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

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Date:	Wed, 8 Apr 2015 17:03:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Jarod Wilson <jarod@...hat.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 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 :-)

> >         if (!disk_part_scan_enabled(disk) || bdev != bdev->bd_contains)
> >                 return -EINVAL;
> >         if (!capable(CAP_SYS_ADMIN))
> >                 return -EACCES;
> > +
> > +       return rescan_partitions(disk, bdev);
> > +}
> > +EXPORT_SYMBOL(__blkdev_reread_part);
> > +
> > +/*
> > + * This is an exported API for the block driver, and will
> > + * acquire bd_mutex. Make sure you aren't calling it with
> > + * bd_mutex already held, or we'll return -EBUSY.
> 
> Strictly speaking, it should be "Make sure you aren't calling it
> with bd_mutex already held in current context".
> 
> > + */
> > +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.

> > -       res = rescan_partitions(disk, bdev);
> > +       res = __blkdev_reread_part(bdev);
> >         mutex_unlock(&bdev->bd_mutex);
> > +
> >         return res;
> >  }
> > +EXPORT_SYMBOL(blkdev_reread_part);
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