linux-kernel - Re: [PATCH][next] perf: arm-cmn: Fix unsigned comparison to less than zero

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Date:   Tue, 29 Sep 2020 18:17:01 +0100
From:   Will Deacon <will@...nel.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] perf: arm-cmn: Fix unsigned comparison to less
 than zero

On Tue, Sep 29, 2020 at 12:08:35PM -0500, Gustavo A. R. Silva wrote:
> Fix unsigned comparison to less than zero by assigning the returned
> value of function platform_get_irq() to a new integer variable _ret_
> and then make the comparison. In case the returned value is greater
> than or equal to zero, assign it to dtc->irq.
> 
> Addresses-Coverity-ID: 1497488 ("Unsigned compared against 0")
> Fixes: 0ba64770a2f2 ("perf: Add Arm CMN-600 PMU driver")
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/perf/arm-cmn.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index e824b5b83ea2..383b67042677 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -1246,11 +1246,13 @@ static int arm_cmn_init_dtc(struct arm_cmn *cmn, struct arm_cmn_node *dn, int id
>  {
>  	struct arm_cmn_dtc *dtc = cmn->dtc + idx;
>  	struct arm_cmn_node *xp;
> +	int ret;
>  
>  	dtc->base = dn->pmu_base - CMN_PMU_OFFSET;
> -	dtc->irq = platform_get_irq(to_platform_device(cmn->dev), idx);
> -	if (dtc->irq < 0)
> -		return dtc->irq;
> +	ret = platform_get_irq(to_platform_device(cmn->dev), idx);
> +	if (ret < 0)
> +		return ret;
> +	dtc->irq = ret;

Why don't we just change the type of the 'irq' field in 'struct arm_cmn_dtc'
to be 'int' instead of 'unsigned int'?

Robin?

Will