ublk: don't issue uring_cmd from fallback task work

When ublk_ch_uring_cmd_cb() runs as fallback task work (e.g., because
the submitting task is exiting), the command should not be issued as
current is a kworker, not the daemon task. This can cause io->task
to capture the wrong task in __ublk_fetch(), leading to a task
mismatch warning in ublk_uring_cmd_cancel_fn().

Check tw.cancel and return -ECANCELED instead of issuing the command
from fallback context.

Fixes: 3421c7f ("ublk: make sure io cmd handled in submitter task context")
Signed-off-by: Ming Lei <[email protected]>

Author: axboe

drivers/block/ublk_drv.c

@@ -3496,8 +3496,10 @@ static void ublk_ch_uring_cmd_cb(struct io_tw_req tw_req, io_tw_token_t tw)
 {
 	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
 	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
-	int ret = ublk_ch_uring_cmd_local(cmd, issue_flags);
+	int ret = -ECANCELED;
 
+	if (!tw.cancel)
+		ret = ublk_ch_uring_cmd_local(cmd, issue_flags);
 	if (ret != -EIOCBQUEUED)
 		io_uring_cmd_done(cmd, ret, issue_flags);
 }