linux-kernel - Re: [PATCH 1/6] block: export blkdev_reread

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Message-ID: <20150406134843.GF14217@redhat.com>
Date:	Mon, 6 Apr 2015 09:48:43 -0400
From:	Jarod Wilson <jarod@...hat.com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Jens Axboe <axboe@...nel.dk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	David Herrmann <dh.herrmann@...il.com>,
	Markus Pargmann <mpa@...gutronix.de>,
	"nbd-general@...ts.sourceforge.net" 
	<nbd-general@...ts.sourceforge.net>,
	Stefan Haberland <stefan.haberland@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Fabian Frederick <fabf@...net.be>, linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/6] block: export blkdev_reread_part()

On Mon, Apr 06, 2015 at 09:42:27AM -0400, Jarod Wilson wrote:
> On Mon, Apr 06, 2015 at 12:40:12AM +0800, Ming Lei wrote:
> > On Mon, Apr 6, 2015 at 12:12 AM, Christoph Hellwig <hch@...radead.org> wrote:
> > >> +/*
> > >> + * This is exported as API for block driver, can be called
> > >> + * with requiring bd_mutex or not.
> > >> + */
> > >> +int __blkdev_reread_part(struct block_device *bdev, bool lock)
> > >>  {
> > >>       struct gendisk *disk = bdev->bd_disk;
> > >>       int res;
> > >> @@ -159,12 +163,14 @@ static int blkdev_reread_part(struct block_device *bdev)
> > >>               return -EINVAL;
> > >>       if (!capable(CAP_SYS_ADMIN))
> > >>               return -EACCES;
> > >> -     if (!mutex_trylock(&bdev->bd_mutex))
> > >> +     if (lock && !mutex_trylock(&bdev->bd_mutex))
> > >>               return -EBUSY;
> > >
> > > Please don't add funtions that do conditional locking, instead move
> > > all the code into blkdev_reread_part_nolock, and then wrap it:
> > >
> > > int blkdev_reread_part(struct block_device *bdev)
> > > {
> > >         if (!mutex_trylock(&bdev->bd_mutex))
> > >                 return -EBUSY;
> > >         blkdev_reread_part_nolock(bdev);
> > >         mutex_unlock(&bdev->bd_mutex);
> > > }
> > 
> > Yes, it is more clean, but with extra acquiring lock cost for the
> > failure cases, especially when we replace trylock with mutex_lock().
> 
> I was working on a version of this myself over the past few days, I
> actually removed blkdev_reread_part() entirely, renamed
> fs/partition-generic.c::reread_partitions() to __reread_partitions(), then

Sorry, that was block/partition-generic.c, not fs/.

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

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