include/linux/jump_label.h:133 include/linux/context_tracking_state.h:30 include/linux/context_tracking.h:46 arch/x86/mm/fault.c:1332)
> [1598892.269894] do_async_page_fault (arch/x86/kernel/kvm.c:280)
> [1598892.270792] async_page_fault (arch/x86/entry/entry_64.S:989)
> 
> Not sure if it's because of this patch or not, but I haven't seen them before.

So, the only way the patch could have caused the above is if someone
who isn't the task itself is writing to the bitfields while the task
is running.  Looking through the fields, ->sched_reset_on_fork seems a
bit suspicious.  __sched_setscheduler() looks like it can modify the
bit while the target task is running.  Peter, am I misreading the
code?

Thanks.

-- 
tejun

  reply	other threads:[~2015-09-21 20:01 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-13 18:59 [PATCH 1/2] memcg: flatten task_struct->memcg_oom Tejun Heo
2015-09-13 18:59 ` Tejun Heo
2015-09-13 19:00 ` [PATCH v3 2/2] memcg: punt high overage reclaim to return-to-userland path Tejun Heo
2015-09-15  7:47   ` Johannes Weiner
2015-09-15  7:47     ` Johannes Weiner
2015-09-15 15:53     ` Tejun Heo
2015-09-15 16:12       ` Johannes Weiner
2015-09-15 16:22         ` Tejun Heo
2015-09-15 16:22           ` Tejun Heo
2015-09-15 16:33           ` Johannes Weiner
2015-09-15 16:33             ` Johannes Weiner
2015-09-15  7:37 ` [PATCH 1/2] memcg: flatten task_struct->memcg_oom Johannes Weiner
2015-09-15  7:37   ` Johannes Weiner
2015-09-20 14:45 ` Sasha Levin
2015-09-20 14:45   ` Sasha Levin
2015-09-21 20:01   ` Tejun Heo [this message]
2015-09-21 20:01     ` Tejun Heo
2015-09-30 18:54     ` Tejun Heo
2015-09-30 18:54       ` Tejun Heo
2015-11-25 14:43     ` Peter Zijlstra
2015-11-25 14:43       ` Peter Zijlstra
2015-11-25 15:02       ` Peter Zijlstra
2015-11-25 15:02         ` Peter Zijlstra
2015-11-25 15:31         ` Andrey Ryabinin
2015-11-25 17:34           ` Dmitry Vyukov
2015-11-25 17:34             ` Dmitry Vyukov
2015-11-25 17:44           ` Peter Zijlstra
2015-12-11 16:25             ` Tejun Heo
2015-12-11 16:25               ` Tejun Heo
2015-12-15 19:22               ` Peter Zijlstra
2015-12-30  9:23                 ` [PATCH v4.4-rc7] sched: isolate task_struct bitfields according to synchronization domains Tejun Heo
2015-12-30 20:10                   ` Linus Torvalds
2015-12-30 20:10                     ` Linus Torvalds
2015-12-30 20:17                     ` Linus Torvalds
2015-12-30 20:41                     ` Tejun Heo
2015-12-30 20:41                       ` Tejun Heo
2015-12-30 20:43                       ` Linus Torvalds
2016-01-01  2:56                     ` [PATCH v4.4-rc7] sched: move sched lock synchronized bitfields in task_struct into ->atomic_flags Tejun Heo
2016-01-01  2:56                       ` Tejun Heo
2016-01-06 13:44                       ` Tejun Heo
2016-01-06 13:44                         ` Tejun Heo
2016-01-06 18:48         ` [tip:sched/core] sched/core: Fix unserialized r-m-w scribbling stuff tip-bot for Peter Zijlstra
2016-01-06 20:17           ` Tejun Heo
  -- strict thread matches above, loose matches on Subject: below --
2015-08-28 22:01 [PATCH 1/2] memcg: flatten task_struct->memcg_oom Tejun Heo
2015-08-28 22:01 ` Tejun Heo
2015-09-01 15:25 ` Michal Hocko
2015-09-01 15:25   ` Michal Hocko
2015-09-02 11:45 ` Vladimir Davydov
2015-09-02 11:45   ` Vladimir Davydov

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