This is a note to let you know that I've just added the patch titled
sched/fair: Fix wrong negative conversion in find_energy_efficient_cpu()
to the 5.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-fair-fix-wrong-negative-conversion-in-find_ene.patch
and it can be found in the queue-5.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1c63dbec2b68963b66a50d9d3f82221fe31c9d1d
Author: Lukasz Luba <lukasz.luba@xxxxxxx>
Date: Mon Aug 10 09:30:04 2020 +0100
sched/fair: Fix wrong negative conversion in find_energy_efficient_cpu()
[ 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@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Link: https://lkml.kernel.org/r/20200810083004.26420-1-lukasz.luba@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1a68a0536adda..51408ebd76c27 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.
