Re: [PATCH] MIPS: smp.c: Fix uninitialised temp_foreign_map

[Matt Redfearn <matt.redfearn@imgtec.com>]

Hi James,

On 04/03/16 10:10, James Hogan wrote:
> When calculate_cpu_foreign_map() recalculates the cpu_foreign_map
> cpumask it uses the local variable temp_foreign_map without initialising
> it to zero. Since the calculation only ever sets bits in this cpumask
> any existing bits at that memory location will remain set and find their
> way into cpu_foreign_map too. This could potentially lead to cache
> operations suboptimally doing smp calls to multiple VPEs in the same
> core, even though the VPEs share primary caches.
>
> Therefore initialise temp_foreign_map using cpumask_clear() before use.
>
> Fixes: cccf34e9411c ("MIPS: c-r4k: Fix cache flushing for MT cores")

cccf34e9411c was CC'd to stable 3.15+, should this fix do the same?

Thanks,
Matt


> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: Paul Burton <paul.burton@imgtec.com>
> Cc: linux-mips@linux-mips.org
> ---
>   arch/mips/kernel/smp.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
> index bd4385a8e6e8..2b521e07b860 100644
> --- a/arch/mips/kernel/smp.c
> +++ b/arch/mips/kernel/smp.c
> @@ -121,6 +121,7 @@ static inline void calculate_cpu_foreign_map(void)
>   	cpumask_t temp_foreign_map;
>   
>   	/* Re-calculate the mask */
> +	cpumask_clear(&temp_foreign_map);
>   	for_each_online_cpu(i) {
>   		core_present = 0;
>   		for_each_cpu(k, &temp_foreign_map)