Messages in this thread | | | Date | Wed, 20 Jan 2021 15:17:24 +0000 | From | Vincent Donnefort <> | Subject | Re: [PATCH 2/4] cpu/hotplug: CPUHP_BRINGUP_CPU exception in fail injection |
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On Wed, Jan 20, 2021 at 01:58:35PM +0100, Peter Zijlstra wrote: > On Mon, Jan 11, 2021 at 05:10:45PM +0000, vincent.donnefort@arm.com wrote: > > From: Vincent Donnefort <vincent.donnefort@arm.com> > > > > The atomic states (between CPUHP_AP_IDLE_DEAD and CPUHP_AP_ONLINE) are > > triggered by the CPUHP_BRINGUP_CPU step. If the latter doesn't run, none > > of the atomic can. Hence, rollback is not possible after a hotunplug > > CPUHP_BRINGUP_CPU step failure and the "fail" interface shouldn't allow > > it. Moreover, the current CPUHP_BRINGUP_CPU teardown callback > > (finish_cpu()) cannot fail anyway. > > > > Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com> > > --- > > kernel/cpu.c | 9 +++++++-- > > 1 file changed, 7 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/cpu.c b/kernel/cpu.c > > index 9121edf..bcd7b2a 100644 > > --- a/kernel/cpu.c > > +++ b/kernel/cpu.c > > @@ -2216,9 +2216,14 @@ static ssize_t write_cpuhp_fail(struct device *dev, > > return -EINVAL; > > > > /* > > - * Cannot fail STARTING/DYING callbacks. > > + * Cannot fail STARTING/DYING callbacks. Also, those callbacks are > > + * triggered by BRINGUP_CPU bringup callback. Therefore, the latter > > + * can't fail during hotunplug, as it would mean we have no way of > > + * rolling back the atomic states that have been previously teared > > + * down. > > */ > > - if (cpuhp_is_atomic_state(fail)) > > + if (cpuhp_is_atomic_state(fail) || > > + (fail == CPUHP_BRINGUP_CPU && st->state > CPUHP_BRINGUP_CPU)) > > return -EINVAL; > > Should we instead disallow failing any state that has .cant_stop ?
We would reduce the scope of what can be tested: bringup_cpu() and takedown_cpu() are both marked as "cant_stop". Still, those callbacks are allowed to fail.
Checking for cant_stop, made me also see that write_cpuhp_target() is probably missing a check for cpuhp_is_atomic_state(). For the same reason as this patch, when doing cpu_down(), we can't stop in one of these states.
-- Vincent
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