Messages in this thread | | | Date | Tue, 19 Jul 2022 11:03:10 -0400 | From | Phil Auld <> | Subject | Re: [PATCH v3 1/2] cpuhp: make target_store() a nop when target == state |
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On Tue, Jul 19, 2022 at 03:34:03PM +0100 Valentin Schneider wrote: > On 11/07/22 17:16, Phil Auld wrote: > > 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> > > One nit below, otherwise: > Reviewed-by: Valentin Schneider <vschneid@redhat.com> >
Thanks!
> > --- > > kernel/cpu.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/cpu.c b/kernel/cpu.c > > index bbad5e375d3b..305694a2ca26 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 (st->target != target) > > Should we make this: > > else if (WARN(st->target != target)) >
If you think that's important I can make it a WARN, sure.
I'll try to remember to keep your Reviewed-bys this time if that's okay.
Cheers, Phil
> > + st->target = target; > > out: > > unlock_device_hotplug(); > > return ret ? ret : count; > > -- > > 2.31.1 >
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