Re: [PATCH] sched/fair: sanitize vruntime of entity being placed

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

Hi Roman,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tip/sched/core]
[also build test WARNING on linus/master v6.2-rc5 next-20230127]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Roman-Kagan/sched-fair-sanitize-vruntime-of-entity-being-placed/20230128-130846
patch link:    https://lore.kernel.org/r/20230127163230.3339408-1-rkagan%40amazon.de
patch subject: [PATCH] sched/fair: sanitize vruntime of entity being placed
config: m68k-allyesconfig (https://download.01.org/0day-ci/archive/20230128/202301281410.4cvSCADA-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/2db31a18bcb88c280481672d7721f7e003d8df5a
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Roman-Kagan/sched-fair-sanitize-vruntime-of-entity-being-placed/20230128-130846
        git checkout 2db31a18bcb88c280481672d7721f7e003d8df5a
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash kernel/

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

All warnings (new ones prefixed by >>):

   kernel/sched/fair.c:688:5: warning: no previous prototype for 'sched_update_scaling' [-Wmissing-prototypes]
     688 | int sched_update_scaling(void)
         |     ^~~~~~~~~~~~~~~~~~~~
   kernel/sched/fair.c: In function 'place_entity':
>> kernel/sched/fair.c:4697:34: warning: integer overflow in expression of type 'long int' results in '-129542144' [-Woverflow]
    4697 |         if ((s64)sleep_time > 60 * NSEC_PER_SEC)
         |                                  ^


vim +4697 kernel/sched/fair.c

  4654	
  4655	static void
  4656	place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
  4657	{
  4658		u64 vruntime = cfs_rq->min_vruntime;
  4659		u64 sleep_time;
  4660	
  4661		/*
  4662		 * The 'current' period is already promised to the current tasks,
  4663		 * however the extra weight of the new task will slow them down a
  4664		 * little, place the new task so that it fits in the slot that
  4665		 * stays open at the end.
  4666		 */
  4667		if (initial && sched_feat(START_DEBIT))
  4668			vruntime += sched_vslice(cfs_rq, se);
  4669	
  4670		/* sleeps up to a single latency don't count. */
  4671		if (!initial) {
  4672			unsigned long thresh;
  4673	
  4674			if (se_is_idle(se))
  4675				thresh = sysctl_sched_min_granularity;
  4676			else
  4677				thresh = sysctl_sched_latency;
  4678	
  4679			/*
  4680			 * Halve their sleep time's effect, to allow
  4681			 * for a gentler effect of sleepers:
  4682			 */
  4683			if (sched_feat(GENTLE_FAIR_SLEEPERS))
  4684				thresh >>= 1;
  4685	
  4686			vruntime -= thresh;
  4687		}
  4688	
  4689		/*
  4690		 * Pull vruntime of the entity being placed to the base level of
  4691		 * cfs_rq, to prevent boosting it if placed backwards.  If the entity
  4692		 * slept for a long time, don't even try to compare its vruntime with
  4693		 * the base as it may be too far off and the comparison may get
  4694		 * inversed due to s64 overflow.
  4695		 */
  4696		sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start;
> 4697		if ((s64)sleep_time > 60 * NSEC_PER_SEC)
  4698			se->vruntime = vruntime;
  4699		else
  4700			se->vruntime = max_vruntime(se->vruntime, vruntime);
  4701	}
  4702	

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