linux-kernel - Re: file offset corruption on 32-bit machines?

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Message-ID: <20080410151406.GA17051@shareable.org>
Date:	Thu, 10 Apr 2008 16:14:06 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Martin Mares <mj@....cz>
Cc:	Michal Hocko <mhocko@...e.cz>, Meelis Roos <mroos@...ux.ee>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: file offset corruption on 32-bit machines?

Martin Mares wrote:
> > [*] file_pos_{read,write} (fs/read_write.c) are not called under
> > lock (in sys_read, sys_write, ...), so even if f_pos is written
> > atomically, you will be able to get races when accessing shared
> > descriptor from different threads.
> 
> There are however cases when such behavior is perfectly valid: For example
> you can have a file of records of a fixed size, whose order does not matter.
> Then multiple processes can produce the records in parallel, sharing
> a single fd.

A rather more common thing:

Does this problem apply when appending lines or records to a log file,
with or without O_APPEND?

Also, can this problem affect programs doing concurrent reads/writes
using pread/pwrite (or the AIO equivalents)?

-- Jamie
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