[PATCH RFC v6 13/16] io_uring/cmd: let cmds to know about dying task

[Bernd Schubert <bschubert@ddn.com>]

From: Pavel Begunkov <asml.silence@gmail.com>

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.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/linux/io_uring_types.h | 1 +
 io_uring/uring_cmd.c           | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 4b9ba523978d203ae23fb4ec9622d6e4e35a5e36..2ee5dc105b58ab48aef347a845509367a8241b9b 100644
--- a/include/linux/io_uring_types.h
+++ b/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 {
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 39c3c816ec7882b9aa26cd45df6ade531379e40f..38b6ccb4e55a1e85d204263272a280d3272557a4 100644
--- a/io_uring/uring_cmd.c
+++ b/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 (req->task->flags & PF_EXITING)
+		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,

-- 
2.43.0