On 2019-10-22 02:41, Ming Lei wrote:
> On Mon, Oct 21, 2019 at 03:42:57PM -0700, Bart Van Assche wrote:
>> +int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
>> +{
>> + int ret;
>> +
>> + if (!percpu_ref_tryget(&q->q_usage_counter))
>> + return 0;
>> + ret = __blk_poll(q, cookie, spin);
>> + blk_queue_exit(q);
>> +
>> + return ret;
>> +}
>
> IMO, this change isn't required. Caller of blk_poll is supposed to
> hold refcount of the request queue, then the related hctx data structure
> won't go away. When the hctx is in transient state, there can't be IO
> to be polled, and it is safe to call into IO path.
>
> BTW, .poll is absolutely the fast path, we should be careful to add code
> in this path.
Hi Ming,
I'm not sure whether all blk_poll() callers really hold a refcount on
the request queue. Anyway, I will convert this code change into a
comment that explains that blk_poll() callers must hold a request queue
reference.
Bart.
