• NeilBrown's avatar
    block: destroy bdi before blockdev is unregistered. · 6cd18e71
    NeilBrown authored
    Because of the peculiar way that md devices are created (automatically
    when the device node is opened), a new device can be created and
    registered immediately after the
    	blk_unregister_region(disk_devt(disk), disk->minors);
    call in del_gendisk().
    
    Therefore it is important that all visible artifacts of the previous
    device are removed before this call.  In particular, the 'bdi'.
    
    Since:
    commit c4db59d3
    Author: Christoph Hellwig <hch@lst.de>
        fs: don't reassign dirty inodes to default_backing_dev_info
    
    moved the
       device_unregister(bdi->dev);
    call from bdi_unregister() to bdi_destroy() it has been quite easy to
    lose a race and have a new (e.g.) "md127" be created after the
    blk_unregister_region() call and before bdi_destroy() is ultimately
    called by the final 'put_disk', which must come after del_gendisk().
    
    The new device finds that the bdi name is already registered in sysfs
    and complains
    
    > [ 9627.630029] WARNING: CPU: 18 PID: 3330 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x5a/0x70()
    > [ 9627.630032] sysfs: cannot create duplicate filename '/devices/virtual/bdi/9:127'
    
    We can fix this by moving the bdi_destroy() call out of
    blk_release_queue() (which can happen very late when a refcount
    reaches zero) and into blk_cleanup_queue() - which happens exactly when the md
    device driver calls it.
    
    Then it is only necessary for md to call blk_cleanup_queue() before
    del_gendisk().  As loop.c devices are also created on demand by
    opening the device node, we make the same change there.
    
    Fixes: c4db59d3Reported-by: default avatarAzat Khuzhin <a3at.mail@gmail.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: stable@vger.kernel.org (v4.0)
    Signed-off-by: default avatarNeilBrown <neilb@suse.de>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
    6cd18e71
md.c 226 KB