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

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Date:   Mon, 07 May 2018 00:46:06 +0000
From:   Joel Fernandes <joel.opensrc@...il.com>
To:     frederic@...nel.org
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        jolsa@...hat.com, namhyung@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        torvalds@...ux-foundation.org, ysato@...rs.sourceforge.jp,
        benh@...nel.crashing.org,
        Catalin Marinas <catalin.marinas@....com>, chris@...kel.net,
        paulus@...ba.org, Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>, mpe@...erman.id.au,
        dalias@...c.org, Ingo Molnar <mingo@...nel.org>,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        luto@...nel.org, acme@...nel.org, jcmvbkbc@...il.com
Subject: Re: [PATCH 8/9] perf/breakpoint: Split breakpoint "check" and "commit"

On Sun, May 6, 2018 at 12:22 PM Frederic Weisbecker <frederic@...nel.org>
wrote:

> arch_validate_hwbkpt_settings() mixes up attribute check and commit into
> a single code entity. Therefore the validation may return an error due to
> incorrect atributes while still leaving halfway modified architecture
> breakpoint struct.

> Now that we have split its logic on all archs, we can remove this
> misdesigned function and call directly the arch check and commit
> functions instead. This allows us to later avoid commiting
> a breakpoint to architecture when its slot couldn't be allocated.

[...]
> 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);

minor nit:
To preserve bisectability, shouldn't this be the following in this and
earlier patches?

        err = hw_breakpoint_arch_check(bp, &bp->attr);
        hw_breakpoint_arch_commit(bp);
        if (err)
                return err;

And then in patch 9/9 you can fix it the right way?

thanks,

- Joel