Messages in this thread Patch in this message | | | From | Phil Auld <> | Subject | [PATCH v4 1/2] cpuhp: make target_store() a nop when target == state | Date | Thu, 21 Jul 2022 10:28:51 -0400 |
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Writing the current state back in hotplug/target calls cpu_down() which will set cpu dying even when it isn't and then nothing will ever clear it. A stress test that reads values and writes them back for all cpu device files in sysfs will trigger the BUG() in select_fallback_rq once all cpus are marked as dying.
kernel/cpu.c::target_store() ... if (st->state < target) ret = cpu_up(dev->id, target); else ret = cpu_down(dev->id, target);
cpu_down() -> cpu_set_state() bool bringup = st->state < target; ... if (cpu_dying(cpu) != !bringup) set_cpu_dying(cpu, !bringup);
Fix this by letting state==target fall through in the target_store() conditional. Also make sure st->target == target in that case.
Signed-off-by: Phil Auld <pauld@redhat.com> Reviewed-by: Valentin Schneider <vschneid@redhat.com> --- kernel/cpu.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c index bbad5e375d3b..979de993f853 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2326,8 +2326,10 @@ static ssize_t target_store(struct device *dev, struct device_attribute *attr, if (st->state < target) ret = cpu_up(dev->id, target); - else + else if (st->state > target) ret = cpu_down(dev->id, target); + else if (WARN_ON(st->target != target)) + st->target = target; out: unlock_device_hotplug(); return ret ? ret : count; -- 2.31.1
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