From: Lukasz Luba lukasz.luba@arm.com
[ Upstream commit da0777d35f47892f359c3f73ea155870bb595700 ]
In find_energy_efficient_cpu() 'cpu_cap' could be less that 'util'. It might be because of RT, DL (so higher sched class than CFS), irq or thermal pressure signal, which reduce the capacity value. In such situation the result of 'cpu_cap - util' might be negative but stored in the unsigned long. Then it might be compared with other unsigned long when uclamp_rq_util_with() reduced the 'util' such that is passes the fits_capacity() check.
Prevent this situation and make the arithmetic more safe.
Fixes: 1d42509e475cd ("sched/fair: Make EAS wakeup placement consider uclamp restrictions") Signed-off-by: Lukasz Luba lukasz.luba@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Valentin Schneider valentin.schneider@arm.com Link: https://lkml.kernel.org/r/20200810083004.26420-1-lukasz.luba@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6b3b59cc51d6c..f71e8b0e0346a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6586,7 +6586,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
util = cpu_util_next(cpu, p, cpu); cpu_cap = capacity_of(cpu); - spare_cap = cpu_cap - util; + spare_cap = cpu_cap; + lsub_positive(&spare_cap, util);
/* * Skip CPUs that cannot satisfy the capacity request.