[PATCH 6.6.y] block: skip sync_blockdev() on surprise removal in bdev_mark_dead()

[Chao Shi <coshi036@gmail.com>]

commit 49f06cff50a4ccf3b7a1a662ceb892b3b21a527a upstream.

bdev_mark_dead()'s @surprise == true means the device is already gone.
The filesystem callback fs_bdev_mark_dead() honours this and skips
sync_filesystem(), but the bare block device path (no ->mark_dead op)
lost its !surprise guard when the holder ->mark_dead callback was wired
up (see Fixes), and now calls sync_blockdev() unconditionally, which can
hang forever waiting on writeback that can no longer complete.

syzkaller hit this via nvme_reset_work()'s "I/O queues lost" path:
nvme_mark_namespaces_dead() -> blk_mark_disk_dead() ->
bdev_mark_dead(bdev, true) -> sync_blockdev() blocks in
folio_wait_writeback(), wedging the reset worker and every task waiting
on it.

Skip the sync on surprise removal, matching fs_bdev_mark_dead();
invalidate_bdev() still runs. Orderly removal (surprise == false) is
unchanged.

Found by FuzzNvme.

Fixes: d8530de5a6e8 ("block: call into the file system for bdev_mark_dead")
Acked-by: Sungwoo Kim <iam@sung-woo.kim>
Acked-by: Dave Tian <daveti@purdue.edu>
Acked-by: Weidong Zhu <weizhu@fiu.edu>
Signed-off-by: Chao Shi <coshi036@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260522220025.1770388-1-coshi036@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[ adjusted for 6.6.y: bdev_mark_dead() there still unlocks bd_holder_lock
  after the if/else and the else arm is a bare sync_blockdev(), so the
  !surprise guard is added as "else if (!surprise)" instead of inside the
  mainline else block. ]
Signed-off-by: Chao Shi <coshi036@gmail.com>
---
 block/bdev.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/bdev.c b/block/bdev.c
index f3b13aa1b7d4..2bbe0408dac2 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -961,7 +961,12 @@ void bdev_mark_dead(struct block_device *bdev, bool surprise)
 	mutex_lock(&bdev->bd_holder_lock);
 	if (bdev->bd_holder_ops && bdev->bd_holder_ops->mark_dead)
 		bdev->bd_holder_ops->mark_dead(bdev, surprise);
-	else
+	/*
+	 * On surprise removal the device is already gone; syncing is
+	 * futile and can hang forever waiting on I/O that will never
+	 * complete.  Match fs_bdev_mark_dead(), which also skips it.
+	 */
+	else if (!surprise)
 		sync_blockdev(bdev);
 	mutex_unlock(&bdev->bd_holder_lock);
 
-- 
2.43.0