[PATCH 1/8] blk-mq: add blk_mq_alloc_request_hctx

[Ming Lin]

On Tue, Jun 7, 2016 at 8:27 AM, Ming Lin <mlin at kernel.org> wrote:
> On Tue, Jun 7, 2016 at 7:57 AM, Keith Busch <keith.busch at intel.com> wrote:
>> On Mon, Jun 06, 2016 at 11:21:52PM +0200, Christoph Hellwig wrote:
>>> +struct request *blk_mq_alloc_request_hctx(struct request_queue *q, int rw,
>>> +             unsigned int flags, unsigned int hctx_idx)
>>> +{
>>> +     struct blk_mq_hw_ctx *hctx;
>>> +     struct blk_mq_ctx *ctx;
>>> +     struct request *rq;
>>> +     struct blk_mq_alloc_data alloc_data;
>>> +     int ret;
>>> +
>>> +     ret = blk_queue_enter(q, flags & BLK_MQ_REQ_NOWAIT);
>>> +     if (ret)
>>> +             return ERR_PTR(ret);
>>> +
>>> +     hctx = q->queue_hw_ctx[hctx_idx];
>>
>> We probably want to check 'if (hctx_idx < q->nr_hw_queues)' before
>> getting the hctx. Even if hctx_idx was origially valid, it's possible
>> (though unlikely) blk_queue_enter waits on reallocating h/w contexts,
>> which can make hctx_idx invalid.
>
> Yes, I'll update it.

How about this?

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7bb45ed..b59d2ef 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -279,6 +279,11 @@ struct request *blk_mq_alloc_request_hctx(struct
request_queue *q, int rw,
        if (ret)
                return ERR_PTR(ret);

+       if (hctx_idx >= q->nr_hw_queues) {
+               blk_queue_exit(q);
+               return ERR_PTR(-EINVAL);
+       }
+
        hctx = q->queue_hw_ctx[hctx_idx];
        ctx = __blk_mq_get_ctx(q, cpumask_first(hctx->cpumask));