From: Muchun Song <songmuchun@bytedance.com>
Date: Wed, 7 Oct 2020 03:16:33 +0000 (+0800)
Subject: io_uring: Fix missing smp_mb() in io_cancel_async_work()
X-Git-Tag: v5.4.71~80
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=75524f753318f61bcf974a3062973aff3a40394d;p=users%2Fdwmw2%2Flinux.git

io_uring: Fix missing smp_mb() in io_cancel_async_work()

The store to req->flags and load req->work_task should not be
reordering in io_cancel_async_work(). We should make sure that
either we store REQ_F_CANCE flag to req->flags or we see the
req->work_task setted in io_sq_wq_submit_work().

Fixes: 1c4404efcf2c ("io_uring: make sure async workqueue is canceled on exit")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 33bd3ebdd3ef0..27770af20d240 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2247,6 +2247,12 @@ restart:
 
 		if (!ret) {
 			req->work_task = current;
+
+			/*
+			 * Pairs with the smp_store_mb() (B) in
+			 * io_cancel_async_work().
+			 */
+			smp_mb(); /* A */
 			if (req->flags & REQ_F_CANCEL) {
 				ret = -ECANCELED;
 				goto end_req;
@@ -3725,7 +3731,15 @@ static void io_cancel_async_work(struct io_ring_ctx *ctx,
 
 		req = list_first_entry(&ctx->task_list, struct io_kiocb, task_list);
 		list_del_init(&req->task_list);
-		req->flags |= REQ_F_CANCEL;
+
+		/*
+		 * The below executes an smp_mb(), which matches with the
+		 * smp_mb() (A) in io_sq_wq_submit_work() such that either
+		 * we store REQ_F_CANCEL flag to req->flags or we see the
+		 * req->work_task setted in io_sq_wq_submit_work().
+		 */
+		smp_store_mb(req->flags, req->flags | REQ_F_CANCEL); /* B */
+
 		if (req->work_task && (!files || req->files == files))
 			send_sig(SIGINT, req->work_task, 1);
 	}