From: Lukasz Luba Date: Mon, 10 Aug 2020 08:30:04 +0000 (+0100) Subject: sched/fair: Fix wrong negative conversion in find_energy_efficient_cpu() X-Git-Tag: v5.15~2751^2~24 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=da0777d35f47892f359c3f73ea155870bb595700;p=platform%2Fkernel%2Flinux-starfive.git sched/fair: Fix wrong negative conversion in find_energy_efficient_cpu() 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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Link: https://lkml.kernel.org/r/20200810083004.26420-1-lukasz.luba@arm.com --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index abdb54e2..90ebaa4 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6594,7 +6594,8 @@ 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.