* Qiang Huang | 2013-04-25 17:01:18 [+0800]:
So I looked again at this.
>This is revert of "sched-clear-pf-thread-bound-on-fallback-rq.patch"
>(commit 0d939066acdcb in v3.4-rt),.
>
>Select_fallback_rq() can be easilly called during system boot, because
>select_task_rq_fair() just return task_cpu(p) for bounded kernel threads,
>which is 0 during system boot and not in tsk_cpus_allowed, so
>select_fallback_rq() is called and PF_THREAD_BOUND is cleared. In my
>box, 1/3 bounded kernel threads will clear that flag after boot.
Please tell me _which_ threads lose this flag. I don't see this…
>And it will cause problems, for example:
># for pid in `ps -e -o pid`; do taskset -p -c 0-15 $pid; done
>this command will cause system hung.
I tracked this down and I grabbed a brown paper bag…
So to trigger this, it seems enough to
| taskset -p -c 5 2
| echo 0 > /sys/devices/system/cpu/cpu5/online
and the fix is:
Subject: [PATCH] kernel/cpu: fix cpu down problems
During forward porting I mixed up those two calls. The CPU up/down
worked usually. However a migrate_disable() in one of the notifier could
freeze the system.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
kernel/cpu.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index d44dea3..0784023 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -557,11 +557,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
}
cpu_hotplug_begin();
- err = cpu_unplug_begin(cpu);
- if (err) {
- printk("cpu_unplug_begin(%d) failed\n", cpu);
- goto out_cancel;
- }
err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
if (err) {
@@ -569,8 +564,16 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
__cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
printk("%s: attempt to take down CPU %u failed\n",
__func__, cpu);
+ goto out_cancel;
+ }
+
+ err = cpu_unplug_begin(cpu);
+ if (err) {
+ printk("cpu_unplug_begin(%d) failed\n", cpu);
+ __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
goto out_release;
}
+
smpboot_park_threads(cpu);
/* Notifiers are done. Don't let any more tasks pin this CPU. */
--
1.7.10.4
Does this fix your problems.
Sebastian
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