Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 26/40] btrfs: use rcu_barrier() to wait for bdev puts at unmount | Date | Mon, 18 Mar 2013 14:11:04 -0700 |
| |
3.0-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Sandeen <sandeen@redhat.com>
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/btrfs/volumes.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -546,6 +546,12 @@ int btrfs_close_devices(struct btrfs_fs_ __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; }
| |