3.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Sandeen <sand...@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 <sand...@redhat.com>
Signed-off-by: Josef Bacik <jba...@fusionio.com>
Signed-off-by: Chris Mason <chris.ma...@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
fs/btrfs/volumes.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -681,6 +681,12 @@ 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;
}
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