From 316319e82f7342ef327223a23199648bfabeadcd Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 19 Aug 2021 09:41:42 -0600
Subject: [PATCH] io_uring: add comments on why PF_EXITING checking is safe
Git-commit: 316319e82f7342ef327223a23199648bfabeadcd
Patch-mainline: v5.15-rc1
References: bsc#1205205

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>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
 fs/io_uring.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 08546332f1b9..78aa4daf7969 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -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);
 
-- 
2.35.3