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SubjectRe: [PATCH] nvme-core: Fix subsystem instance mismatches
On Wed, Sep 04, 2019 at 10:07:12AM -0600, Logan Gunthorpe wrote:
> Yes, I agree, we can't solve the mismatch problem in the general case:
> with sequences of hot plug events there will always be a case that
> mismatches. I just think we can do better in the simple common default case.

This may be something where udev can help us. I might be able to find
some time to look at that, but not today.

> > Can we just ensure there is never a matching controller then? This
> > patch will accomplish that and simpler than wrapping the instance in a
> > refcount'ed object:
> >
> > http://lists.infradead.org/pipermail/linux-nvme/2019-May/024142.html
>
> I don't really like that idea. It reduces the confusion caused by
> mismatching numbers, but causes the controller to never match the
> namespace, which is also confusing but in a different way.
>
> I like the nvme_instance idea. It's not going to be perfect but it has
> some nice properties: the subsystem will try to match the controller's
> instance whenever possible, but in cases where it doesn't, the instance
> number of the subsystem will never be the same as an existing controller.
>
> I'll see if I can work up a quick patch set and see what people think.

How about this: we have the subsys copy the controller's instance,
and the nvme_free_ctrl() doesn't release it if its subsys matches?

---
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 14c0bfb55615..8a8279ece5ee 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -81,7 +81,6 @@ EXPORT_SYMBOL_GPL(nvme_reset_wq);
struct workqueue_struct *nvme_delete_wq;
EXPORT_SYMBOL_GPL(nvme_delete_wq);

-static DEFINE_IDA(nvme_subsystems_ida);
static LIST_HEAD(nvme_subsystems);
static DEFINE_MUTEX(nvme_subsystems_lock);

@@ -2344,7 +2343,8 @@ static void nvme_release_subsystem(struct device *dev)
struct nvme_subsystem *subsys =
container_of(dev, struct nvme_subsystem, dev);

- ida_simple_remove(&nvme_subsystems_ida, subsys->instance);
+ if (subsys->instance >= 0)
+ ida_simple_remove(&nvme_instance_ida, subsys->instance);
kfree(subsys);
}

@@ -2473,12 +2473,8 @@ static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
subsys = kzalloc(sizeof(*subsys), GFP_KERNEL);
if (!subsys)
return -ENOMEM;
- ret = ida_simple_get(&nvme_subsystems_ida, 0, 0, GFP_KERNEL);
- if (ret < 0) {
- kfree(subsys);
- return ret;
- }
- subsys->instance = ret;
+
+ subsys->instance = -1;
mutex_init(&subsys->lock);
kref_init(&subsys->ref);
INIT_LIST_HEAD(&subsys->ctrls);
@@ -2497,7 +2493,7 @@ static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
subsys->dev.class = nvme_subsys_class;
subsys->dev.release = nvme_release_subsystem;
subsys->dev.groups = nvme_subsys_attrs_groups;
- dev_set_name(&subsys->dev, "nvme-subsys%d", subsys->instance);
+ dev_set_name(&subsys->dev, "nvme-subsys%d", ctrl->instance);
device_initialize(&subsys->dev);

mutex_lock(&nvme_subsystems_lock);
@@ -2528,6 +2524,8 @@ static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
goto out_put_subsystem;
}

+ if (!found)
+ subsys->instance = ctrl->instance;
ctrl->subsys = subsys;
list_add_tail(&ctrl->subsys_entry, &subsys->ctrls);
mutex_unlock(&nvme_subsystems_lock);
@@ -3803,7 +3801,9 @@ static void nvme_free_ctrl(struct device *dev)
container_of(dev, struct nvme_ctrl, ctrl_device);
struct nvme_subsystem *subsys = ctrl->subsys;

- ida_simple_remove(&nvme_instance_ida, ctrl->instance);
+ if (subsys && ctrl->instance != subsys->instance)
+ ida_simple_remove(&nvme_instance_ida, ctrl->instance);
+
kfree(ctrl->effects);
nvme_mpath_uninit(ctrl);
__free_page(ctrl->discard_page);
@@ -4085,7 +4085,6 @@ static int __init nvme_core_init(void)

static void __exit nvme_core_exit(void)
{
- ida_destroy(&nvme_subsystems_ida);
class_destroy(nvme_subsys_class);
class_destroy(nvme_class);
unregister_chrdev_region(nvme_chr_devt, NVME_MINORS);
--
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