Messages in this thread | | | Date | Wed, 25 May 2022 11:11:52 -0400 | From | Phil Auld <> | Subject | Re: [PATCH] cpuhp: make target_store() a nop when target == state |
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On Wed, May 25, 2022 at 04:09:29PM +0100 Valentin Schneider wrote: > On 25/05/22 09:31, Phil Auld wrote: > > On Wed, May 25, 2022 at 10:48:31AM +0100 Valentin Schneider wrote: > >> > >> Yeah it would be neater to not even enter cpu_{up, down}(), but my paranoia > >> makes me think we need the comparison to happen with at least the > >> cpu_add_remove_lock held to make sure st->state isn't moving under our > >> feet, otherwise we may still end up with target == state in _cpu_down() and > >> hit the bug you're describing. > >> > > > > This is what I was originally doing before I tried to "optimize" it: > > > > if (st->state < target) > > ret = cpu_up(dev->id, target); > > else if (st->state > target) > > ret = cpu_down(dev->id, target); > > > > This does the check under the lock and just falls through if state==target. > > I think I'll go back to that version. > > > > I also noticed while testing that the boot cpu does not get its target set. > > It's got state 233 but target 0. So reading that out and writing it back > > on offlines cpu0. I'll try to find where that is not getting set. > > > > If I had to guess I'd say it's because the boot CPU doesn't go through the > regular hotplug machinery and sets its state straight to CPUHP_ONLINE >
Yes, that was my thought.
> /me digs > > Maybe around this? > > void __init boot_cpu_hotplug_init(void) > { > this_cpu_write(cpuhp_state.booted_once, true); > this_cpu_write(cpuhp_state.state, CPUHP_ONLINE); > } >
Right, just found that too. Probably should set the target there as well.
Cheers, Phil
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