linux-kernel - Re: sys_write() racy for multi-threaded append?

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Message-ID: <20070309004303.721f8b50@lxorguk.ukuu.org.uk>
Date:	Fri, 9 Mar 2007 00:43:03 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"Michael K. Edwards" <medwards.linux@...il.com>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: sys_write() racy for multi-threaded append?

> 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.
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