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block: Fix oops in locked_inode_to_wb_and_lock_list()

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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>
This commit is contained in:
Jan Kara
2017-03-23 01:37:00 +01:00
committed by Jens Axboe
parent b1c51afc00
commit f759741d9d
2 changed files with 3 additions and 6 deletions
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include/linux/writeback.h
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@@ -237,6 +237,7 @@ static inline void inode_attach_wb(struct inode *inode, struct page *page)
static inline void inode_detach_wb(struct inode *inode)
{
if (inode->i_wb) {
WARN_ON_ONCE(!(inode->i_state & I_CLEAR));
wb_put(inode->i_wb);
inode->i_wb = NULL;
}