In ublk_queue_rq(), Assume current request is a re-issued request aborted
previously in monitor_work because the ubq_daemon(ioucmd's task) is
PF_EXITING. For this request, we cannot call
io_uring_cmd_complete_in_task() anymore because at that moment io_uring
context may be freed in case that no inflight ioucmd exists. Otherwise,
we may cause null-deref in ctx->fallback_work.
Add a check on UBLK_IO_FLAG_ABORTED to prevent the above situation. This
check is safe and makes sense.
Note: monitor_work sets UBLK_IO_FLAG_ABORTED and ends this request
(releasing the tag). Then the request is restarted(allocating the tag)
and we are here. Since releasing/allocating a tag implies smp_mb(),
finding UBLK_IO_FLAG_ABORTED guarantees that here is a re-issued request
aborted previously.
Suggested-by: Ming Lei <ming.lei@xxxxxxxxxx>
Signed-off-by: ZiyangZhang <ZiyangZhang@xxxxxxxxxxxxxxxxx>
---
drivers/block/ublk_drv.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 685a43b7ae6e..6a4a94b4cdf4 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -756,9 +756,25 @@ static blk_status_t ublk_queue_rq(struct blk_mq_hw_ctx *hctx,
if (task_work_add(ubq->ubq_daemon, &data->work, notify_mode))
goto fail;
} else {
- struct io_uring_cmd *cmd = ubq->ios[rq->tag].cmd;
+ struct ublk_io *io = &ubq->ios[rq->tag];
+ struct io_uring_cmd *cmd = io->cmd;
struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
+ /*
+ * If the check pass, we know that this is a re-issued request aborted
+ * previously in monitor_work because the ubq_daemon(cmd's task) is
+ * PF_EXITING. We cannot call io_uring_cmd_complete_in_task() anymore
+ * because this ioucmd's io_uring context may be freed now if no inflight
+ * ioucmd exists. Otherwise we may cause null-deref in ctx->fallback_work.
+ *
+ * Note: monitor_work sets UBLK_IO_FLAG_ABORTED and ends this request(releasing
+ * the tag). Then the request is re-started(allocating the tag) and we are here.
+ * Since releasing/allocating a tag implies smp_mb(), finding UBLK_IO_FLAG_ABORTED
+ * guarantees that here is a re-issued request aborted previously.
+ */
+ if ((io->flags & UBLK_IO_FLAG_ABORTED))
+ goto fail;
+
pdu->req = rq;
io_uring_cmd_complete_in_task(cmd, ublk_rq_task_work_cb);
}
--
2.27.0
