FAILED: patch "[PATCH] io_uring: fix io_prep_async_link locking" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 44eff40a32e8f5228ae041006352e32638ad2368 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <[email protected]>
Date: Mon, 26 Jul 2021 14:14:31 +0100
Subject: [PATCH] io_uring: fix io_prep_async_link locking

io_prep_async_link() may be called after arming a linked timeout, automatically making it unsafe to traverse the linked list. Guard with completion_lock if there was a linked timeout.

index 5a0fd6bcd318..c4d2b320cdd4 100644
@@ -1279,8 +1279,17 @@ static void io_prep_async_link(struct io_kiocb *req)
 {
 	struct io_kiocb *cur;
 
-	io_for_each_link(cur, req)
-		io_prep_async_work(cur);
+	if (req->flags & REQ_F_LINK_TIMEOUT) {
+		struct io_ring_ctx *ctx = req->ctx;
+
+		spin_lock_irq(&ctx->completion_lock);
+		io_for_each_link(cur, req)
+			io_prep_async_work(cur);
+		spin_unlock_irq(&ctx->completion_lock);
+	} else {
+		io_for_each_link(cur, req)
+			io_prep_async_work(cur);
+	}
 }
 
 static void io_queue_async_work(struct io_kiocb *req)