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

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Message-ID: <11fe65b8-eda4-121e-ec32-378b918d0909@gmail.com>
Date:   Tue, 1 Feb 2022 15:51:30 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     kgraul@...ux.ibm.com, davem@...emloft.net, kuba@...nel.org
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: [BUG] net: smc: possible deadlock in smc_lgr_free() and
 smc_link_down_work()

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.

I am not quite sure whether this possible problem is real and how to fix 
it if it is real.
Any feedback would be appreciated, thanks :)

Best wishes,
Jia-Ju Bai