linux-kernel - Re: [PATCH] perf: arm_spe: handle devm

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Message-ID: <20181129121432.2ntsfhp2s43gyvfx@lakrids.cambridge.arm.com>
Date:   Thu, 29 Nov 2018 12:14:32 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Nicholas Mc Guire <hofrat@...dl.org>
Cc:     Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: arm_spe: handle devm_kasprintf() failure

On Wed, Nov 28, 2018 at 12:24:47PM +0100, Nicholas Mc Guire wrote:
> devm_kasprintf() may return NULL on failure of internal allocation
> thus the assignment to  name  is not safe if unchecked. if NULL
> is passed in for name then perf_pmu_register() would not fail
> but rather silently jump to skip_type which is not the intent
> here. As perf_pmu_register() may also return -ENOMEM returning 
> -ENOMEM in the (unlikely) failure case of devm_kasprintf() should 
> be fine here as well.
> 
> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> Fixes: d5d9696b0380 ("drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension")
> ---
> 
> Problem located with an experimental coccinelle script
> 
> The dev_err() might seem a bit much for this unlikely error but as 
> perf_pmu_register() may also return -ENOMEM it would be hard to figure
> out what went wrong without this message.
> 
> Patch was compile tested with: defconfig (ARCH=arm64) +
> ARM_SPE_PMU=y
> 
> Patch is against 4.20-rc3 (localversion-next is next-20181128)
> 
>  drivers/perf/arm_spe_pmu.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
> index 54ec278..f1ea00c 100644
> --- a/drivers/perf/arm_spe_pmu.c
> +++ b/drivers/perf/arm_spe_pmu.c
> @@ -927,6 +927,11 @@ static int arm_spe_pmu_perf_init(struct arm_spe_pmu *spe_pmu)
>  
>  	idx = atomic_inc_return(&pmu_idx);
>  	name = devm_kasprintf(dev, GFP_KERNEL, "%s_%d", PMUNAME, idx);
> +	if (!name) {
> +		dev_err(dev, "Allocation of name failed\n");
> +		return -ENOMEM;
> +	}

In the other dev_err() messages, we use the form "failed to ...", e.g.

	"failed to get IRQ (%d)\n"
	"failed to get PPI partition (%d)\n
	"failed to allocate spe_pmu\n"

... so for consistency could you please change the string to:

	"failed to allocate spe_pmu name\n"

With that, feel free to add:

Acked-by: Mark Rutland <mark.rutland@....com>

Mark.