linux-kernel - Re: [PATCH] rdma_rxe: call comp_handler without holding cq->cq

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Message-ID: <6dbc1383-0c9f-4648-ae8d-4219e89589f4@gmail.com>
Date: Wed, 13 Aug 2025 00:54:06 +0900
From: Daisuke Matsuda <dskmtsd@...il.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>,
 Philipp Reisner <philipp.reisner@...bit.com>
Cc: Zhu Yanjun <zyjzyj2000@...il.com>, Jason Gunthorpe <jgg@...pe.ca>,
 Leon Romanovsky <leon@...nel.org>, linux-rdma@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rdma_rxe: call comp_handler without holding cq->cq_lock

On 2025/08/11 22:48, Zhu Yanjun wrote:
> 在 2025/8/10 22:26, Philipp Reisner 写道:
>> On Thu, Aug 7, 2025 at 3:09 AM Zhu Yanjun <yanjun.zhu@...ux.dev> wrote:
>>>
>>> 在 2025/8/6 5:39, Philipp Reisner 写道:
>>>> Allow the comp_handler callback implementation to call ib_poll_cq().
>>>> A call to ib_poll_cq() calls rxe_poll_cq() with the rdma_rxe driver.
>>>> And rxe_poll_cq() locks cq->cq_lock. That leads to a spinlock deadlock.
>>>>
>>>> The Mellanox and Intel drivers allow a comp_handler callback
>>>> implementation to call ib_poll_cq().
>>>>
>>>> Avoid the deadlock by calling the comp_handler callback without
>>>> holding cq->cw_lock.
>>>>
>>>> Signed-off-by: Philipp Reisner <philipp.reisner@...bit.com>
>>>
>>> ERROR: test_resize_cq (tests.test_cq.CQTest.test_resize_cq)
>>> Test resize CQ, start with specific value and then increase and decrease
>>> ----------------------------------------------------------------------
>>> Traceback (most recent call last):
>>>     File "/root/deb/rdma-core/tests/test_cq.py", line 135, in test_resize_cq
>>>       u.poll_cq(self.client.cq)
>>>     File "/root/deb/rdma-core/tests/utils.py", line 687, in poll_cq
>>>       wcs = _poll_cq(cq, count, data)
>>>             ^^^^^^^^^^^^^^^^^^^^^^^^^
>>>     File "/root/deb/rdma-core/tests/utils.py", line 669, in _poll_cq
>>>       raise PyverbsError(f'Got timeout on polling ({count} CQEs remaining)')
>>> pyverbs.pyverbs_error.PyverbsError: Got timeout on polling (1 CQEs
>>> remaining)
>>>
>>> After I applied your patch in kervel v6.16, I got the above errors.
>>>
>>> Zhu Yanjun
>>>
>>
>> Hello Zhu,
>>
>> When I run the test_resize_cq test in a loop (100 runs each) on the
>> original code and with my patch, I get about the same failure rate.
> 
> Add Daisuke Matsuda
> 
> If I remember it correctly, when Daisuke and I discussed ODP patches, we both made tests with rxe, from our tests results, it seems that this test_resize_cq error does not occur.

Hi Zhu and Philipp,

As far as I know, this error has been present for some time.
It might be possible to investigate further by capturing a memory dump while the polling is stuck, but I have not had time to do that yet.
At least, I can confirm that this is not a regression caused by Philipp's patch.

Thanks,
Daisuke