On 10/12/22 11:43, Chao Leng wrote:
Add Ming Lei.
On 2022/10/12 14:37, Sagi Grimberg wrote:
On Sun, Jul 31, 2022 at 01:23:36PM +0300, Sagi Grimberg wrote:
But maybe we can avoid that, and because we allocate
the connect_q ourselves, and fully know that it should
not be apart of the tagset quiesce, perhaps we can introduce
a new interface like:
--
static inline int nvme_ctrl_init_connect_q(struct nvme_ctrl *ctrl)
{
ctrl->connect_q = blk_mq_init_queue_self_quiesce(ctrl->tagset);
if (IS_ERR(ctrl->connect_q))
return PTR_ERR(ctrl->connect_q);
return 0;
}
--
And then blk_mq_quiesce_tagset can simply look into a per
request-queue
self_quiesce flag and skip as needed.
I'd just make that a queue flag set after allocation to keep the
interface simple, but otherwise this seems like the right thing
to do.
Now the code used NVME_NS_STOPPED to avoid unpaired stop/start.
If we use blk_mq_quiesce_tagset, It will cause the above mechanism to
fail.
I review the code, only pci can not ensure secure stop/start pairing.
So there is a choice, We only use blk_mq_quiesce_tagset on fabrics,
not PCI.
Do you think that's acceptable?
If that's acceptable, I will try to send a patch set.
I don't think that this is acceptable. But I don't understand how
NVME_NS_STOPPED would change anything in the behavior of tagset-wide
quiesce?
If use blk_mq_quiesce_tagset, it will quiesce all queues of all ns,
but can not set NVME_NS_STOPPED of all ns. The mechanism of NVME_NS_STOPPED
will be invalidated.
NVMe-pci has very complicated quiesce/unquiesce use pattern,
quiesce/unquiesce
may be called unpaired.
It will cause some backward. There may be some bugs in this scenario:
A thread: quiesce the queue
B thread: quiesce the queue
A thread end, and does not unquiesce the queue.
B thread: unquiesce the queue, and do something which need the queue
must be unquiesed.
Of course, I don't think it is a good choice to guarantee paired access
through NVME_NS_STOPPED,
there exist unexpected unquiesce and start queue too early.
But now that the code has done so, the backward should be unacceptable.
such as this scenario:
A thread: quiesce the queue
B thread: want to quiesce the queue but do nothing because
NVME_NS_STOPPED is already set.
A thread: unquiesce the queue
Now the queue is unquiesced too early for B thread.
B thread: do something which need the queue must be quiesced.
Introduce NVME_NS_STOPPED link:
https://lore.kernel.org/all/20211014081710.1871747-5-ming.lei@xxxxxxxxxx/
I think we can just change a ns flag to a controller flag ala:
NVME_CTRL_STOPPED, and then do:
void nvme_stop_queues(struct nvme_ctrl *ctrl)
{
if (!test_and_set_bit(NVME_CTRL_STOPPED, &ns->flags))
blk_mq_quiesce_tagset(ctrl->tagset);
}
EXPORT_SYMBOL_GPL(nvme_stop_queues);
void nvme_start_queues(struct nvme_ctrl *ctrl)
{
if (test_and_clear_bit(NVME_CTRL_STOPPED, &ns->flags))
blk_mq_unquiesce_tagset(ctrl->tagset);
}
EXPORT_SYMBOL_GPL(nvme_start_queues);
Won't that achieve the same result?
