The ->bd_queue member of struct block_device was added in commit
87192a2a49c4 ("vfs: cache request_queue in struct block_device") in
v3.3. However, blk_get_backing_dev_info() has been using
bdev_get_queue() and grabbing the request_queue through the gendisk
since before the git era.
At final __blkdev_put() time ->bd_disk is cleared while ->bd_queue is
not. The queue remains valid until the final put of the parent disk.
The following crash signature results from blk_get_backing_dev_info()
trying to lookup the queue through ->bd_disk after the final put of the
block device. Simply switch bdev_get_queue() to use ->bd_queue directly
which is guaranteed to still be valid since the request_queue is alive
as long as the inode corresponding to the bdev has not been destroyed.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000568
IP: blk_get_backing_dev_info+0x10/0x20
[..]
Call Trace:
__inode_attach_wb+0x3a7/0x5d0
__filemap_fdatawrite_range+0xf8/0x100
filemap_write_and_wait+0x40/0x90
fsync_bdev+0x54/0x60
? bdget_disk+0x30/0x40
invalidate_partition+0x24/0x50
del_gendisk+0xfa/0x230
Cc: Jan Kara <j...@suse.cz>
Cc: Jens Axboe <ax...@fb.com>
Cc: Jeff Moyer <jmo...@redhat.com>
Cc: Christoph Hellwig <h...@lst.de>
Cc: Wei Fang <fangw...@huawei.com>
Cc: Rabin Vincent <rab...@axis.com>
Cc: Andi Kleen <a...@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
block/blk-core.c | 4 ++--
include/linux/blkdev.h | 6 +++++-
2 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index e8713137b846..cfd6731dfed7 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -108,8 +108,8 @@ void blk_queue_congestion_threshold(struct request_queue *q)
* @bdev: device
*
* Locates the passed device's request queue and returns the address of its
- * backing_dev_info. This function can only be called if @bdev is opened
- * and the return value is never NULL.
+ * backing_dev_info. This function can be called until the final iput()
+ * of the bdev inode.
*/
struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
{
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c47c358ba052..fd332da0fc38 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -841,7 +841,11 @@ bool blk_poll(struct request_queue *q, blk_qc_t cookie);
static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
{
- return bdev->bd_disk->queue; /* this is never NULL */
+ /*
+ * ->bd_queue is valid as long as there is a reference against
+ * the bdev inode.
+ */
+ return bdev->bd_queue;
}
/*
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