linux-kernel - Re: [PATCH 2/2] core: allow setrlimit to non-current tasks

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Message-ID: <4A9EBCF8.1020609@gmail.com>
Date:	Wed, 02 Sep 2009 20:44:08 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	akpm@...ux-foundation.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] core: allow setrlimit to non-current tasks

On 09/02/2009 03:50 PM, Oleg Nesterov wrote:
> But there is another minor problem. If we use read_lock(ttasklist), then
> the write to /proc/application_pid/limits can race with application doing
> sys_setrlimits().
> 
> Nothing bad can happen, but this means that "echo ... > /proc/limits" can
> be lost. Not good, if admin wants to lower ->rlim_max we should try to ensure
> this always works.

Actually, process cpu timer may be set to a wrong value. When
* somebody unrelated holds sighand->siglock
* process one stores rlim_new to rlim and gets stuck on spin_lock(siglock)
* process two does the same
* somebody releases sighand->siglock
* process one continues...

I can't think of anything else than doing all the checks and updates
under alloc_lock, introducing coarse grained static mutex in setrlimit
to protect it, or some other(I-don't-know-of)/new lock. Any ideas?

Thanks.
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