linux-kernel - Re: [PATCH] amiflop: get rid of sleep

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Message-ID: <20081210004810.GA5073@infernal.debian.net>
Date:	Wed, 10 Dec 2008 01:48:10 +0100
From:	Andreas Bombe <aeb@...ian.org>
To:	Joerg Dorchain <joerg@...chain.net>
Cc:	linux-m68k@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] amiflop: get rid of sleep_on calls

On Tue, Dec 09, 2008 at 09:26:08AM +0100, Joerg Dorchain wrote:
> On Mon, Dec 08, 2008 at 04:59:38PM +0000, Andreas Bombe wrote:
> > The replacement for the unconditional sleep_on() in fd_motor_on() is a
> > complete_all() together with a INIT_COMPLETION() before the mod_timer()
> > call.  It appears to me that fd_motor_on() might be called concurrently
> > and fd_select() does not guarantee mutual exclusivity in the case the
> > same drive gets selected again.
> 
> Selecting the same drive repeatly does not matter. The selected
> drive is the one the next command or transfer applies to.

I think we're not talking about the same problem.  If I were to use
complete() together with wait_for_completion() there would be a problem
if fd_motor_on() can get as far as wait_for_completion() while a
previous completion is yet uncompleted.  This can not happen for
different drives, as the fd_select() would block.  If it could happen
for the same drive, the complete() would allow only one task to
continue.  The complete_all() takes care of that.

If requests are serialized for a drive so that there won't ever be two
running at the same time for certain (thinking about it, it's probable),
I could make it a simple complete().  It's hardly worth the risk,
however.
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