linux-kernel - Re: [PATCH 1/7] block: export blkdev_reread_part() and __blkdev_reread

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Message-ID: <20150408152748.GJ14217@redhat.com>
Date:	Wed, 8 Apr 2015 11:27:48 -0400
From:	Jarod Wilson <jarod@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ming Lei <ming.lei@...onical.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Markus Pargmann <mpa@...gutronix.de>,
	Stefan Weinhuber <wein@...ibm.com>,
	Stefan Haberland <stefan.haberland@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Fabian Frederick <fabf@...net.be>,
	David Herrmann <dh.herrmann@...il.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"nbd-general@...ts.sourceforge.net" 
	<nbd-general@...ts.sourceforge.net>, linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/7] block: export blkdev_reread_part() and
 __blkdev_reread_part()

On Wed, Apr 08, 2015 at 05:03:25PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 08, 2015 at 10:50:56PM +0800, Ming Lei wrote:
> > > +/*
> > > + * This is an exported API for the block driver, and will not
> > > + * acquire bd_mutex, leaving it up to the caller to handle
> > > + * any necessary locking.
> > 
> > Actually, the function is introduced and should be used in case
> > that bd_mutex has been held already, such as clearing fd in
> > loop release().
> > 
> > > + */
> > > +int __blkdev_reread_part(struct block_device *bdev)
> > >  {
> > >         struct gendisk *disk = bdev->bd_disk;
> > >
> 
> 	lockdep_assert_held(&bdev->bd_mutex);
> 
> is an excellent means of avoiding that comment and verifying its
> actually true :-)

Ah, yes, that was actually suggested by Christoph as well, I was too hasty
shoving something back out the door on multiple counts.

> > > + */
> > > +int blkdev_reread_part(struct block_device *bdev)
> > > +{
> > > +       int res;
> > > +
> > >         if (!mutex_trylock(&bdev->bd_mutex))
> > >                 return -EBUSY;
> 
> Is that really needed? It seems rather poor form.

It goes away later in the series and gets converted to a straight
mutex_lock().

-- 
Jarod Wilson
jarod@...hat.com

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