linux-kernel - Re: [PATCH] fs/file.c: __fget() and dup2() atomicity rules

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Message-ID: <20150629174616.GZ17109@ZenIV.linux.org.uk>
Date:	Mon, 29 Jun 2015 18:46:16 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs/file.c: __fget() and dup2() atomicity rules

On Mon, Jun 29, 2015 at 05:10:30PM +0200, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> __fget() makes sure a file refcount is not zero before
> taking a reference. It should also fetch again file pointer
> in order to respect dup2() atomicity requirements.
> 
> It should either read a NULL pointer or a file on which
> a refcount can be taken.

Hmm...   The problem is real, but I wonder if one could trigger a long
spin there...
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