linux-kernel - Re: [PATCH v4 14/20] TP-futex: Support userspace reader/writer locks

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Date:   Fri, 30 Dec 2016 02:34:59 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Waiman Long <longman@...hat.com>
Cc:     kbuild-all@...org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Scott J Norton <scott.norton@....com>,
        Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v4 14/20] TP-futex: Support userspace reader/writer locks

Hi Waiman,

[auto build test WARNING on linus/master]
[also build test WARNING on v4.10-rc1 next-20161224]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Waiman-Long/futex-Introducing-throughput-optimized-TP-futexes/20161230-020021
config: i386-randconfig-x006-201652 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   kernel/futex.c: In function 'futex_lock':
>> kernel/futex.c:3776:13: warning: 'rspin_timeout' may be used uninitialized in this function [-Wmaybe-uninitialized]
        else if (curtime > rspin_timeout)
                ^
   kernel/futex.c:3656:6: note: 'rspin_timeout' was declared here
     u64 rspin_timeout;
         ^~~~~~~~~~~~~

vim +/rspin_timeout +3776 kernel/futex.c

  3760	
  3761				if (!owner_task && (reader_value >= 0)) {
  3762					int old_count = reader_value;
  3763	
  3764					/*
  3765					 * Reset timeout value if the old reader
  3766					 * count is 0 or the reader value changes and
  3767					 * handoff time hasn't been reached. Otherwise,
  3768					 * disable reader spinning if the handoff time
  3769					 * is reached.
  3770					 */
  3771					reader_value = (uval & FUTEX_TID_MASK);
  3772					if (!old_count || (!handoff_set
  3773						       && (reader_value != old_count)))
  3774						rspin_timeout = curtime +
  3775								TP_RSPIN_TIMEOUT;
> 3776					else if (curtime > rspin_timeout)
  3777						reader_value = -1;
  3778				}
  3779				if (!handoff_set && (curtime > handoff_time)) {
  3780					WARN_ON(READ_ONCE(state->handoff_pid));
  3781					WRITE_ONCE(state->handoff_pid, vpid);
  3782	
  3783					/*
  3784					 * Disable handoff check.

---
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