linux-kernel - Re: [BUG] net: smc: possible deadlock in smc_lgr_free() and smc_link_down

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Message-ID: <fc2d73bb-a614-eb84-e635-31f8836f612a@linux.ibm.com>
Date:   Tue, 1 Feb 2022 11:53:54 +0100
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, davem@...emloft.net,
        kuba@...nel.org
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Wenjia Zhang <wenjia@...ux.ibm.com>
Subject: Re: [BUG] net: smc: possible deadlock in smc_lgr_free() and
 smc_link_down_work()

On 01/02/2022 08:51, Jia-Ju Bai wrote:
> Hello,
> 
> My static analysis tool reports a possible deadlock in the smc module in Linux 5.16:
> 
> smc_lgr_free()
>   mutex_lock(&lgr->llc_conf_mutex); --> Line 1289 (Lock A)
>   smcr_link_clear()
>     smc_wr_free_link()
>       wait_event(lnk->wr_tx_wait, ...); --> Line 648 (Wait X)
> 
> smc_link_down_work()
>   mutex_lock(&lgr->llc_conf_mutex); --> Line 1683 (Lock A)
>   smcr_link_down()
>     smcr_link_clear()
>       smc_wr_free_link()
>         smc_wr_wakeup_tx_wait()
>           wake_up_all(&lnk->wr_tx_wait); --> Line 78 (Wake X)
> 
> When smc_lgr_free() is executed, "Wait X" is performed by holding "Lock A". If smc_link_down_work() is executed at this time, "Wake X" cannot be performed to wake up "Wait X" in smc_lgr_free(), because "Lock A" has been already hold by smc_lgr_free(), causing a possible deadlock.
> 

Thank you for your reporting and the good description!

We will look into this issue and get back to you in a few days.