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Date: Sat, 3 Mar 2001 15:13:37 -0500 (EST)
From: Alexander Viro <viro@math.psu.edu>
To: Jens Axboe <axboe@suse.de>
cc: agrawal@ais.org, linux-kernel@vger.kernel.org
Subject: Re: lingering loopback bugs?
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On Sat, 3 Mar 2001, Jens Axboe wrote:

> On Sat, Mar 03 2001, Alexander Viro wrote:
> > > Look for the patch I posted yesterday (hint: just remove these two
> > > lines from loop_end_io_transfer)
> > > 
> > >                if (atomic_dec_and_test(&lo->lo_pending))
> > >                        up(&lo->lo_bh_mutex);
> > 
> > Uhh... And what will compensate for atomic_inc() in loop_make_request() in
> > case of loop over block device?
> 
> There is no atomic_inc() in loop_make_request, I moved it to
> count pending bh on the queue only. But hmm, we should not
> be able to remove it while it has bhs in flight. Ok, I'll
> rearrange this a bit again...

Notice that up() is triggered _only_ on the clr_fd() - until then
->lo_pending is at least 1. Lo_rundown is exactly that - mode when
we've already given that barrier up and just wait for the last
guy to up that semaphore while loop_thread queue is empty. Which
will make loop_thread terminate.

	BTW, I think I see a possible problem. How about replacing
atomic_dec() in loop_thread with
		if (atomic_dec_and_test(...))
			break;
to handle the case where we have pending requests at the clr_fd time
and the last one happens to be in the queue?
							Cheers,
								Al

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