linux-kernel - Re: [RFC][PATCH] ps command race fix take2 [4/4] proc_pid

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Date:	22 Aug 2006 13:11:30 +0200
From:	Andi Kleen <ak@...e.de>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...l.org>, ebiederm@...ssion.com, pj@....com,
	saito.tadashi@...t.fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] ps command race fix take2 [4/4] proc_pid_readdir

KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:

> proc_pid_readdir() by list_token.
> 
> Remember 'where we are reading' by inserting a token in the list.
> It seems a bit complicated because of RCU but what we do is very simple.
> 

What happens when you have multiple readers at the same time? Can't
the tokens then be mixed up?

>+		/* this small kmalloc() can fail in rare case, but readdir()
>+		 * is not allowed to return ENOMEM. retrying is reasonable. */

Who disallows this? Such retry loops are normally discouraged 
because they can lead to deadlocks in OOM situations.
I think it would be better to just return ENOMEM.

-Andi
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