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Date: Fri, 30 Mar 2012 08:37:05 +0800
From: Li Zefan <lizefan@huawei.com>
Subject: Re: [PATCH for-3.4-fixes] cgroup: cgroup_attach_task() could return
 -errno after success
In-reply-to: <20120329162620.GD28941@google.com>
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To: Tejun Heo <tj@kernel.org>
Cc: Jiri Kosina <jkosina@suse.cz>, Mandeep Singh Baines <msb@chromium.org>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        Paul Menage <paul@paulmenage.org>, Kay Sievers <kay.sievers@vrfy.org>
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Tejun Heo wrote:

> 61d1d219c4 "cgroup: remove extra calls to find_existing_css_set" made
> cgroup_task_migrate() return void.  An unfortunate side effect was
> that cgroup_attach_task() was depending on that function's return
> value to clear its @retval on the success path.  On cgroup mounts
> without any subsystem with ->can_attach() callback,
> cgroup_attach_task() ended up returning @retval without initializing
> it on success.
> 
> For some reason, gcc failed to warn about it and it didn't cause
> cgroup_attach_task() to return non-zero value in many cases, probably
> due to difference in register allocation.  When the problem
> materializes, systemd fails to populate /systemd cgroup mount and
> fails to boot.
> 
> Fix it by initializing @retval to zero on declaration.
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reported-by: Jiri Kosina <jkosina@suse.cz>
> LKML-Reference: <alpine.LNX.2.00.1203282354440.25526@pobox.suse.cz>


Acked-by: Li Zefan <lizefan@huawei.com>