cpusets, hotplug, scheduler: fix scheduler domain breakage
Commit f18f982ab ("sched: CPU hotplug events must not destroy scheduler
domains created by the cpusets") introduced a hotplug-related problem as
described below:
Upon CPU_DOWN_PREPARE,
update_sched_domains() -> detach_destroy_domains(&cpu_online_map)
does the following:
/*
* Force a reinitialization of the sched domains hierarchy. The domains
* and groups cannot be updated in place without racing with the balancing
* code, so we temporarily attach all running cpus to the NULL domain
* which will prevent rebalancing while the sched domains are recalculated.
*/
The sched-domains should be rebuilt when a CPU_DOWN ops. has been
completed, effectively either upon CPU_DEAD{_FROZEN} (upon success) or
CPU_DOWN_FAILED{_FROZEN} (upon failure -- restore the things to their
initial state). That's what update_sched_domains() also does but only
for !CPUSETS case.
With f18f982ab, sched-domains' reinitialization is delegated to
CPUSETS code:
cpuset_handle_cpuhp() -> common_cpu_mem_hotplug_unplug() ->
rebuild_sched_domains()
Being called for CPU_UP_PREPARE and if its callback is called after
update_sched_domains()), it just negates all the work done by
update_sched_domains() -- i.e. a soon-to-be-offline cpu is included in
the sched-domains and that makes it visible for the load-balancer
while the CPU_DOWN ops. is in progress.
__migrate_live_tasks() moves the tasks off a 'dead' cpu (it's already
"offline" when this function is called).
try_to_wake_up() is called for one of these tasks from another CPU ->
the load-balancer (wake_idle()) picks up a "dead" CPU and places the
task on it. Then e.g. BUG_ON(rq->nr_running) detects this a bit later
-> oops.
Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Tested-by: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Paul Menage <menage@google.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: miaox@cn.fujitsu.com
Cc: rostedt@goodmis.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 9fceb97..798b3ab 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1882,7 +1882,7 @@
* in order to minimize text size.
*/
-static void common_cpu_mem_hotplug_unplug(void)
+static void common_cpu_mem_hotplug_unplug(int rebuild_sd)
{
cgroup_lock();
@@ -1894,7 +1894,8 @@
* Scheduler destroys domains on hotplug events.
* Rebuild them based on the current settings.
*/
- rebuild_sched_domains();
+ if (rebuild_sd)
+ rebuild_sched_domains();
cgroup_unlock();
}
@@ -1912,11 +1913,22 @@
static int cpuset_handle_cpuhp(struct notifier_block *unused_nb,
unsigned long phase, void *unused_cpu)
{
- if (phase == CPU_DYING || phase == CPU_DYING_FROZEN)
+ switch (phase) {
+ case CPU_UP_CANCELED:
+ case CPU_UP_CANCELED_FROZEN:
+ case CPU_DOWN_FAILED:
+ case CPU_DOWN_FAILED_FROZEN:
+ case CPU_ONLINE:
+ case CPU_ONLINE_FROZEN:
+ case CPU_DEAD:
+ case CPU_DEAD_FROZEN:
+ common_cpu_mem_hotplug_unplug(1);
+ break;
+ default:
return NOTIFY_DONE;
+ }
- common_cpu_mem_hotplug_unplug();
- return 0;
+ return NOTIFY_OK;
}
#ifdef CONFIG_MEMORY_HOTPLUG
@@ -1929,7 +1941,7 @@
void cpuset_track_online_nodes(void)
{
- common_cpu_mem_hotplug_unplug();
+ common_cpu_mem_hotplug_unplug(0);
}
#endif
