block: Fix oops in locked_inode_to_wb_and_lock_list()
authorJan Kara <jack@suse.cz>
Thu, 23 Mar 2017 00:37:00 +0000 (01:37 +0100)
committerJens Axboe <axboe@fb.com>
Thu, 23 Mar 2017 02:11:33 +0000 (20:11 -0600)
commitf759741d9d913eb57784a94b9bca78b376fc26a9
tree19832434e2c4c1db34bceee048f422b910300686
parentb1c51afc00f164457e126dcfc946fdd563948d26
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 <bauerman@linux.vnet.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
fs/block_dev.c
include/linux/writeback.h