sched/deadline: Fix inter- exclusive cpusets migrations

Users can perform clustered scheduling using the cpuset facility.
After an exclusive cpuset is created, task migrations happen only
between CPUs belonging to the same cpuset. Inter- cpuset migrations
can only happen when the user requires so, moving a task between
different cpusets. This behaviour is broken in SCHED_DEADLINE, as
currently spurious inter- cpuset migration may happen without user
intervention.

This patch fix the problem (and shuffles the code a bit to improve
clarity).

Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: raistlin@linux.it
Cc: michael@amarulasolutions.com
Cc: fchecconi@gmail.com
Cc: daniel.wagner@bmw-carit.de
Cc: vincent@legout.info
Cc: luca.abeni@unitn.it
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1411118561-26323-4-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 8 insertions, 3 deletions

diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index bd95963dae80..539ca3ce071b 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -107,9 +107,7 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
         int best_cpu = -1;
         const struct sched_dl_entity *dl_se = &p->dl;
 
-        if (later_mask && cpumask_and(later_mask, cp->free_cpus,
-                        &p->cpus_allowed) && cpumask_and(later_mask,
-                        later_mask, cpu_active_mask)) {
+        if (later_mask && cpumask_and(later_mask, later_mask, cp->free_cpus)) {
                 best_cpu = cpumask_any(later_mask);
                 goto out;
         } else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index efb94124420d..abfaf3d9a29f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1164,6 +1164,13 @@ static int find_later_rq(struct task_struct *task)
         if (task->nr_cpus_allowed == 1)
                 return -1;
 
+        /*
+         * We have to consider system topology and task affinity
+         * first, then we can look for a suitable cpu.
+         */
+        cpumask_copy(later_mask, task_rq(task)->rd->span);
+        cpumask_and(later_mask, later_mask, cpu_active_mask);
+        cpumask_and(later_mask, later_mask, &task->cpus_allowed);
         best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
                         task, later_mask);
         if (best_cpu == -1)