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commitc258f5c450upstream. When one process(such as udev) opens ublk block device (e.g., to read the partition table via bdev_open()), a deadlock[1] can occur: 1. bdev_open() grabs disk->open_mutex 2. The process issues read I/O to ublk backend to read partition table 3. In __ublk_complete_rq(), blk_update_request() or blk_mq_end_request() runs bio->bi_end_io() callbacks 4. If this triggers fput() on file descriptor of ublk block device, the work may be deferred to current task's task work (see fput() implementation) 5. This eventually calls blkdev_release() from the same context 6. blkdev_release() tries to grab disk->open_mutex again 7. Deadlock: same task waiting for a mutex it already holds The fix is to run blk_update_request() and blk_mq_end_request() with bottom halves disabled. This forces blkdev_release() to run in kernel work-queue context instead of current task work context, and allows ublk server to make forward progress, and avoids the deadlock. Fixes:71f28f3136("ublk_drv: add io_uring based userspace block driver") Link: https://github.com/ublk-org/ublksrv/issues/170 [1] Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Caleb Sander Mateos <csander@purestorage.com> [axboe: rewrite comment in ublk] Signed-off-by: Jens Axboe <axboe@kernel.dk> [ The fix omits the change in __ublk_do_auto_buf_reg() since this function doesn't exist in Linux 6.12. ] Signed-off-by: Alva Lan <alvalan9@foxmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>