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Date: Wed, 8 Apr 2015 17:03:25 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Ming Lei <ming.lei@canonical.com>
Cc: Jarod Wilson <jarod@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@infradead.org>, Jens Axboe <axboe@kernel.dk>,
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        Andrew Morton <akpm@linux-foundation.org>,
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	<nbd-general@lists.sourceforge.net>,
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Subject: Re: [PATCH 1/7] block: export blkdev_reread_part() and
 __blkdev_reread_part()
Message-ID: <20150408150325.GJ5029@twins.programming.kicks-ass.net>
References: <1428218688-4092-1-git-send-email-ming.lei@canonical.com>
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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);