Re: [PATCH] SCSI: Fix some locking issues

[Jens Axboe <jens.axboe@oracle.com>]

On Wed, Jul 02 2008, James Bottomley wrote:
> On Wed, 2008-07-02 at 13:50 +0200, Jens Axboe wrote:
> > On Wed, Jul 02 2008, Elias Oltmanns wrote:
> > > > The blk_plug_queue change looks reasonable ... however, blk_plug_queue
> > > > itself looks like it might not entirely need the queue lock ... I need
> > > > to investigate more closely.
> > > 
> > > Well, I rather think it does. We have to serialise access to the
> > > unplug_timer and there is a call to __set_bit() which, as I understand,
> > > requires the calling function to ensure atomicity.
> > 
> > Yep, blk_plug_device() needs to be called with the queue lock held.
> 
> That's what the comment says ... but if you replaced the test_bit with
> an atomic operation then the rest of it does look to be in no need of
> serialisation ... unless there's something I missed?

Indeed, but then you would have to use atomic bitops everywhere and that
is the bit we moved away from.

-- 
Jens Axboe