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Date: Sun, 25 Feb 2001 19:40:42 -0500 (EST)
From: Alexander Viro <viro@math.psu.edu>
To: Jens Axboe <axboe@suse.de>
cc: Nate Eldredge <neldredge@hmc.edu>, linux-kernel@vger.kernel.org
Subject: Re: 2.4.2-ac3: loop threads in D state
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On Sun, 25 Feb 2001, Alexander Viro wrote:

> 
> 
> On Mon, 26 Feb 2001, Jens Axboe wrote:
> 
> > On Sun, Feb 25 2001, Alexander Viro wrote:
> > > Erm... Jens, it really should be
> > > 	if (atomic_dec_and_test(...))
> > > 		up(...);
> > > not just
> > > 	atomic_dec(...);
> > > 	up(...);
> > > 
> > > Otherwise you can end up with too early exit of loop_thread. Normally
> > > it would not matter, but in pathological cases...
> > 
> > How so? We dec it and up the semaphore, loop_thread runs until it's
> > done and ups lo_sem.
> 
> You are risking an extra up() here. Think what happens if you already had a
> pending request.

Let me elaborate: the race is very narrow and takes deliberate efforts to
hit. It _can_ be triggered, unfortunately. This extra up() will mess your
life later on.