Commit 316319e8 authored Aug 19, 2021 by Jens Axboe

io_uring: add comments on why PF_EXITING checking is safe



We have two checks of task->flags & PF_EXITING left:

1) In io_req_task_submit(), which is called in task_work and hence always
   in the context of the original task. That means that
   req->task == current, and hence checking ->flags is totally fine.

2) In io_poll_rewait(), where we need to stop re-arming poll to prevent
   it interfering with cancelation. This is only run from task_work as
   well, and hence for this case too req->task == current.

Add a comment to both spots detailing that.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 79dca184

fs/io_uring.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -2112,6 +2112,7 @@ static void io_req_task_submit(struct io_kiocb *req)

		/* ctx stays valid until unlock, even if we drop all ours ctx->refs */
		mutex_lock(&ctx->uring_lock);
		/* req->task == current here, checking PF_EXITING is safe */
		if (likely(!(req->task->flags & PF_EXITING)))
		__io_queue_sqe(req);
		else
		@@ -4893,6 +4894,7 @@ static bool io_poll_rewait(struct io_kiocb req, struct io_poll_iocb poll)
		{
		struct io_ring_ctx *ctx = req->ctx;

		/* req->task == current here, checking PF_EXITING is safe */
		if (unlikely(req->task->flags & PF_EXITING))
		WRITE_ONCE(poll->canceled, true);