linux-kernel - Re: [PATCH v2 08/13] powerpc/hw_breakpoint: Avoid relying on caller synchronization

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Date:   Fri, 1 Jul 2022 10:15:17 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Marco Elver <elver@...gle.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v2 08/13] powerpc/hw_breakpoint: Avoid relying on caller
 synchronization



Le 01/07/2022 à 11:41, Marco Elver a écrit :
> On Fri, 1 Jul 2022 at 10:54, Christophe Leroy
> <christophe.leroy@...roup.eu> wrote:
>>
>> Hi Marco,
>>
>> Le 28/06/2022 à 11:58, Marco Elver a écrit :
>>> Internal data structures (cpu_bps, task_bps) of powerpc's hw_breakpoint
>>> implementation have relied on nr_bp_mutex serializing access to them.
>>>
>>> Before overhauling synchronization of kernel/events/hw_breakpoint.c,
>>> introduce 2 spinlocks to synchronize cpu_bps and task_bps respectively,
>>> thus avoiding reliance on callers synchronizing powerpc's hw_breakpoint.
>>
>> We have an still opened old issue in our database related to
>> hw_breakpoint, I was wondering if it could have any link with the
>> changes you are doing and whether you could handle it at the same time.
>>
>> https://github.com/linuxppc/issues/issues/38
>>
>> Maybe it is completely unrelated, but as your series modifies only
>> powerpc and as the issue says that powerpc is the only one to do that, I
>> thought it might be worth a hand up.
> 
> I see the powerpc issue unrelated to the optimizations in this series;
> perhaps by fixing the powerpc issue, it would also become more
> optimal. But all I saw is that it just so happens that powerpc relied
> on the nr_bp_mutex which is going away.
> 
> This series will become even more complex if I decided to add a
> powerpc rework on top (notwithstanding the fact I don't have any ppc
> hardware at my disposal either). A separate series/patch seems much
> more appropriate.
> 

Fair enough. Thanks for answering and clarifying.

Christophe