Commit 365bb9cc authored Mar 23, 2017 by Jan Kara Committed by Ritesh Harjani Oct 18, 2017

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>
Change-Id: I119244bd6cc425e9b18dd3189f3c9f45dc0f6f77
Git-repo:
git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git


Git-commit: f759741d9d913eb57784a94b9bca78b376fc26a9
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>

parent f4f6d3c0

fs/block_dev.c

+2 −6

Original line number	Diff line number	Diff line
		@@ -558,6 +558,8 @@ static void bdev_evict_inode(struct inode *inode)
		}
		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;
		@@ -1547,12 +1549,6 @@ 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)

include/linux/writeback.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -224,6 +224,7 @@ 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;
		}