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Date: Fri, 9 Mar 2007 00:43:03 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "Michael K. Edwards" <medwards.linux@gmail.com>
Cc: "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: sys_write() racy for multi-threaded append?
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> Surely that's racy when two threads write to the same fd and the first
> vfs_write call blocks or is preempted.  Or does fget_light take some
> per-file lock that I'm not seeing?

I think you are making assumptions about file position behaviour that are
simply not guaranteed in the standards document.