| From | Paul Gortmaker <> | Subject | [v2.6.34-stable 184/213] btrfs: use rcu_barrier() to wait for bdev puts at unmount | Date | Wed, 5 Feb 2014 15:02:19 -0500 |
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From: Eric Sandeen <sandeen@redhat.com>
------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. -------------------
commit bc178622d40d87e75abc131007342429c9b03351 upstream.
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 path:
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);
so unmount might complete before __free_device fires & does its blkdev_put.
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.
Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com> Signed-off-by: Chris Mason <chris.mason@fusionio.com> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> --- fs/btrfs/volumes.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index c04ebb1e4c98..7f75546941ac 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -565,6 +565,12 @@ int btrfs_close_devices(struct btrfs_fs_devices *fs_devices) __btrfs_close_devices(fs_devices); free_fs_devices(fs_devices); } + /* + * Wait for rcu kworkers under __btrfs_close_devices + * to finish all blkdev_puts so device is really + * free when umount is done. + */ + rcu_barrier(); return ret; } -- 1.8.5.2
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