linux-kernel - Re: [PATCH 8/9] perf/breakpoint: Split breakpoint "check" and "commit"

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Date:   Tue, 15 May 2018 15:58:57 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Chris Zankel <chris@...kel.net>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Rich Felker <dalias@...c.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Max Filippov <jcmvbkbc@...il.com>
Subject: Re: [PATCH 8/9] perf/breakpoint: Split breakpoint "check" and
 "commit"

On Tue, May 15, 2018 at 08:57:47AM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Sun, May 06, 2018 at 09:19:54PM +0200, Frederic Weisbecker wrote:
> > >  arch/arm/include/asm/hw_breakpoint.h     |  5 ++++-
> > >  arch/arm/kernel/hw_breakpoint.c          | 22 +++-------------------
> > >  arch/arm64/include/asm/hw_breakpoint.h   |  5 ++++-
> > >  arch/arm64/kernel/hw_breakpoint.c        | 22 +++-------------------
> > >  arch/powerpc/include/asm/hw_breakpoint.h |  5 ++++-
> > >  arch/powerpc/kernel/hw_breakpoint.c      | 22 +++-------------------
> > >  arch/sh/include/asm/hw_breakpoint.h      |  5 ++++-
> > >  arch/sh/kernel/hw_breakpoint.c           | 22 +++-------------------
> > >  arch/x86/include/asm/hw_breakpoint.h     |  5 ++++-
> > >  arch/x86/kernel/hw_breakpoint.c          | 23 +++--------------------
> > >  arch/xtensa/include/asm/hw_breakpoint.h  |  5 ++++-
> > >  arch/xtensa/kernel/hw_breakpoint.c       | 22 +++-------------------
> > 
> > Because of those ^,
> > 
> > >  kernel/events/hw_breakpoint.c            | 11 ++++++-----
> > 
> > would it not make sense to have a prelimenary patch doing something
> > like:
> > 
> > __weak int hw_breakpoint_arch_check(struct perf_event *bp)
> > {
> > 	return arch_validate_hwbkpt_settings(bp);
> > }
> > 
> > __weak void hw_breakpoint_arch_commit(struct perf_event *bp)
> > {
> > }
> > 
> > combined with this bit:
> > 
> > > diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> > > index 6e28d28..6896ceeb 100644
> > > --- a/kernel/events/hw_breakpoint.c
> > > +++ b/kernel/events/hw_breakpoint.c
> > > @@ -402,11 +402,12 @@ int dbg_release_bp_slot(struct perf_event *bp)
> > >  
> > >  static int validate_hw_breakpoint(struct perf_event *bp)
> > >  {
> > > -	int ret;
> > > +	int err;
> > >  
> > > -	ret = arch_validate_hwbkpt_settings(bp);
> > > -	if (ret)
> > > -		return ret;
> > > +	err = hw_breakpoint_arch_check(bp, &bp->attr);
> > > +	if (err)
> > > +		return err;
> > > +	hw_breakpoint_arch_commit(bp);
> > >  
> > >  	if (arch_check_bp_in_kernelspace(bp)) {
> > >  		if (bp->attr.exclude_kernel)
> > 
> > And then convert the archs over one by one, and at the end remove the
> > weak thingies entirely?
> 
> Makes sense.
> 
> The rest looks good to me - Frederic, once you implement Peter's uggestion I 
> suspect this series can be applied.

Right, I'll try to do a smoother transition as in Peterz suggestion.
I'm just going to pass around the struct arch_hw_breakpoint to avoid code
duplication in check and commit. The end result may look like:

    struct arch_hw_breakpoint hw;
    int err;

    err = hw_breakpoint_arch_parse(bp, attr, &hw);
    if (err)
        return err;

    .....

    bp->hw.info = hw;