[PATCH] perf/arm-cmn: Fix invalid pointer when access dtc object sharing the same IRQ number

[Robin Murphy]

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 at arm.com>

> Fixes: 0ba64770a2f2 ("perf: Add Arm CMN-600 PMU driver")
> 
> Signed-off-by: Tuan Phan <tuanphan at 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;
>   			}
>   		}
>