Re: WARNING in io_fill_cqe_aux

[Pavel Begunkov <asml.silence@gmail.com>]

On 1/19/23 15:54, Jens Axboe wrote:
> On 1/19/23 4:37?AM, Xingyuan Mo wrote:
>> Hello,
>>
>> Recently, when using our tool to fuzz kernel, the following bug was
>> triggered.
>>
>> HEAD commit: 5dc4c995db9e Linux 6.2-rc4
>> git tree: mainline
>> compiler: gcc (Ubuntu 10.3.0-1ubuntu1~20.04) 10.3.0
>> kernel config: https://drive.google.com/file/d/1anGeZxcTgSKNZX4oywvsSfLqw1tcZSTp/view?usp=share_link
>> C reproducer: https://drive.google.com/file/d/1DxYuWGnFSBhqve-jjXloYhwKpyUm8nDt/view?usp=share_link
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: Xingyuan Mo <hdthky0@gmail.com>
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 1 PID: 36200 at io_uring/io_uring.h:108 io_get_cqe_overflow root/linux-6.2-rc4/io_uring/io_uring.h:108 [inline]
>> WARNING: CPU: 1 PID: 36200 at io_uring/io_uring.h:108 io_get_cqe root/linux-6.2-rc4/io_uring/io_uring.h:125 [inline]
>> WARNING: CPU: 1 PID: 36200 at io_uring/io_uring.h:108 io_fill_cqe_aux+0x69b/0x840 root/linux-6.2-rc4/io_uring/io_uring.c:832
>> Modules linked in:
>> CPU: 1 PID: 36200 Comm: syz-executor.0 Not tainted 6.2.0-rc4 #1
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
>> RIP: 0010:io_get_cqe_overflow root/linux-6.2-rc4/io_uring/io_uring.h:108 [inline]
>> RIP: 0010:io_get_cqe root/linux-6.2-rc4/io_uring/io_uring.h:125 [inline]
>> RIP: 0010:io_fill_cqe_aux+0x69b/0x840 root/linux-6.2-rc4/io_uring/io_uring.c:832
>> Code: fd 48 8d bb a8 00 00 00 be ff ff ff ff e8 dd 1b 02 06 31 ff 89 c5 89 c6 e8 c2 76 7e fd 85 ed 0f 85 44 fa ff ff e8 05 7a 7e fd <0f> 0b e9 38 fa ff ff e8 f9 79 7e fd 31 ff 89 ee e8 a0 76 7e fd 85
>> RSP: 0018:ffffc90015747b68 EFLAGS: 00010212
>> RAX: 000000000000016e RBX: ffff8881245b6000 RCX: ffffc90013881000
>> RDX: 0000000000040000 RSI: ffffffff8401f31b RDI: 0000000000000005
>> RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
>> R13: 0000000000000000 R14: 0000000000000000 R15: ffff8881245b6018
>> FS:  00007fcf02ab4700(0000) GS:ffff888135c00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000001b2e024000 CR3: 00000001054e6000 CR4: 0000000000752ee0
>> PKRU: 55555554
>> Call Trace:
>>   <TASK>
>>   __io_post_aux_cqe root/linux-6.2-rc4/io_uring/io_uring.c:880 [inline]
>>   io_post_aux_cqe+0x3b/0x90 root/linux-6.2-rc4/io_uring/io_uring.c:890
>>   io_msg_ring_data root/linux-6.2-rc4/io_uring/msg_ring.c:74 [inline]
>>   io_msg_ring+0x5b9/0xb70 root/linux-6.2-rc4/io_uring/msg_ring.c:227
>>   io_issue_sqe+0x6c2/0x1210 root/linux-6.2-rc4/io_uring/io_uring.c:1856
>>   io_queue_sqe root/linux-6.2-rc4/io_uring/io_uring.c:2028 [inline]
>>   io_submit_sqe root/linux-6.2-rc4/io_uring/io_uring.c:2286 [inline]
>>   io_submit_sqes+0x96c/0x1e10 root/linux-6.2-rc4/io_uring/io_uring.c:2397
>>   __do_sys_io_uring_enter+0xc20/0x2540 root/linux-6.2-rc4/io_uring/io_uring.c:3345
>>   do_syscall_x64 root/linux-6.2-rc4/arch/x86/entry/common.c:50 [inline]
>>   do_syscall_64+0x39/0xb0 root/linux-6.2-rc4/arch/x86/entry/common.c:80
>>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>> RIP: 0033:0x7fcf01c8f6cd
>> Code: c3 e8 17 32 00 00 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
>> RSP: 002b:00007fcf02ab3bf8 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
>> RAX: ffffffffffffffda RBX: 00007fcf01dbbf80 RCX: 00007fcf01c8f6cd
>> RDX: 0000000000000000 RSI: 0000000000007b84 RDI: 0000000000000004
>> RBP: 00007fcf01cfcb05 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
>> R13: 00007fcf01edfb2f R14: 00007fcf01edfcd0 R15: 00007fcf02ab3d80
>>   </TASK>
> 
> I think this should fix it. Pavel?

Looking that you added uring_lock locking, was the target
ring IOPOLL? If so sounds right and a comment below


> diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
> index 2d3cd945a531..c98e9c74054b 100644
> --- a/io_uring/msg_ring.c
> +++ b/io_uring/msg_ring.c
[...]
> +
>   void io_msg_ring_cleanup(struct io_kiocb *req)
>   {
>   	struct io_msg *msg = io_kiocb_to_cmd(req, struct io_msg);
> @@ -43,20 +65,25 @@ static void io_msg_tw_complete(struct callback_head *head)
>   	struct io_ring_ctx *target_ctx = req->file->private_data;
>   	int ret = 0;
>   
> -	if (current->flags & PF_EXITING)
> +	if (current->flags & PF_EXITING) {
>   		ret = -EOWNERDEAD;
> -	else if (!io_post_aux_cqe(target_ctx, msg->user_data, msg->len, 0))
> -		ret = -EOVERFLOW;
> +	} else {
> +		mutex_lock(&target_ctx->uring_lock);

It can be be conditional or could use a comment that it's only
necessary in case of IOPOLL ring.


> +		if (!io_post_aux_cqe(target_ctx, msg->user_data, msg->len, 0))
> +			ret = -EOVERFLOW;
> +		mutex_unlock(&target_ctx->uring_lock);
> +	}
>   
>   	if (ret < 0)
>   		req_set_fail(req);
>   	io_req_queue_tw_complete(req, ret);
>   }
>   

-- 
Pavel Begunkov