Messages in this thread | | | Subject | Re: [PATCH v2] padata: validate cpumask without removed CPU during offline | From | Daniel Jordan <> | Date | Thu, 22 Aug 2019 18:10:30 -0400 |
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On 8/21/19 11:50 PM, Herbert Xu wrote: > On Fri, Aug 09, 2019 at 05:06:03PM -0400, Daniel Jordan wrote: >> diff --git a/kernel/padata.c b/kernel/padata.c >> index d056276a96ce..01460ea1d160 100644 >> --- a/kernel/padata.c >> +++ b/kernel/padata.c >> @@ -702,10 +702,7 @@ static int __padata_remove_cpu(struct padata_instance *pinst, int cpu) >> struct parallel_data *pd = NULL; >> >> if (cpumask_test_cpu(cpu, cpu_online_mask)) { >> - >> - if (!padata_validate_cpumask(pinst, pinst->cpumask.pcpu) || >> - !padata_validate_cpumask(pinst, pinst->cpumask.cbcpu)) >> - __padata_stop(pinst); >> + __padata_stop(pinst); >> >> pd = padata_alloc_pd(pinst, pinst->cpumask.pcpu, >> pinst->cpumask.cbcpu); >> @@ -716,6 +713,9 @@ static int __padata_remove_cpu(struct padata_instance *pinst, int cpu) >> >> cpumask_clear_cpu(cpu, pd->cpumask.cbcpu); >> cpumask_clear_cpu(cpu, pd->cpumask.pcpu); >> + if (padata_validate_cpumask(pinst, pd->cpumask.pcpu) && >> + padata_validate_cpumask(pinst, pd->cpumask.cbcpu)) >> + __padata_start(pinst); >> } > > I looked back at the original code and in fact the original > assumption is to call this after cpu_online_mask has been modified. > > So I suspect we need to change the state at which this is called > by CPU hotplug.
Yes the state idea is good, it's cleaner to have the CPU out of the online mask ahead of time.
I think we'll need two states. We want a CPU being offlined to already be removed from the online cpumask so and'ing the user-supplied and online masks reflects conditions after the hotplug operation is finished. For the same reason we want a CPU being onlined to already be in the online mask, and we can use the existing hotplug state for that, though we'd need a new padata-specific state for the offline case.
> IOW the commit that broke this is 30e92153b4e6.
I don't think 30e92153b4e6 is the one since the commit before that only allows __padata_remove_cpu to do its work if @cpu is in the online mask, so the call happens before cpu_online_mask has been modified. Same story for the very first padata commit, so it seems like that should actually be Fixes.
> This would also allow us to get rid of the two cpumask_clear_cpu > calls on pd->cpumask which is just bogus as you should only ever > modify the pd->cpumask prior to the padata_repalce call (because > the readers are not serialised with respect to this).
Yeah, makes sense.
Daniel
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