Messages in this thread Patch in this message | | | From | Phil Auld <> | Subject | [PATCH] cpuhp: make target_store() a nop when target == state | Date | Mon, 23 May 2022 10:47:28 -0400 |
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writing the current state back into 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);
Make this safe by catching the case where target == state and bailing early.
Signed-off-by: Phil Auld <pauld@redhat.com> ---
Yeah, I know... don't do that. But it's still messy.
!< != >
kernel/cpu.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/kernel/cpu.c b/kernel/cpu.c index d0a9aa0b42e8..8a71b1149c60 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2302,6 +2302,9 @@ static ssize_t target_store(struct device *dev, struct device_attribute *attr, return -EINVAL; #endif + if (target == st->state) + return count; + ret = lock_device_hotplug_sysfs(); if (ret) return ret; -- 2.18.0
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