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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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8
fs/block_dev.c
View File

@ -885,6 +885,8 @@ static void bdev_evict_inode(struct inode *inode)
spin_lock(&bdev_lock);
list_del_init(&bdev->bd_list);
spin_unlock(&bdev_lock);
/* Detach inode from wb early as bdi_put() may free bdi->wb */
inode_detach_wb(inode);
if (bdev->bd_bdi != &noop_backing_dev_info) {
bdi_put(bdev->bd_bdi);
bdev->bd_bdi = &noop_backing_dev_info;
@ -1875,12 +1877,6 @@ static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
kill_bdev(bdev);
bdev_write_inode(bdev);
/*
* Detaching bdev inode from its wb in __destroy_inode()
* is too late: the queue which embeds its bdi (along with
* root wb) can be gone as soon as we put_disk() below.
*/
inode_detach_wb(bdev->bd_inode);
}
if (bdev->bd_contains == bdev) {
if (disk->fops->release)

1
include/linux/writeback.h
View File

@ -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;
}