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Subject: Re: [PATCH] perf/arm-cmn: Fix invalid pointer when access dtc object
 sharing the same IRQ number
To:     Tuan Phan <tuanphan@os.amperecomputing.com>
Cc:     Will Deacon <will@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <1623946129-3290-1-git-send-email-tuanphan@os.amperecomputing.com>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <b3f1126d-2906-cf36-4d3d-eb86552fa50b@arm.com>
Date:   Thu, 17 Jun 2021 18:48:06 +0100
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On 2021-06-17 17:08, Tuan Phan wrote:
> When multiple dtcs share the same IRQ number, the irq_friend which
> used to refer to dtc object gets calculated incorrect which leads
> to invalid pointer.

Oops, indeed this is supposed to be a forward offset *from* the previous 
match *to* the current dtc. It's almost as if I never managed to test 
it... :)

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Fixes: 0ba64770a2f2 ("perf: Add Arm CMN-600 PMU driver")
> 
> Signed-off-by: Tuan Phan <tuanphan@os.amperecomputing.com>
> ---
>   drivers/perf/arm-cmn.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index 56a5c35..49016f2 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -1212,7 +1212,7 @@ static int arm_cmn_init_irqs(struct arm_cmn *cmn)
>   		irq = cmn->dtc[i].irq;
>   		for (j = i; j--; ) {
>   			if (cmn->dtc[j].irq == irq) {
> -				cmn->dtc[j].irq_friend = j - i;
> +				cmn->dtc[j].irq_friend = i - j;
>   				goto next;
>   			}
>   		}
>