linux-kernel - Re: [rcu:dev.2020.06.17a 35/38] kernel/sched/core.c:2650 try_to_wake

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Date:   Mon, 22 Jun 2020 14:27:08 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     kbuild@...ts.01.org, lkp@...el.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [rcu:dev.2020.06.17a 35/38] kernel/sched/core.c:2650
 try_to_wake_up() error: uninitialized symbol 'cpu'.

On Mon, Jun 22, 2020 at 03:11:17PM +0300, Dan Carpenter wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.06.17a
> head:   d3779e78b9848a707448dbb4a0cb6c4bb651fe9c
> commit: 59a5d883f2ccdce1700862b5983cfd3473630aea [35/38] EXP sched: Alleged fix for v5.8 merge-window scheduler issue
> config: x86_64-randconfig-m001-20200621 (attached as .config)
> compiler: gcc-9 (Debian 9.3.0-13) 9.3.0
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> 
> smatch warnings:
> kernel/sched/core.c:2650 try_to_wake_up() error: uninitialized symbol 'cpu'.
> 
> # https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?id=59a5d883f2ccdce1700862b5983cfd3473630aea
> git remote add rcu https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> git remote update rcu
> git checkout 59a5d883f2ccdce1700862b5983cfd3473630aea
> vim +/cpu +2650 kernel/sched/core.c
> 
> ^1da177e4c3f41 kernel/sched.c      Linus Torvalds 2005-04-16  2644  
> b5179ac70de85e kernel/sched/core.c Peter Zijlstra 2016-05-11  2645  	ttwu_queue(p, cpu, wake_flags);
> aacedf26fb7601 kernel/sched/core.c Peter Zijlstra 2019-06-07  2646  unlock:
> 013fdb8086acaa kernel/sched.c      Peter Zijlstra 2011-04-05  2647  	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> aacedf26fb7601 kernel/sched/core.c Peter Zijlstra 2019-06-07  2648  out:
> aacedf26fb7601 kernel/sched/core.c Peter Zijlstra 2019-06-07  2649  	if (success)
> aacedf26fb7601 kernel/sched/core.c Peter Zijlstra 2019-06-07 @2650  		ttwu_stat(p, cpu, wake_flags);
>                                                                                              ^^^
> This can be uninitialized on a couple "goto unlock;" paths.  Lines
> 2581 and 2622.  The KASan tool will warn about this at run time as well.
> I'm not sure why the build bot doesn't include the whole function for
> this bug report...

Indeed, lemme go fix.