I suggest to drop sync_r4k completely, because it is inaccurate. You
can use IPI to synchronize count/compare instead, as Loongson-3 does.
Huacai
On Mon, Aug 28, 2017 at 6:07 PM, Matija Glavinic Pecotic
<matija.glavinic-pecotic....@nokia.com> wrote:
> On 08/23/2017 10:21 AM, Matt Redfearn wrote:
>> As noted in the commit message, upstream differs in this area. The
>> hotplug code now waits on a completion event in bringup_wait_for_ap,
>> which is set by the starting CPU in cpuhp_online_idle once it calls
>> cpu_startup_entry. Thus there is no possibility of a race in upstream,
>> and this commit has only re-introduced the deadlock condition, which can
>> be observed on multiple platforms when running a heavy load test at the
>> same time as hotplugging CPUs. See commit 8f46cca1e6c06 ("MIPS: SMP: Fix
>> possibility of deadlock when bringing CPUs online") for details.
>
> I personally do not like the fact that synchronization is implicitly done by
> the callers, it is the reason why the patch was proposed. As noted before, it
> is enough someone checks cpu online mask somewhere in between and there is
> race again.
>
> How about moving synchronise_count_slave before setting the cpu online? Is
> there dependency it has to be done after completion?
>
> Regards,
>
> Matija
>
