[PATCH 2/2][SRU][xenial] blk-mq: Use proper cpumask iterator

[Christopher Arges]

On Mon, Aug 29, 2016 at 04:01:59PM -0400, Eric Desrochers wrote:
> From: Thomas Gleixner <tglx at linutronix.de>
> 
> BugLink: https://bugs.launchpad.net/bugs/1572630
> 
> queue_for_each_ctx() iterates over per_cpu variables under the assumption that
> the possible cpu mask cannot have holes. That's wrong as all cpumasks can have
> holes. In case there are holes the iteration ends up accessing uninitialized
> memory and crashing as a result.
> 
> Replace the macro by a proper for_each_possible_cpu() loop and drop the unused
> macro blk_ctx_sum() which references queue_for_each_ctx().
> 
> Reported-by: Xiong Zhou <jencce.kernel at gmail.com>
> Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
> Signed-off-by: Jens Axboe <axboe at fb.com>
> (cherry picked from commit 897bb0c7f1ea82d7cc882b19790b5e1df00ffc29)
> Signed-off-by: Eric Desrochers <eric.desrochers at canonical.com>
> ---
>  block/blk-mq-sysfs.c   |  5 ++++-
>  block/blk-mq.c         |  3 ++-
>  include/linux/blk-mq.h | 14 --------------
>  3 files changed, 6 insertions(+), 16 deletions(-)
> 
> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index 1cf1878..8d41163 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/block/blk-mq-sysfs.c
> @@ -413,14 +413,17 @@ static void blk_mq_sysfs_init(struct request_queue *q)
>  	struct blk_mq_hw_ctx *hctx;
>  	struct blk_mq_ctx *ctx;
>  	int i;
> +	int cpu;
> 

This is technically a 'backport' since it isn't a clean cherry-pick.
I see in the upstream patch that i was removed as we no longer have the
queue_for_each_hw_ctx loop.

--chris
>  	kobject_init(&q->mq_kobj, &blk_mq_ktype);
>  
>  	queue_for_each_hw_ctx(q, hctx, i)
>  		kobject_init(&hctx->kobj, &blk_mq_hw_ktype);
>  
> -	queue_for_each_ctx(q, ctx, i)
> +	for_each_possible_cpu(cpu) {
> +		ctx = per_cpu_ptr(q->queue_ctx, cpu);
>  		kobject_init(&ctx->kobj, &blk_mq_ctx_ktype);
> +	}
>  }
>  
>  int blk_mq_register_disk(struct gendisk *disk)
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 32598d2..92b7800 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1822,11 +1822,12 @@ static void blk_mq_map_swqueue(struct request_queue *q,
>  	/*
>  	 * Map software to hardware queues
>  	 */
> -	queue_for_each_ctx(q, ctx, i) {
> +	for_each_possible_cpu(i) {
>  		/* If the cpu isn't online, the cpu is mapped to first hctx */
>  		if (!cpumask_test_cpu(i, online_mask))
>  			continue;
>  
> +		ctx = per_cpu_ptr(q->queue_ctx, i);
>  		hctx = q->mq_ops->map_queue(q, i);
>  		cpumask_set_cpu(i, hctx->cpumask);
>  		ctx->index_hw = hctx->nr_ctx;
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 7fc9296..a8756cd 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -261,22 +261,8 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
>  	for ((i) = 0; (i) < (q)->nr_hw_queues &&			\
>  	     ({ hctx = (q)->queue_hw_ctx[i]; 1; }); (i)++)
>  
> -#define queue_for_each_ctx(q, ctx, i)					\
> -	for ((i) = 0; (i) < (q)->nr_queues &&				\
> -	     ({ ctx = per_cpu_ptr((q)->queue_ctx, (i)); 1; }); (i)++)
> -
>  #define hctx_for_each_ctx(hctx, ctx, i)					\
>  	for ((i) = 0; (i) < (hctx)->nr_ctx &&				\
>  	     ({ ctx = (hctx)->ctxs[(i)]; 1; }); (i)++)
>  
> -#define blk_ctx_sum(q, sum)						\
> -({									\
> -	struct blk_mq_ctx *__x;						\
> -	unsigned int __ret = 0, __i;					\
> -									\
> -	queue_for_each_ctx((q), __x, __i)				\
> -		__ret += sum;						\
> -	__ret;								\
> -})
> -
>  #endif
> -- 
> 2.7.4
> 
> 
> -- 
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team