[BUG] net: smc: possible deadlock in smc_lgr_free() and smc_link_down_work()

[Jia-Ju Bai <baijiaju1990@gmail.com>]

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