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Date: Mon, 22 Oct 2018 13:20:16 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Hans Petter Selasky <hps@selasky.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: Re: svn commit: r339582 - head/sys/dev/sound/midi
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On Mon, Oct 22, 2018 at 12:09:54PM +0200, Hans Petter Selasky wrote:
> On 10/22/18 11:51 AM, Konstantin Belousov wrote:
> > On Mon, Oct 22, 2018 at 08:58:28AM +0000, Hans Petter Selasky wrote:
> >> Author: hselasky
> >> Date: Mon Oct 22 08:58:27 2018
> >> New Revision: 339582
> >> URL: https://svnweb.freebsd.org/changeset/base/339582
> >>
> >> Log:
> >>    Drop sequencer mutex around uiomove() and make sure we don't move more bytes
> >>    than is available, else a panic might happen.
> > And why it is safe to drop the mutex ?
> > If it is safe to drop, why do you need the mutex at all ?
> > 
> 
> The seq mutex protects the queue state, which is entirely computed prior 
> or after uiomove().

Then why do you need to re-acquire the mutex after uiomove ?