Re: [stable-4.4 1/5] padata: set cpu_index of unused CPUs to -1

[Ben Hutchings <ben@decadent.org.uk>]

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On Thu, 2020-05-21 at 16:51 -0400, Daniel Jordan wrote:
> From: Mathias Krause <minipli@googlemail.com>
> 
> [ Upstream commit 1bd845bcb41d5b7f83745e0cb99273eb376f2ec5 ]

Well spotted, I'll add this for 3.16 as well.

Ben.

> The parallel queue per-cpu data structure gets initialized only for CPUs
> in the 'pcpu' CPU mask set. This is not sufficient as the reorder timer
> may run on a different CPU and might wrongly decide it's the target CPU
> for the next reorder item as per-cpu memory gets memset(0) and we might
> be waiting for the first CPU in cpumask.pcpu, i.e. cpu_index 0.
> 
> Make the '__this_cpu_read(pd->pqueue->cpu_index) == next_queue->cpu_index'
> compare in padata_get_next() fail in this case by initializing the
> cpu_index member of all per-cpu parallel queues. Use -1 for unused ones.
> 
> Signed-off-by: Mathias Krause <minipli@googlemail.com>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
> ---
>  kernel/padata.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 8aef48c3267b..4f860043a8e5 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -461,8 +461,14 @@ static void padata_init_pqueues(struct parallel_data *pd)
>  	struct padata_parallel_queue *pqueue;
>  
>  	cpu_index = 0;
> -	for_each_cpu(cpu, pd->cpumask.pcpu) {
> +	for_each_possible_cpu(cpu) {
>  		pqueue = per_cpu_ptr(pd->pqueue, cpu);
> +
> +		if (!cpumask_test_cpu(cpu, pd->cpumask.pcpu)) {
> +			pqueue->cpu_index = -1;
> +			continue;
> +		}
> +
>  		pqueue->pd = pd;
>  		pqueue->cpu_index = cpu_index;
>  		cpu_index++;
-- 
Ben Hutchings
Logic doesn't apply to the real world. - Marvin Minsky



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