| From 4bdd996273a8396a3c796e196dfb4c386a17b2ef Mon Sep 17 00:00:00 2001 |
| From: Eric Sandeen <sandeen@redhat.com> |
| Date: Sat, 9 Mar 2013 15:18:39 +0000 |
| Subject: [PATCH] btrfs: use rcu_barrier() to wait for bdev puts at unmount |
| |
| 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 |
| |