linux-kernel - Re: [RFC][PATCH 2/2] sched: Use fancy new guards

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d806769b-c568-fa7c-f7aa-ded9ffea11b4@efficios.com>
Date:   Fri, 26 May 2023 12:27:51 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, keescook@...omium.org,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        ojeda@...nel.org, ndesaulniers@...gle.com, mingo@...hat.com,
        will@...nel.org, longman@...hat.com, boqun.feng@...il.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        paulmck@...nel.org, frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, josh@...htriplett.org,
        jiangshanlai@...il.com, qiang1.zhang@...el.com,
        rcu@...r.kernel.org, tj@...nel.org, tglx@...utronix.de
Subject: Re: [RFC][PATCH 2/2] sched: Use fancy new guards

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@...radead.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