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SubjectRe: [RFC][PATCH 2/2] sched: Use fancy new guards
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On 5/26/23 12:25, Greg KH wrote:
> On Fri, May 26, 2023 at 05:05:51PM +0200, Peter Zijlstra wrote:
>> Convert kernel/sched/core.c to use the fancy new guards to simplify
>> the error paths.
>
> That's slightly crazy...
>
> I like the idea, but is this really correct:
>
>
>>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>> ---
>> kernel/sched/core.c | 1223 +++++++++++++++++++++++----------------------------
>> kernel/sched/sched.h | 39 +
>> 2 files changed, 595 insertions(+), 667 deletions(-)
>>
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -1097,24 +1097,21 @@ int get_nohz_timer_target(void)
>>
>> hk_mask = housekeeping_cpumask(HK_TYPE_TIMER);
>>
>> - rcu_read_lock();
>> - for_each_domain(cpu, sd) {
>> - for_each_cpu_and(i, sched_domain_span(sd), hk_mask) {
>> - if (cpu == i)
>> - continue;
>> + void_scope(rcu) {
>> + for_each_domain(cpu, sd) {
>> + for_each_cpu_and(i, sched_domain_span(sd), hk_mask) {
>> + if (cpu == i)
>> + continue;
>>
>> - if (!idle_cpu(i)) {
>> - cpu = i;
>> - goto unlock;
>> + if (!idle_cpu(i))
>> + return i;
>
> You can call return from within a "scope" and it will clean up properly?
>
> I tried to read the cpp "mess" but couldn't figure out how to validate
> this at all, have a set of tests for this somewhere?
>
> Anyway, the naming is whack, but I don't have a proposed better name,
> except you might want to put "scope_" as the prefix not the suffix, but
> then that might look odd to, so who knows.

FWIW C++ has std::scoped_lock. So perhaps using a similar wording may help ?

Thanks,

Mathieu

>
> But again, the idea is good, it might save us lots of "you forgot to
> clean this up on the error path" mess that we are getting constant churn
> for these days...
>
> thanks,
>
> greg k-h

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

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