linux-kernel - Re: [PATCH v3] kthread: Make kthread

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Message-ID: <alpine.DEB.2.02.1309251351001.27471@chino.kir.corp.google.com>
Date:	Wed, 25 Sep 2013 14:05:02 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
cc:	akpm@...ux-foundation.org, oleg@...hat.com, security@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] kthread: Make kthread_create() killable.

On Wed, 25 Sep 2013, Tetsuo Handa wrote:

> Any users of wait_for_completion() might be chosen by the OOM killer while
> waiting for completion() call by some process which does memory
> allocation.  kthread_create() is one of such users.
> 

Any user process callers of wait_for_completion() you mean.

> When such users are chosen by the OOM killer when they are waiting for
> completion() in TASK_UNINTERRUPTIBLE, the system will be kept stressed
> due to memory starvation because the OOM killer cannot kill such users.
> 

Also results in a livelock if you're running in a memcg and have hit its 
limit.

> Fix this problem for kthreadd by making kthread_create() killable.
> 

There appear to be other potential callers of wait_for_completion() in the 
tree as well that could be holding lots of memory besides 
kthread_create().

Perhaps that's beyond the scope of this particular patch, though.

wait_for_completion() is scary if that completion requires memory that 
cannot be allocated because the caller is killed but uninterruptible.

> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Acked-by: David Rientjes <rientjes@...gle.com>
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