FAILED: patch "[PATCH] io_uring: lock overflowing for IOPOLL" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-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]>.

Possible dependencies:

544d163d659d ("io_uring: lock overflowing for IOPOLL") a8cf95f93610 ("io_uring: fix overflow handling regression") fa18fa2272c7 ("io_uring: inline __io_req_complete_put()") f9d567c75ec2 ("io_uring: inline __io_req_complete_post()")

thanks,

greg k-h

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

From 544d163d659d45a206d8929370d5a2984e546cb7 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <[email protected]>
Date: Thu, 12 Jan 2023 13:08:56 +0000
Subject: [PATCH] io_uring: lock overflowing for IOPOLL
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

syzbot reports an issue with overflow filling for IOPOLL:

WARNING: CPU: 0 PID: 28 at io_uring/io_uring.c:734 io_cqring_event_overflow+0x1c0/0x230 io_uring/io_uring.c:734
CPU: 0 PID: 28 Comm: kworker/u4:1 Not tainted 6.2.0-rc3-syzkaller-16369-g358a161a6a9e #0
Workqueue: events_unbound io_ring_exit_work
Call trace:
 io_cqring_event_overflow+0x1c0/0x230 io_uring/io_uring.c:734
 io_req_cqe_overflow+0x5c/0x70 io_uring/io_uring.c:773
 io_fill_cqe_req io_uring/io_uring.h:168 [inline]
 io_do_iopoll+0x474/0x62c io_uring/rw.c:1065
 io_iopoll_try_reap_events+0x6c/0x108 io_uring/io_uring.c:1513
 io_uring_try_cancel_requests+0x13c/0x258 io_uring/io_uring.c:3056
 io_ring_exit_work+0xec/0x390 io_uring/io_uring.c:2869
 process_one_work+0x2d8/0x504 kernel/workqueue.c:2289
 worker_thread+0x340/0x610 kernel/workqueue.c:2436
 kthread+0x12c/0x158 kernel/kthread.c:376
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:863

There is no real problem for normal IOPOLL as flush is also called with uring_lock taken, but it's getting more complicated for IOPOLL|SQPOLL, for which __io_cqring_overflow_flush() happens from the CQ waiting path.

index 8227af2e1c0f..9c3ddd46a1ad 100644
@@ -1062,7 +1062,11 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 			continue;
 
 		req->cqe.flags = io_put_kbuf(req, 0);
-		io_fill_cqe_req(req->ctx, req);
+		if (unlikely(!__io_fill_cqe_req(ctx, req))) {
+			spin_lock(&ctx->completion_lock);
+			io_req_cqe_overflow(req);
+			spin_unlock(&ctx->completion_lock);
+		}
 	}
 
 	if (unlikely(!nr_events))

Here's this one.

Jens Axboe

From b800a0647421fc4c4aca538a9f0bc5bfceaece65 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <[email protected]>
Date: Sat, 14 Jan 2023 08:41:33 -0700
Subject: [PATCH 1/2] io_uring: lock overflowing for IOPOLL
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit 544d163d659d45a206d8929370d5a2984e546cb7 upstream.

syzbot reports an issue with overflow filling for IOPOLL:

WARNING: CPU: 0 PID: 28 at io_uring/io_uring.c:734 io_cqring_event_overflow+0x1c0/0x230 io_uring/io_uring.c:734
CPU: 0 PID: 28 Comm: kworker/u4:1 Not tainted 6.2.0-rc3-syzkaller-16369-g358a161a6a9e #0
Workqueue: events_unbound io_ring_exit_work
Call trace:
 io_cqring_event_overflow+0x1c0/0x230 io_uring/io_uring.c:734
 io_req_cqe_overflow+0x5c/0x70 io_uring/io_uring.c:773
 io_fill_cqe_req io_uring/io_uring.h:168 [inline]
 io_do_iopoll+0x474/0x62c io_uring/rw.c:1065
 io_iopoll_try_reap_events+0x6c/0x108 io_uring/io_uring.c:1513
 io_uring_try_cancel_requests+0x13c/0x258 io_uring/io_uring.c:3056
 io_ring_exit_work+0xec/0x390 io_uring/io_uring.c:2869
 process_one_work+0x2d8/0x504 kernel/workqueue.c:2289
 worker_thread+0x340/0x610 kernel/workqueue.c:2436
 kthread+0x12c/0x158 kernel/kthread.c:376
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:863

There is no real problem for normal IOPOLL as flush is also called with uring_lock taken, but it's getting more complicated for IOPOLL|SQPOLL, for which __io_cqring_overflow_flush() happens from the CQ waiting path.

---
 io_uring/rw.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

index bb47cc4da713..6223472095d2 100644
@@ -1055,7 +1055,11 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 			continue;
 
 		req->cqe.flags = io_put_kbuf(req, 0);
-		__io_fill_cqe_req(req->ctx, req);
+		if (unlikely(!__io_fill_cqe_req(ctx, req))) {
+			spin_lock(&ctx->completion_lock);
+			io_req_cqe_overflow(req);
+			spin_unlock(&ctx->completion_lock);
+		}
 	}
 
 	if (unlikely(!nr_events))

2.39.0