On Tue, Apr 8, 2025 at 12:25 AM Ming Lei <ming.lei@xxxxxxxxxx> wrote:
>
> Commit 8284066946e6 ("ublk: grab request reference when the request is handled
> by userspace") doesn't grab request reference in case of recovery reissue.
> Then the request can be requeued & re-dispatch & failed when canceling
> uring command.
>
> If it is one zc request, the request can be freed before io_uring
> returns the zc buffer back, then cause kernel panic:
>
> [ 126.773061] BUG: kernel NULL pointer dereference, address: 00000000000000c8
> [ 126.773657] #PF: supervisor read access in kernel mode
> [ 126.774052] #PF: error_code(0x0000) - not-present page
> [ 126.774455] PGD 0 P4D 0
> [ 126.774698] Oops: Oops: 0000 [#1] SMP NOPTI
> [ 126.775034] CPU: 13 UID: 0 PID: 1612 Comm: kworker/u64:55 Not tainted 6.14.0_blk+ #182 PREEMPT(full)
> [ 126.775676] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-1.fc39 04/01/2014
> [ 126.776275] Workqueue: iou_exit io_ring_exit_work
> [ 126.776651] RIP: 0010:ublk_io_release+0x14/0x130 [ublk_drv]
>
> Fixes it by always grabbing request reference for aborting the request.
>
> Reported-by: Caleb Sander Mateos <csander@xxxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/linux-block/CADUfDZodKfOGUeWrnAxcZiLT+puaZX8jDHoj_sfHZCOZwhzz6A@xxxxxxxxxxxxxx/
> Fixes: 8284066946e6 ("ublk: grab request reference when the request is handled by userspace")
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> drivers/block/ublk_drv.c | 30 ++++++++++++++++++++++++++----
> 1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 2fd05c1bd30b..41bed67508f2 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -1140,6 +1140,25 @@ static void ublk_complete_rq(struct kref *ref)
> __ublk_complete_rq(req);
> }
>
> +static void ublk_do_fail_rq(struct request *req)
> +{
> + struct ublk_queue *ubq = req->mq_hctx->driver_data;
> +
> + if (ublk_nosrv_should_reissue_outstanding(ubq->dev))
> + blk_mq_requeue_request(req, false);
> + else
> + __ublk_complete_rq(req);
> +}
> +
> +static void ublk_fail_rq_fn(struct kref *ref)
> +{
> + struct ublk_rq_data *data = container_of(ref, struct ublk_rq_data,
> + ref);
> + struct request *req = blk_mq_rq_from_pdu(data);
> +
> + ublk_do_fail_rq(req);
> +}
> +
> /*
> * Since ublk_rq_task_work_cb always fails requests immediately during
> * exiting, __ublk_fail_req() is only called from abort context during
> @@ -1153,10 +1172,13 @@ static void __ublk_fail_req(struct ublk_queue *ubq, struct ublk_io *io,
> {
> WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_ACTIVE);
>
> - if (ublk_nosrv_should_reissue_outstanding(ubq->dev))
> - blk_mq_requeue_request(req, false);
> - else
> - ublk_put_req_ref(ubq, req);
> + if (ublk_need_req_ref(ubq)) {
> + struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
> +
> + kref_put(&data->ref, ublk_fail_rq_fn);
I think this looks good, just a small question. If __ublk_fail_req()
is called but there is at least 1 other reference, ublk_do_fail_rq()
won't get called here. When the last reference is dropped, it will
call __ublk_complete_rq() instead. That checks for io->flags &
UBLK_IO_FLAG_ABORTED and will terminate the I/O with BLK_STS_IOERR.
But is that the desired behavior in the
ublk_nosrv_should_reissue_outstanding() case? I would think it should
call blk_mq_requeue_request() instead.
Best,
Caleb
> + } else {
> + ublk_do_fail_rq(req);
> + }
> }
>
> static void ubq_complete_io_cmd(struct ublk_io *io, int res,
> --
> 2.47.0
>
