From: Eric Sandeen Date: Sat, 9 Mar 2013 15:18:39 +0000 (+0000) Subject: btrfs: use rcu_barrier() to wait for bdev puts at unmount X-Git-Tag: v3.2.41~2 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=2d8db10e98fca5bb13e70c3f35d7c0ff79df638c 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 Signed-off-by: Josef Bacik Signed-off-by: Chris Mason Signed-off-by: Ben Hutchings --- diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index d544035f6966..9899205bc430 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -577,6 +577,12 @@ 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; }