Re: [PATCH] alios: sched: Fix race between runtime distribution and assignment

[kbuild test robot <lkp@intel.com>]

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Hi Huaixin,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tip/sched/core]
[also build test WARNING on tip/auto-latest linus/master linux/master v5.6-rc7 next-20200325]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Huaixin-Chang/alios-sched-Fix-race-between-runtime-distribution-and-assignment/20200326-064002
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 9c40365a65d62d7c06a95fb331b3442cb02d2fd9
config: openrisc-randconfig-a001-20200326 (attached as .config)
compiler: or1k-linux-gcc (GCC) 9.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=9.2.0 make.cross ARCH=openrisc 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

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/sched/fair.c: In function 'distribute_cfs_runtime':
>> kernel/sched/fair.c:4875:6: warning: 'remaining' may be used uninitialized in this function [-Wmaybe-uninitialized]
    4875 |   if (!remaining)
         |      ^

vim +/remaining +4875 kernel/sched/fair.c

671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4838  
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4839  static void distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4840  {
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4841  	struct cfs_rq *cfs_rq;
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4842  	u64 runtime, remaining;
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4843  	unsigned long flags;
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4844  
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4845  	rcu_read_lock();
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4846  	list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq,
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4847  				throttled_list) {
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4848  		struct rq *rq = rq_of(cfs_rq);
8a8c69c3277886 kernel/sched/fair.c Peter Zijlstra 2016-10-04  4849  		struct rq_flags rf;
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4850  
c0ad4aa4d8416a kernel/sched/fair.c Peter Zijlstra 2019-01-07  4851  		rq_lock_irqsave(rq, &rf);
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4852  		if (!cfs_rq_throttled(cfs_rq))
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4853  			goto next;
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4854  
5e2d2cc2588bd3 kernel/sched/fair.c Liangyan       2019-08-26  4855  		/* By the above check, this should never be true */
5e2d2cc2588bd3 kernel/sched/fair.c Liangyan       2019-08-26  4856  		SCHED_WARN_ON(cfs_rq->runtime_remaining > 0);
5e2d2cc2588bd3 kernel/sched/fair.c Liangyan       2019-08-26  4857  
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4858  		raw_spin_lock_irqsave(&cfs_b->lock, flags);
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4859  		runtime = -cfs_rq->runtime_remaining + 1;
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4860  		if (runtime > cfs_b->runtime)
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4861  			runtime = cfs_b->runtime;
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4862  		cfs_b->runtime -= runtime;
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4863  		remaining = cfs_b->runtime;
a340e0a2673eff kernel/sched/fair.c Huaixin Chang  2020-03-25  4864  		raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4865  
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4866  		cfs_rq->runtime_remaining += runtime;
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4867  
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4868  		/* we check whether we're throttled above */
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4869  		if (cfs_rq->runtime_remaining > 0)
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4870  			unthrottle_cfs_rq(cfs_rq);
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4871  
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4872  next:
c0ad4aa4d8416a kernel/sched/fair.c Peter Zijlstra 2019-01-07  4873  		rq_unlock_irqrestore(rq, &rf);
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4874  
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21 @4875  		if (!remaining)
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4876  			break;
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4877  	}
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4878  	rcu_read_unlock();
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4879  }
671fd9dabe5239 kernel/sched_fair.c Paul Turner    2011-07-21  4880  

:::::: The code at line 4875 was first introduced by commit
:::::: 671fd9dabe5239ad218c7eb48b2b9edee50250e6 sched: Add support for unthrottling group entities

:::::: TO: Paul Turner <pjt@google.com>
:::::: CC: Ingo Molnar <mingo@elte.hu>

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

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