• Eric Sandeen's avatar
    btrfs: use rcu_barrier() to wait for bdev puts at unmount · bc178622
    Eric Sandeen authored
    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.
    
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarEric Sandeen <sandeen@redhat.com>
    Signed-off-by: default avatarJosef Bacik <jbacik@fusionio.com>
    Signed-off-by: default avatarChris Mason <chris.mason@fusionio.com>
    bc178622
volumes.c 155 KB