Re: WARNING in io_fill_cqe_aux

[Jens Axboe <axboe@kernel.dk>]

On 1/19/23 10:31?AM, Pavel Begunkov wrote:
> 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

Right, this is for the target ring using IOPOLL.

>> 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.

I did mention that in the actual git commit message for it, but let's
add a comment as well. I initially figured it's not worth it making it
conditional, but it probably is since not a lot of folks would be using
IOPOLL anyway and sending messages. I'll make that tweak and post the
two patches I made out of this one.

-- 
Jens Axboe