From: Chris Mason <chris.mason@fusionio.com>
To: Eric Sandeen <sandeen@redhat.com>
Cc: Chris Mason <clmason@fusionio.com>,
linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH] use rcu_barrier() to wait for bdev puts at unmount
Date: Sat, 9 Mar 2013 10:03:20 -0500 [thread overview]
Message-ID: <20130309150320.GB15521@shiny.masoncoding.com> (raw)
In-Reply-To: <513B4460.5090607@redhat.com>
On Sat, Mar 09, 2013 at 07:17:04AM -0700, Eric Sandeen wrote:
> On 3/9/13 6:27 AM, Chris Mason wrote:
> > On Fri, Mar 08, 2013 at 10:23:01PM -0700, Eric Sandeen wrote:
> >> Doing this would reliably fail with -EBUSY for me:
> >>
> >> # mount /dev/sdb2 /mnt/scratch; umount /mnt/scratch; mkfs.btrfs -f /dev/sdb2
> >> ...
> >> unable to open /dev/sdb2: Device or resource busy
> >>
> >> because mkfs.btrfs tries to open the device O_EXCL, and somebody still has it.
> >>
> >> Using systemtap to track bdev gets & puts shows a kworker thread doing a
> >> blkdev put after mkfs attempts a get; this is left over from the unmount.
> >>
> >> Adding an rcu_barrier() to btrfs_close_devices() causes unmount to wait
> >> until all blkdev_put()s are done, and the device is truly free once
> >> unmount completes.
> >
> > Thanks for tracking this down Eric.
>
> Sure thing, sorry it took so long.
>
> > Is this kworker triggered by btrfs
> > or is this something we should be doing for the other filesystems too?
>
> It's all btrfs ;)
>
> btrfs_close_devices
> __btrfs_close_devices
> call_rcu(&device->rcu, free_device);
> free_device
> INIT_WORK(&device->rcu_work, __free_device);
> schedule_work(&device->rcu_work);
>
Great, that makes a ton more sense. I'm a little confused on why we're
seeing it so much more now than in the past.
>
> The behavior came from:
>
> commit 1f78160ce1b1b8e657e2248118c4d91f881763f0
> Author: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
> Date: Wed Apr 20 10:09:16 2011 +0000
>
> Btrfs: using rcu lock in the reader side of devices list
>
> Anyway, I can send V2 in close_ctree if you like. Thinking about it more
> though, btrfs_close_devices is closer to the action, so now I think
> I'd leave it there. :)
>
> I probably should have put a comment in to say what the heck it's for,
> too. Feel free to fix on merge or I can send another patch.
Ok, please add the comment and a cc to stable. Thanks again.
-chris
next prev parent reply other threads:[~2013-03-09 15:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-09 5:23 [PATCH] use rcu_barrier() to wait for bdev puts at unmount Eric Sandeen
2013-03-09 12:27 ` Chris Mason
2013-03-09 14:17 ` Eric Sandeen
2013-03-09 15:03 ` Chris Mason [this message]
2013-03-09 15:18 ` [PATCH V2] btrfs: " Eric Sandeen
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