block: Fix oops in locked_inode_to_wb_and_lock_list()

When block device is closed, we call inode_detach_wb() in __blkdev_put()
which sets inode->i_wb to NULL. That is contrary to expectations that
inode->i_wb stays valid once set during the whole inode's lifetime and
leads to oops in wb_get() in locked_inode_to_wb_and_lock_list() because
inode_to_wb() returned NULL.

The reason why we called inode_detach_wb() is not valid anymore though.
BDI is guaranteed to stay along until we call bdi_put() from
bdev_evict_inode() so we can postpone calling inode_detach_wb() to that
moment.

Also add a warning to catch if someone uses inode_detach_wb() in a
dangerous way.

Reported-by: Thiago Jung Bauermann <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

0 files changed, 0 insertions, 0 deletions