linux-kernel - Re: [PATCH resent] perf/x86/amd/uncore: Fix exception handling in amd_uncore_cpu_up

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Date:   Mon, 27 Mar 2023 12:11:54 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Markus Elfring <Markus.Elfring@....de>,
        kernel-janitors@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ian Rogers <irogers@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sandipan Das <sandipan.das@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Zhouyi Zhou <zhouzhouyi@...il.com>, x86@...nel.org
Cc:     cocci@...ia.fr, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH resent] perf/x86/amd/uncore: Fix exception handling in
 amd_uncore_cpu_up_prepare()

On 25/03/23 16:15, Markus Elfring wrote:
> Date: Fri, 17 Mar 2023 13:13:14 +0100
> 
> The label “fail” was used to jump to another pointer check despite of
> the detail in the implementation of the function “amd_uncore_cpu_up_prepare”
> that it was determined already that the corresponding variable contained
> a null pointer (because of a failed function call in two cases).
> 
> 1. Thus return directly after a call of the function “amd_uncore_alloc”
>    failed in the first if branch.
> 
> 2. Use more appropriate labels instead.
> 
> 3. Reorder jump targets at the end.
> 
> 4. Delete a redundant check and kfree() call.
> 
> 5. Omit an explicit initialisation for the local variable “uncore_llc”.
> 
> 
> This issue was detected by using the Coccinelle software.
> 
> Fixes: 39621c5808f5dda75d03dc4b2d4d2b13a5a1c34b ("perf/x86/amd/uncore: Use dynamic events array")
> Fixes: 503d3291a937b726757c1f7c45fa02389d2f4324 ("perf/x86/amd: Try to fix some mem allocation failure handling")

Commit should be only the first 12 characters of the hash.
Refer:	https://docs.kernel.org/process/submitting-patches.html

But this is not a fix. Redundant calls to kfree do not break
anything.

Also avoid using the term "exception" since, in x86, exceptions are
hardware events.  Better to just call it "error handling".

> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  arch/x86/events/amd/uncore.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
> index 83f15fe411b3..0a9b5cb97bb4 100644
> --- a/arch/x86/events/amd/uncore.c
> +++ b/arch/x86/events/amd/uncore.c
> @@ -440,13 +440,13 @@ amd_uncore_events_alloc(unsigned int num, unsigned int cpu)
> 
>  static int amd_uncore_cpu_up_prepare(unsigned int cpu)
>  {
> -	struct amd_uncore *uncore_nb = NULL, *uncore_llc = NULL;
> +	struct amd_uncore *uncore_nb = NULL, *uncore_llc;
> 
>  	if (amd_uncore_nb) {
>  		*per_cpu_ptr(amd_uncore_nb, cpu) = NULL;
>  		uncore_nb = amd_uncore_alloc(cpu);
>  		if (!uncore_nb)
> -			goto fail;
> +			return -ENOMEM;
>  		uncore_nb->cpu = cpu;
>  		uncore_nb->num_counters = num_counters_nb;
>  		uncore_nb->rdpmc_base = RDPMC_BASE_NB;
> @@ -455,7 +455,7 @@ static int amd_uncore_cpu_up_prepare(unsigned int cpu)
>  		uncore_nb->pmu = &amd_nb_pmu;
>  		uncore_nb->events = amd_uncore_events_alloc(num_counters_nb, cpu);
>  		if (!uncore_nb->events)
> -			goto fail;
> +			goto free_nb;
>  		uncore_nb->id = -1;
>  		*per_cpu_ptr(amd_uncore_nb, cpu) = uncore_nb;
>  	}
> @@ -464,7 +464,7 @@ static int amd_uncore_cpu_up_prepare(unsigned int cpu)
>  		*per_cpu_ptr(amd_uncore_llc, cpu) = NULL;
>  		uncore_llc = amd_uncore_alloc(cpu);
>  		if (!uncore_llc)
> -			goto fail;
> +			goto check_uncore_nb;
>  		uncore_llc->cpu = cpu;
>  		uncore_llc->num_counters = num_counters_llc;
>  		uncore_llc->rdpmc_base = RDPMC_BASE_LLC;
> @@ -473,24 +473,22 @@ static int amd_uncore_cpu_up_prepare(unsigned int cpu)
>  		uncore_llc->pmu = &amd_llc_pmu;
>  		uncore_llc->events = amd_uncore_events_alloc(num_counters_llc, cpu);
>  		if (!uncore_llc->events)
> -			goto fail;
> +			goto free_llc;
>  		uncore_llc->id = -1;
>  		*per_cpu_ptr(amd_uncore_llc, cpu) = uncore_llc;
>  	}
> 
>  	return 0;
> 
> -fail:
> +free_llc:
> +	kfree(uncore_llc);
> +check_uncore_nb:
>  	if (uncore_nb) {
>  		kfree(uncore_nb->events);
> +free_nb:
>  		kfree(uncore_nb);
>  	}
> 
> -	if (uncore_llc) {
> -		kfree(uncore_llc->events);
> -		kfree(uncore_llc);
> -	}
> -
>  	return -ENOMEM;
>  }
> 
> --
> 2.40.0
>