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

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Message-ID: <f664c557-7924-4a75-a782-040cfc23f404@linux.ibm.com>
Date: Mon, 15 Apr 2024 19:37:06 +0200
From: Wenjia Zhang <wenjia@...ux.ibm.com>
To: Zhengchao Shao <shaozhengchao@...wei.com>, linux-s390@...r.kernel.org,
        netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com
Cc: 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



On 13.04.24 05:51, 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,

If I understand correctly, the sleeping issue is not the core issue, it 
looks like a kind of deadlock or kernel pointer dereference issue. Did 
you get crash? Do you have any backtrace? Why do you think the mutex 
lock will fix it?

Thanks,
Wenjia