[tip: sched/urgent] sched/topology, cpuset: Account for housekeeping CPUs to avoid empty cpumasks

["tip-bot2 for Valentin Schneider" <tip-bot2@linutronix.de>]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     48a723d23b0d957e5b5861b974864e53c6841de8
Gitweb:        https://git.kernel.org/tip/48a723d23b0d957e5b5861b974864e53c6841de8
Author:        Valentin Schneider <valentin.schneider@arm.com>
AuthorDate:    Mon, 04 Nov 2019 00:39:06 
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 15 Nov 2019 11:02:20 +01:00

sched/topology, cpuset: Account for housekeeping CPUs to avoid empty cpumasks

Michal noted that a cpuset's effective_cpus can be a non-empy mask, but
because of the masking done with housekeeping_cpumask(HK_FLAG_DOMAIN)
further down the line, we can still end up with an empty cpumask being
passed down to partition_sched_domains_locked().

Do the proper thing and don't just check the mask is non-empty - check
that its intersection with housekeeping_cpumask(HK_FLAG_DOMAIN) is
non-empty.

Reported-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dietmar.Eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hannes@cmpxchg.org
Cc: lizefan@huawei.com
Cc: morten.rasmussen@arm.com
Cc: qperret@google.com
Cc: tj@kernel.org
Cc: vincent.guittot@linaro.org
Fixes: cd1cb3350561 ("sched/topology: Don't try to build empty sched domains")
Link: https://lkml.kernel.org/r/20191104003906.31476-1-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/cgroup/cpuset.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index c87ee64..e4c1078 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -798,8 +798,14 @@ static int generate_sched_domains(cpumask_var_t **domains,
 		    cpumask_subset(cp->cpus_allowed, top_cpuset.effective_cpus))
 			continue;
 
+		/*
+		 * Skip cpusets that would lead to an empty sched domain.
+		 * That could be because effective_cpus is empty, or because
+		 * it's only spanning CPUs outside the housekeeping mask.
+		 */
 		if (is_sched_load_balance(cp) &&
-		    !cpumask_empty(cp->effective_cpus))
+		    cpumask_intersects(cp->effective_cpus,
+				       housekeeping_cpumask(HK_FLAG_DOMAIN)))
 			csa[csn++] = cp;
 
 		/* skip @cp's subtree if not a partition root */