Re: [PATCH] blk-mq: don't leak preempt counter/q_usage_counter when allocating rq failed

On 07/14/2017 02:41 AM, Ming Lei wrote:

From: Ming Lei <redacted>

When blk_mq_get_request() failed, preempt counter isn't
released, and blk_mq_make_request() doesn't release the counter
too.

This patch fixes the issue, and makes sure that preempt counter
is only held if rq is allocated successfully. The same policy is
applied on .q_usage_counter too.

Can you replace the 'get_cpu' bool with just a ctx, and change
the logic to put it if set? I think that would be cleaner to read,
generally I hate bool 'do_something' variables that are set. It's
much cleaner to have:

if (likely(!data->ctx))
	data->ctx = local_ctx = blk_mq_get_ctx(q);

and have the put case be

if (local_ctx)
	blk_mq_put_ctx(local_ctx);

Either that, or at least just have blk_mq_get_request() do:

drop_ctx = data->ctx == NULL;

instead. The 'get_cpu' naming is confusing, we're worried about dropping
the sw queue here, the fact that it's related to get/put_cpu() need not
bubble up here.

-- 
Jens Axboe