On 2022/10/13 9:37, Chao Leng wrote:
On 2022/10/12 19:13, Sagi Grimberg wrote:
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?
No, nvme_set_queue_dying call nvme_start_ns_queue for one ns.
ctrl->flags can not cover this scenario.
This still results in unpaired quiesce/unquiesce.
Maybe it is necessary to clean up the confused quiesce/unquiesce of nvme-pci,
Thus blk_mq_quiesce_tagset can be easy to use for nvme-pci.
Before that, we could only optimize batched quiesce/unquiesce based on ns,
Although I also think using blk_mq_quiesce_tagset is a better choice.
We can do some something special for nvme_set_queue_dying.
Thus can achieve the same effect with NVME_NS_STOPPED.
This should look acceptable.
What do you think about this?
Show the code:
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -5100,13 +5100,14 @@ static void nvme_stop_ns_queue(struct nvme_ns *ns)
* holding bd_butex. This will end buffered writers dirtying pages that can't
* be synced.
*/
-static void nvme_set_queue_dying(struct nvme_ns *ns)
+static void nvme_set_queue_dying(struct nvme_ns *ns, bool start_queue)
{
if (test_and_set_bit(NVME_NS_DEAD, &ns->flags))
return;
blk_mark_disk_dead(ns->disk);
- nvme_start_ns_queue(ns);
+ if (start_queue)
+ blk_mq_unquiesce_queue(ns->queue);
set_capacity_and_notify(ns->disk, 0);
}
@@ -5121,15 +5122,18 @@ static void nvme_set_queue_dying(struct nvme_ns *ns)
void nvme_kill_queues(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;
+ bool start_queue = false;
down_read(&ctrl->namespaces_rwsem);
/* Forcibly unquiesce queues to avoid blocking dispatch */
if (ctrl->admin_q && !blk_queue_dying(ctrl->admin_q))
nvme_start_admin_queue(ctrl);
+ if (test_and_clear_bit(NVME_CTRL_STOPPED, &ctrl->flags))
+ start_queue = true;
list_for_each_entry(ns, &ctrl->namespaces, list)
- nvme_set_queue_dying(ns);
+ nvme_set_queue_dying(ns, start_queue);
up_read(&ctrl->namespaces_rwsem);
}
.
