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

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Message-ID: <CADGDV=UgDb51nEtdide7k8==urCdrWcig8kBAY6k0PryR0c7xw@mail.gmail.com>
Date: Mon, 11 Aug 2025 07:26:29 +0200
From: Philipp Reisner <philipp.reisner@...bit.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
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 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.

without my patch success=87 failure=13
without my patch success=82 failure=18
without my patch success=81 failure=19
with my patch    success=89 failure=11
with my patch    success=90 failure=10
with my patch    success=82 failure=18

The patch I am proposing does not change the failure rate of this test.

Best regards,
 Philipp

#!/bin/bash

success=0
failure=0

for (( i = 0; i < 100; i++ )) do
      if rdma-core/build/bin/run_tests.py -k test_resize_cq; then
  success=$((success+1))
      else
  failure=$((failure+1))
      fi
done
echo success=$success failure=$failure