Re: [syzbot] [io-uring?] [usb?] WARNING in io_get_cqe_overflow (2)

[Jens Axboe]

On 11/4/24 6:13 AM, Pavel Begunkov wrote:
> On 11/4/24 11:31, syzbot wrote:
>> syzbot has bisected this issue to:
>>
>> commit 3f1a546444738b21a8c312a4b49dc168b65c8706
>> Author: Jens Axboe <axboe@xxxxxxxxx>
>> Date:   Sat Oct 26 01:27:39 2024 +0000
>>
>>      io_uring/rsrc: get rid of per-ring io_rsrc_node list
>>
>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15aaa1f7980000
>> start commit:   c88416ba074a Add linux-next specific files for 20241101
>> git tree:       linux-next
>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=17aaa1f7980000
>> console output: https://syzkaller.appspot.com/x/log.txt?x=13aaa1f7980000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=704b6be2ac2f205f
>> dashboard link: https://syzkaller.appspot.com/bug?extid=e333341d3d985e5173b2
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16ec06a7980000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12c04740580000
>>
>> Reported-by: syzbot+e333341d3d985e5173b2@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Fixes: 3f1a54644473 ("io_uring/rsrc: get rid of per-ring io_rsrc_node list")
>>
>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 
> Previously all puts were done by requests, which in case of an exiting
> ring were fallback'ed to normal tw. Now, the unregister path posts CQEs,
> while the original task is still alive. Should be fine in general because
> at this point there could be no requests posting in parallel and all
> is synchronised, so it's a false positive, but we need to change the assert
> or something else.

Maybe something ala the below? Also changes these triggers to be
_once(), no point spamming them.

diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 00409505bf07..7792ed91469b 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -137,10 +137,11 @@ static inline void io_lockdep_assert_cq_locked(struct io_ring_ctx *ctx)
 		 * Not from an SQE, as those cannot be submitted, but via
 		 * updating tagged resources.
 		 */
-		if (ctx->submitter_task->flags & PF_EXITING)
-			lockdep_assert(current_work());
+		if (ctx->submitter_task->flags & PF_EXITING ||
+		    percpu_ref_is_dying(&ctx->refs))
+			lockdep_assert_once(current_work());
 		else
-			lockdep_assert(current == ctx->submitter_task);
+			lockdep_assert_once(current == ctx->submitter_task);
 	}
 #endif
 }

-- 
Jens Axboe