netdev - Re: [PATCH net] net/smc: fix potential sleeping issue in smc_switch

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Date: Wed, 17 Apr 2024 16:29:56 +0800
From: shaozhengchao <shaozhengchao@...wei.com>
To: Guangguan Wang <guangguan.wang@...ux.alibaba.com>,
	<linux-s390@...r.kernel.org>, <netdev@...r.kernel.org>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>
CC: <wenjia@...ux.ibm.com>, <jaka@...ux.ibm.com>, <alibuda@...ux.alibaba.com>,
	<tonylu@...ux.alibaba.com>, <guwen@...ux.alibaba.com>,
	<weiyongjun1@...wei.com>, <yuehaibing@...wei.com>,
	<tangchengchang@...wei.com>
Subject: Re: [PATCH net] net/smc: fix potential sleeping issue in
 smc_switch_conns


Hi Guangguan:
   Thank you for your review. When I used the hns driver, I ran into the
problem of "scheduling while atomic". But the problem was tested on the
5.10 kernel branch, and I'm still trying to reproduce it using the
mainline.

Zhengchao Shao

On 2024/4/17 16:00, Guangguan Wang wrote:
> 
> 
> On 2024/4/13 11:51, Zhengchao Shao wrote:
>> Potential sleeping issue exists in the following processes:
>> smc_switch_conns
>>    spin_lock_bh(&conn->send_lock)
>>    smc_switch_link_and_count
>>      smcr_link_put
>>        __smcr_link_clear
>>          smc_lgr_put
>>            __smc_lgr_free
>>              smc_lgr_free_bufs
>>                __smc_lgr_free_bufs
>>                  smc_buf_free
>>                    smcr_buf_free
>>                      smcr_buf_unmap_link
>>                        smc_ib_put_memory_region
>>                          ib_dereg_mr
>>                            ib_dereg_mr_user
>>                              mr->device->ops.dereg_mr
>> If scheduling exists when the IB driver implements .dereg_mr hook
>> function, the bug "scheduling while atomic" will occur. For example,
>> cxgb4 and efa driver. Use mutex lock instead of spin lock to fix it.
>>
>> Fixes: 20c9398d3309 ("net/smc: Resolve the race between SMC-R link access and clear")
>> Signed-off-by: Zhengchao Shao <shaozhengchao@...wei.com>
>> ---
>>   net/smc/af_smc.c   |  2 +-
>>   net/smc/smc.h      |  2 +-
>>   net/smc/smc_cdc.c  | 14 +++++++-------
>>   net/smc/smc_core.c |  8 ++++----
>>   net/smc/smc_tx.c   |  8 ++++----
>>   5 files changed, 17 insertions(+), 17 deletions(-)
>>
> 
> Hi Zhengchao,
> 
> I doubt whether this bug really exists, as efa supports SRD QP while SMC-R relies on RC QP,
> cxgb4 is a IWARP adaptor while SMC-R relies on ROCE adaptor.
> 
> Thanks,
> Guangguan Wang