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Re: [PATCH v2 4/4] hw/nvme: fix controller hot unplugging


From: Klaus Jensen
Subject: Re: [PATCH v2 4/4] hw/nvme: fix controller hot unplugging
Date: Wed, 7 Jul 2021 18:56:31 +0200

On Jul  7 17:57, Hannes Reinecke wrote:
On 7/7/21 5:49 PM, Klaus Jensen wrote:
From: Klaus Jensen <k.jensen@samsung.com>

Prior to this patch the nvme-ns devices are always children of the
NvmeBus owned by the NvmeCtrl. This causes the namespaces to be
unrealized when the parent device is removed. However, when subsystems
are involved, this is not what we want since the namespaces may be
attached to other controllers as well.

This patch adds an additional NvmeBus on the subsystem device. When
nvme-ns devices are realized, if the parent controller device is linked
to a subsystem, the parent bus is set to the subsystem one instead. This
makes sure that namespaces are kept alive and not unrealized.

Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
---
 hw/nvme/nvme.h   | 15 ++++++++-------
 hw/nvme/ctrl.c   | 14 ++++++--------
 hw/nvme/ns.c     | 18 ++++++++++++++++++
 hw/nvme/subsys.c |  3 +++
 4 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/hw/nvme/nvme.h b/hw/nvme/nvme.h
index c4065467d877..83ffabade4cf 100644
--- a/hw/nvme/nvme.h
+++ b/hw/nvme/nvme.h
@@ -33,12 +33,20 @@ QEMU_BUILD_BUG_ON(NVME_MAX_NAMESPACES > NVME_NSID_BROADCAST 
- 1);
 typedef struct NvmeCtrl NvmeCtrl;
 typedef struct NvmeNamespace NvmeNamespace;
+#define TYPE_NVME_BUS "nvme-bus"
+OBJECT_DECLARE_SIMPLE_TYPE(NvmeBus, NVME_BUS)
+
+typedef struct NvmeBus {
+    BusState parent_bus;
+} NvmeBus;
+
 #define TYPE_NVME_SUBSYS "nvme-subsys"
 #define NVME_SUBSYS(obj) \
     OBJECT_CHECK(NvmeSubsystem, (obj), TYPE_NVME_SUBSYS)
 typedef struct NvmeSubsystem {
     DeviceState parent_obj;
+    NvmeBus     bus;
     uint8_t     subnqn[256];
     NvmeCtrl      *ctrls[NVME_MAX_CONTROLLERS];
@@ -365,13 +373,6 @@ typedef struct NvmeCQueue {
     QTAILQ_HEAD(, NvmeRequest) req_list;
 } NvmeCQueue;
-#define TYPE_NVME_BUS "nvme-bus"
-#define NVME_BUS(obj) OBJECT_CHECK(NvmeBus, (obj), TYPE_NVME_BUS)
-
-typedef struct NvmeBus {
-    BusState parent_bus;
-} NvmeBus;
-
 #define TYPE_NVME "nvme"
 #define NVME(obj) \
         OBJECT_CHECK(NvmeCtrl, (obj), TYPE_NVME)
diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
index 90e3ee2b70ee..9a3b3a27c293 100644
--- a/hw/nvme/ctrl.c
+++ b/hw/nvme/ctrl.c
@@ -6514,16 +6514,14 @@ static void nvme_exit(PCIDevice *pci_dev)
     nvme_ctrl_reset(n);
-    for (i = 1; i <= NVME_MAX_NAMESPACES; i++) {
-        ns = nvme_ns(n, i);
-        if (!ns) {
-            continue;
+    if (n->subsys) {
+        for (i = 1; i <= NVME_MAX_NAMESPACES; i++) {
+            ns = nvme_ns(n, i);
+            if (ns) {
+                ns->attached--;
+            }
         }
-        nvme_ns_cleanup(ns);

So who is removing the namespaces, then?
I would have expected some cleanup action from the subsystem, seeing that we reparent to that ...


Since we "move" the namespaces to the subsystem, and since the subsystem is non-hotpluggable, they will (and can) not be removed. In the case that there is no subsystem, nvme_ns_unrealize() will be called for each child namespace on the controller NvmeBus.

-    }
-
-    if (n->subsys) {
         nvme_subsys_unregister_ctrl(n->subsys, n);
     }
diff --git a/hw/nvme/ns.c b/hw/nvme/ns.c
index 3c4f5b8c714a..b7cf1494e75b 100644
--- a/hw/nvme/ns.c
+++ b/hw/nvme/ns.c
@@ -441,6 +441,15 @@ void nvme_ns_cleanup(NvmeNamespace *ns)
     }
 }
+static void nvme_ns_unrealize(DeviceState *dev)
+{
+    NvmeNamespace *ns = NVME_NS(dev);
+
+    nvme_ns_drain(ns);
+    nvme_ns_shutdown(ns);
+    nvme_ns_cleanup(ns);
+}
+
 static void nvme_ns_realize(DeviceState *dev, Error **errp)
 {
     NvmeNamespace *ns = NVME_NS(dev);
@@ -462,6 +471,14 @@ static void nvme_ns_realize(DeviceState *dev, Error **errp)
                        "linked to an nvme-subsys device");
             return;
         }
+    } else {
+        /*
+         * If this namespace belongs to a subsystem (through a link on the
+         * controller device), reparent the device.
+         */
+        if (!qdev_set_parent_bus(dev, &subsys->bus.parent_bus, errp)) {
+            return;
+        }

What happens if that fails?
Will we abort? Not create the namespace?


Good point!

It can actually only fail if the bus implements check_address(), which it does not, so it always succeeds, so it should assert instead.

     }
     if (nvme_ns_setup(ns, errp)) {
@@ -552,6 +569,7 @@ static void nvme_ns_class_init(ObjectClass *oc, void *data)
     dc->bus_type = TYPE_NVME_BUS;
     dc->realize = nvme_ns_realize;
+    dc->unrealize = nvme_ns_unrealize;
     device_class_set_props(dc, nvme_ns_props);
     dc->desc = "Virtual NVMe namespace";
 }
diff --git a/hw/nvme/subsys.c b/hw/nvme/subsys.c
index 92caa604a280..93c35950d69d 100644
--- a/hw/nvme/subsys.c
+++ b/hw/nvme/subsys.c
@@ -50,6 +50,9 @@ static void nvme_subsys_realize(DeviceState *dev, Error 
**errp)
 {
     NvmeSubsystem *subsys = NVME_SUBSYS(dev);
+    qbus_create_inplace(&subsys->bus, sizeof(NvmeBus), TYPE_NVME_BUS, dev,
+                        dev->id);
+
     nvme_subsys_setup(subsys);
 }

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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