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

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Message-ID: <OF861D7F24.6F60C82D-ON88257428.005C1DA4-88257428.005D5D80@us.ibm.com>
Date:	Fri, 11 Apr 2008 09:59:45 -0700
From:	Bryan Henderson <hbryan@...ibm.com>
To:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
Cc:	Bodo Eggert <7eggert@....de>, Diego Calleja <diegocg@...il.com>,
	Jan Kara <jack@...e.cz>, Jiri Kosina <jkosina@...e.cz>,
	linux-fsdevel@...r.kernel.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>, Meelis Roos <mroos@...ux.ee>
Subject: Re: file offset corruption on 32-bit machines?

>So if you write multithreaded code and don't understand what locking
>around shared resources is for, then your application might break.

I think I know what locking around shared resources is for, which is why 
I'm surprised the kernel doesn't do it.

Is it normal for a kernel resource not to be thread-safe (i.e. you don't 
get advertised/sensible results if two threads access it at the same 
time)?

>Can you give an example where locking is being used correctly where this 
can
>possibly fail?

I could accept (though I haven't thought about it) that there aren't any 
real-world applications that do simultaneous reads and writes through the 
same file pointer.  I might even accept that there can be no useful 
application that does.  But can you say such an application is incorrect?

--
Bryan Henderson                     IBM Almaden Research Center
San Jose CA                         Filesystems

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