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Date: Mon, 29 Jun 2015 18:46:16 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>, Eric Dumazet <edumazet@google.com>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] fs/file.c: __fget() and dup2() atomicity rules
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On Mon, Jun 29, 2015 at 05:10:30PM +0200, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.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...