netdev - [BUG] net: ti: possible deadlock in cpts_ptp_gettimeex() and cpts_overflow

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Date:   Mon, 7 Feb 2022 22:43:03 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     davem@...emloft.net, kuba@...nel.org, grygorii.strashko@...com,
        vladimir.oltean@....com, vigneshr@...com, yangyingliang@...wei.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [BUG] net: ti: possible deadlock in cpts_ptp_gettimeex() and
 cpts_overflow_check()

Hello,

My static analysis tool reports a possible deadlock in the ti driver in 
Linux 5.16:

cpts_ptp_gettimeex()
   mutex_lock(&cpts->ptp_clk_mutex); --> Line 260 (Lock A)
   cpts_update_cur_time()
     wait_for_completion_timeout(&cpts->ts_push_complete, HZ); --> Line 
210 (Wait X)

cpts_overflow_check()
   mutex_lock(&cpts->ptp_clk_mutex); --> Line 411 (Lock A)
   cpts_update_cur_time()
     cpts_fifo_read()
       complete(&cpts->ts_push_complete); --> Line 142 (Wake X)

When cpts_ptp_gettimeex() is executed, "Wait X" is performed by holding 
"Lock A". If cpts_overflow_check() is executed at this time, "Wake X" 
cannot be performed to wake up "Wait X" in cpts_ptp_gettimeex(), because 
"Lock A" has been already hold by cpts_ptp_gettimeex(), causing a 
possible deadlock.
I find that "Wait X" is performed with a timeout, to relieve the 
possible deadlock; but I think this timeout can cause inefficient execution.

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