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Date: Wed, 23 Sep 2015 18:50:22 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [patch] mm, oom: remove task_lock protecting comm printing
Message-ID: <20150923095022.GB640@swordfish>
References: <alpine.DEB.2.10.1509221629440.7794@chino.kir.corp.google.com>
 <20150923080632.GD12318@esperanza>
 <20150923091354.GA640@swordfish>
 <20150923093021.GE12318@esperanza>
 <20150923094358.GB8644@dhcp22.suse.cz>
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To: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, David Rientjes <rientjes@google.com>, Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Linus Torvalds <torvalds@linux-foundation.org>, Kyle Walker <kwalker@redhat.com>, Christoph Lameter <cl@linux.com>, Johannes Weiner <hannes@cmpxchg.org>, linux-mm <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Stanislav Kozina <skozina@redhat.com>, Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>

On (09/23/15 11:43), Michal Hocko wrote:
[..]
> > > the previous name was already null terminated,
> > 
> > Yeah, but if the old name is shorter than the new one, set_task_comm()
> > overwrites the terminating null of the old name before writing the new
> > terminating null, so there is a short time window during which tsk->comm
> > might be not null-terminated, no?
> 
> Not really:
>         case PR_SET_NAME:
>                 comm[sizeof(me->comm) - 1] = 0;
>                 if (strncpy_from_user(comm, (char __user *)arg2,
>                                       sizeof(me->comm) - 1) < 0)
>                         return -EFAULT;
> 
> So it first writes the terminating 0 and only then starts copying.

right.

hm, shouldn't set_task_comm()->__set_task_comm() do the same?

	-ss

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