linux-kernel - Re: [RFC] ps command race fix

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Message-Id: <20060724190030.34884a67.akpm@osdl.org>
Date:	Mon, 24 Jul 2006 19:00:30 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Paul Jackson <pj@....com>
Cc:	kamezawa.hiroyu@...fujitsu.com, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com
Subject: Re: [RFC] ps command race fix

On Mon, 24 Jul 2006 18:48:47 -0700
Paul Jackson <pj@....com> wrote:

> Another possibility (perhaps a really stupid idea ;) would be to
> snapshot the list of pids on the open, and let the readdir() just
> access that fixed array.

The patch under discussion does precisely this.  (Awkwardly.  Using
kmalloc-pre-object might be better).

> The kernel/cpuset.c cpuset_tasks_open() routine that displays the
> pids of tasks in a cpuset (the per-cpuset 'tasks' file) does this.

Your faith in large kmalloc()s is touching ;) I guess the number of pids
will be smaller for cpusets.

> Then the seek and read and such semantics are nice and stable and
> simple.
> 
> Throw out the snapshot on the last close.

The patch under discussion didn't do this, although it could.  But it still
permits rather a lot of kernel memory to be pinned.

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