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authorWill Deacon <will@kernel.org>2021-07-30 12:24:28 +0100
committerPeter Zijlstra <peterz@infradead.org>2021-08-20 12:32:58 +0200
commit9ae606bc74dd0e58d4de894e3c5cbb9d45599267 (patch)
treed3459bdb6258212fb8e17196a3fb518c71afebca /kernel/sched
parent304000390f88d049c85e9a0958ac5567f38816ee (diff)
sched: Introduce task_cpu_possible_mask() to limit fallback rq selection
Asymmetric systems may not offer the same level of userspace ISA support across all CPUs, meaning that some applications cannot be executed by some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do not feature support for 32-bit applications on both clusters. On such a system, we must take care not to migrate a task to an unsupported CPU when forcefully moving tasks in select_fallback_rq() in response to a CPU hot-unplug operation. Introduce a task_cpu_possible_mask() hook which, given a task argument, allows an architecture to return a cpumask of CPUs that are capable of executing that task. The default implementation returns the cpu_possible_mask, since sane machines do not suffer from per-cpu ISA limitations that affect scheduling. The new mask is used when selecting the fallback runqueue as a last resort before forcing a migration to the first active CPU. Signed-off-by: Will Deacon <will@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com> Reviewed-by: Quentin Perret <qperret@google.com> Link: https://lore.kernel.org/r/20210730112443.23245-2-will@kernel.org
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/core.c9
1 files changed, 3 insertions, 6 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7fa6ce74f40e..6f31267c4beb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2173,7 +2173,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
/* Non kernel threads are not allowed during either online or offline. */
if (!(p->flags & PF_KTHREAD))
- return cpu_active(cpu);
+ return cpu_active(cpu) && task_cpu_possible(cpu, p);
/* KTHREAD_IS_PER_CPU is always allowed. */
if (kthread_is_per_cpu(p))
@@ -3124,9 +3124,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
/* Look for allowed, online CPU in same node. */
for_each_cpu(dest_cpu, nodemask) {
- if (!cpu_active(dest_cpu))
- continue;
- if (cpumask_test_cpu(dest_cpu, p->cpus_ptr))
+ if (is_cpu_allowed(p, dest_cpu))
return dest_cpu;
}
}
@@ -3156,10 +3154,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
*
* More yuck to audit.
*/
- do_set_cpus_allowed(p, cpu_possible_mask);
+ do_set_cpus_allowed(p, task_cpu_possible_mask(p));
state = fail;
break;
-
case fail:
BUG();
break;