4.4-stable patches

added patches:
	sched-fair-handle-case-of-task_h_load-returning-0.patch

diff --git a/queue-4.4/sched-fair-handle-case-of-task_h_load-returning-0.patch b/queue-4.4/sched-fair-handle-case-of-task_h_load-returning-0.patch
new file mode 100644 (file)
index 0000000..bf9337e
--- /dev/null
+++ b/queue-4.4/sched-fair-handle-case-of-task_h_load-returning-0.patch
@@ -0,0 +1,55 @@
+From 01cfcde9c26d8555f0e6e9aea9d6049f87683998 Mon Sep 17 00:00:00 2001
+From: Vincent Guittot <vincent.guittot@linaro.org>
+Date: Fri, 10 Jul 2020 17:24:26 +0200
+Subject: sched/fair: handle case of task_h_load() returning 0
+
+From: Vincent Guittot <vincent.guittot@linaro.org>
+
+commit 01cfcde9c26d8555f0e6e9aea9d6049f87683998 upstream.
+
+task_h_load() can return 0 in some situations like running stress-ng
+mmapfork, which forks thousands of threads, in a sched group on a 224 cores
+system. The load balance doesn't handle this correctly because
+env->imbalance never decreases and it will stop pulling tasks only after
+reaching loop_max, which can be equal to the number of running tasks of
+the cfs. Make sure that imbalance will be decreased by at least 1.
+
+misfit task is the other feature that doesn't handle correctly such
+situation although it's probably more difficult to face the problem
+because of the smaller number of CPUs and running tasks on heterogenous
+system.
+
+We can't simply ensure that task_h_load() returns at least one because it
+would imply to handle underflow in other places.
+
+Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
+Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
+Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
+Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
+Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
+Cc: <stable@vger.kernel.org> # v4.4+
+Link: https://lkml.kernel.org/r/20200710152426.16981-1-vincent.guittot@linaro.org
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ kernel/sched/fair.c |   10 +++++++++-
+ 1 file changed, 9 insertions(+), 1 deletion(-)
+
+--- a/kernel/sched/fair.c
++++ b/kernel/sched/fair.c
+@@ -5939,7 +5939,15 @@ static int detach_tasks(struct lb_env *e
+               if (!can_migrate_task(p, env))
+                       goto next;
+ 
+-              load = task_h_load(p);
++              /*
++               * Depending of the number of CPUs and tasks and the
++               * cgroup hierarchy, task_h_load() can return a null
++               * value. Make sure that env->imbalance decreases
++               * otherwise detach_tasks() will stop only after
++               * detaching up to loop_max tasks.
++               */
++              load = max_t(unsigned long, task_h_load(p), 1);
++
+ 
+               if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
+                       goto next;

diff --git a/queue-4.4/series b/queue-4.4/series
index 88a9b1cee4b41bb7d2d648eeadb0f66da22434a3..9b6374c863c639b044b8aeb31d0359fc4df7f628 100644 (file)
--- a/queue-4.4/series
+++ b/queue-4.4/series
@@ -55,3 +55,4 @@ mips-fix-build-for-lts-kernel-caused-by-backporting-lpj-adjustment.patch
 hwmon-emc2103-fix-unable-to-change-fan-pwm1_enable-attribute.patch
 dmaengine-fsl-edma-fix-null-pointer-exception-in-fsl_edma_tx_handler.patch
 misc-atmel-ssc-lock-with-mutex-instead-of-spinlock.patch
+sched-fair-handle-case-of-task_h_load-returning-0.patch