io_uring/cmd: let cmds to know about dying task

When the taks that submitted a request is dying, a task work for that
request might get run by a kernel thread or even worse by a half
dismantled task. We can't just cancel the task work without running the
callback as the cmd might need to do some clean up, so pass a flag
instead. If set, it's not safe to access any task resources and the
callback is expected to cancel the cmd ASAP.

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: isilence

include/linux/io_uring_types.h

@@ -37,6 +37,7 @@ enum io_uring_cmd_flags {
 	/* set when uring wants to cancel a previously issued command */
 	IO_URING_F_CANCEL		= (1 << 11),
 	IO_URING_F_COMPAT		= (1 << 12),
+	IO_URING_F_TASK_DEAD		= (1 << 13),
 };
 
 struct io_wq_work_node {

io_uring/uring_cmd.c

@@ -119,9 +119,13 @@ EXPORT_SYMBOL_GPL(io_uring_cmd_mark_cancelable);
 static void io_uring_cmd_work(struct io_kiocb *req, struct io_tw_state *ts)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
+	unsigned int flags = IO_URING_F_COMPLETE_DEFER;
+
+	if (current->flags & (PF_EXITING | PF_KTHREAD))
+		flags |= IO_URING_F_TASK_DEAD;
 
 	/* task_work executor checks the deffered list completion */
-	ioucmd->task_work_cb(ioucmd, IO_URING_F_COMPLETE_DEFER);
+	ioucmd->task_work_cb(ioucmd, flags);
 }
 
 void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,