linux-kernel - Re: [PATCH] powerpc/perf: Use guard(irqsave)() in eight functions

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Message-ID: <871q1eoqya.fsf@mail.lhotse>
Date: Fri, 20 Sep 2024 15:05:17 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Markus Elfring <Markus.Elfring@....de>, linuxppc-dev@...ts.ozlabs.org,
 Anjali K <anjalik@...ux.ibm.com>, Christophe Leroy
 <christophe.leroy@...roup.eu>, Kan Liang <kan.liang@...ux.intel.com>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>, Naveen N Rao
 <naveen@...nel.org>, Nicholas Piggin <npiggin@...il.com>, Peter Zijlstra
 <peterz@...radead.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Julia Lawall <julia.lawall@...ia.fr>
Subject: Re: [PATCH] powerpc/perf: Use guard(irqsave)() in eight functions

Markus Elfring <Markus.Elfring@....de> writes:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Mon, 16 Sep 2024 19:25:00 +0200
>
> Scope-based resource management became supported for some
> programming interfaces by contributions of Peter Zijlstra on 2023-05-26.
> See also the commit 54da6a0924311c7cf5015533991e44fb8eb12773 ("locking:
> Introduce __cleanup() based infrastructure").
>
> * Thus replace local_irq_save() and local_irq_restore() calls by calls
>   of the macro “guard(irqsave)”.
>
> * Omit the local variables “flags” and “irq_flags”.
>
> * Replace selected usage of the label “out” by a few return statements.
>
>
> This issue was detected by using the Coccinelle software.
>
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  arch/powerpc/perf/core-book3s.c | 102 +++++++++++++-------------------
>  1 file changed, 42 insertions(+), 60 deletions(-)

These mostly look good.

I don't think the change to power_pmu_event_init() is an improvement.

I'll drop that hunk when applying, or you can send a v2 without that
change if you prefer.

cheers

> @@ -1996,7 +1980,7 @@ static bool is_event_blacklisted(u64 ev)
>  static int power_pmu_event_init(struct perf_event *event)
>  {
>  	u64 ev;
> -	unsigned long flags, irq_flags;
> +	unsigned long flags;
>  	struct perf_event *ctrs[MAX_HWEVENTS];
>  	u64 events[MAX_HWEVENTS];
>  	unsigned int cflags[MAX_HWEVENTS];
> @@ -2115,43 +2099,41 @@ static int power_pmu_event_init(struct perf_event *event)
>  	if (check_excludes(ctrs, cflags, n, 1))
>  		return -EINVAL;
>
> -	local_irq_save(irq_flags);
> -	cpuhw = this_cpu_ptr(&cpu_hw_events);
> +	{
> +		guard(irqsave)();
> +		cpuhw = this_cpu_ptr(&cpu_hw_events);
>
> -	err = power_check_constraints(cpuhw, events, cflags, n + 1, ctrs);
> +		err = power_check_constraints(cpuhw, events, cflags, n + 1, ctrs);
>
> -	if (has_branch_stack(event)) {
> -		u64 bhrb_filter = -1;
> +		if (has_branch_stack(event)) {
> +			u64 bhrb_filter = -1;
>
> -		/*
> -		 * Currently no PMU supports having multiple branch filters
> -		 * at the same time. Branch filters are set via MMCRA IFM[32:33]
> -		 * bits for Power8 and above. Return EOPNOTSUPP when multiple
> -		 * branch filters are requested in the event attr.
> -		 *
> -		 * When opening event via perf_event_open(), branch_sample_type
> -		 * gets adjusted in perf_copy_attr(). Kernel will automatically
> -		 * adjust the branch_sample_type based on the event modifier
> -		 * settings to include PERF_SAMPLE_BRANCH_PLM_ALL. Hence drop
> -		 * the check for PERF_SAMPLE_BRANCH_PLM_ALL.
> -		 */
> -		if (hweight64(event->attr.branch_sample_type & ~PERF_SAMPLE_BRANCH_PLM_ALL) > 1) {
> -			local_irq_restore(irq_flags);
> -			return -EOPNOTSUPP;
> -		}
> +			/*
> +			 * Currently no PMU supports having multiple branch filters
> +			 * at the same time. Branch filters are set via MMCRA IFM[32:33]
> +			 * bits for Power8 and above. Return EOPNOTSUPP when multiple
> +			 * branch filters are requested in the event attr.
> +			 *
> +			 * When opening event via perf_event_open(), branch_sample_type
> +			 * gets adjusted in perf_copy_attr(). Kernel will automatically
> +			 * adjust the branch_sample_type based on the event modifier
> +			 * settings to include PERF_SAMPLE_BRANCH_PLM_ALL. Hence drop
> +			 * the check for PERF_SAMPLE_BRANCH_PLM_ALL.
> +			 */
> +			if (hweight64(event->attr.branch_sample_type & ~PERF_SAMPLE_BRANCH_PLM_ALL)
> +			    > 1)
> +				return -EOPNOTSUPP;
>
> -		if (ppmu->bhrb_filter_map)
> -			bhrb_filter = ppmu->bhrb_filter_map(
> -					event->attr.branch_sample_type);
> +			if (ppmu->bhrb_filter_map)
> +				bhrb_filter = ppmu->bhrb_filter_map(event->attr.branch_sample_type);
>
> -		if (bhrb_filter == -1) {
> -			local_irq_restore(irq_flags);
> -			return -EOPNOTSUPP;
> +			if (bhrb_filter == -1)
> +				return -EOPNOTSUPP;
> +
> +			cpuhw->bhrb_filter = bhrb_filter;
>  		}
> -		cpuhw->bhrb_filter = bhrb_filter;
>  	}
>
> -	local_irq_restore(irq_flags);
>  	if (err)
>  		return -EINVAL;
>
> --
> 2.46.0