Drivers: hv: vmbus: Offload the handling of channels to two workqueues

vmbus_process_offer() mustn't call channel->sc_creation_callback()
directly for sub-channels, because sc_creation_callback() ->
vmbus_open() may never get the host's response to the
OPEN_CHANNEL message (the host may rescind a channel at any time,
e.g. in the case of hot removing a NIC), and vmbus_onoffer_rescind()
may not wake up the vmbus_open() as it's blocked due to a non-zero
vmbus_connection.offer_in_progress, and finally we have a deadlock.

The above is also true for primary channels, if the related device
drivers use sync probing mode by default.

And, usually the handling of primary channels and sub-channels can
depend on each other, so we should offload them to different
workqueues to avoid possible deadlock, e.g. in sync-probing mode,
NIC1's netvsc_subchan_work() can race with NIC2's netvsc_probe() ->
rtnl_lock(), and causes deadlock: the former gets the rtnl_lock
and waits for all the sub-channels to appear, but the latter
can't get the rtnl_lock and this blocks the handling of sub-channels.

The patch can fix the multiple-NIC deadlock described above for
v3.x kernels (e.g. RHEL 7.x) which don't support async-probing
of devices, and v4.4, v4.9, v4.14 and v4.18 which support async-probing
but don't enable async-probing for Hyper-V drivers (yet).

The patch can also fix the hang issue in sub-channel's handling described
above for all versions of kernels, including v4.19 and v4.20-rc4.

So actually the patch should be applied to all the existing kernels,
not only the kernels that have 8195b1396ec8.

Fixes: 8195b1396ec8 ("hv_netvsc: fix deadlock on hotplug")
Cc: stable@vger.kernel.org
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 161 insertions, 66 deletions

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 6277597d3d58..edd34c167a9b 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -435,61 +435,16 @@ void vmbus_free_channels(void)
         }
 }
 
-/*
- * vmbus_process_offer - Process the offer by creating a channel/device
- * associated with this offer
- */
-static void vmbus_process_offer(struct vmbus_channel *newchannel)
+/* Note: the function can run concurrently for primary/sub channels. */
+static void vmbus_add_channel_work(struct work_struct *work)
 {
-        struct vmbus_channel *channel;
-        bool fnew = true;
+        struct vmbus_channel *newchannel =
+                container_of(work, struct vmbus_channel, add_channel_work);
+        struct vmbus_channel *primary_channel = newchannel->primary_channel;
         unsigned long flags;
         u16 dev_type;
         int ret;
 
-        /* Make sure this is a new offer */
-        mutex_lock(&vmbus_connection.channel_mutex);
-
-        /*
-         * Now that we have acquired the channel_mutex,
-         * we can release the potentially racing rescind thread.
-         */
-        atomic_dec(&vmbus_connection.offer_in_progress);
-
-        list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
-                if (!uuid_le_cmp(channel->offermsg.offer.if_type,
-                        newchannel->offermsg.offer.if_type) &&
-                        !uuid_le_cmp(channel->offermsg.offer.if_instance,
-                                newchannel->offermsg.offer.if_instance)) {
-                        fnew = false;
-                        break;
-                }
-        }
-
-        if (fnew)
-                list_add_tail(&newchannel->listentry,
-                              &vmbus_connection.chn_list);
-
-        mutex_unlock(&vmbus_connection.channel_mutex);
-
-        if (!fnew) {
-                /*
-                 * Check to see if this is a sub-channel.
-                 */
-                if (newchannel->offermsg.offer.sub_channel_index != 0) {
-                        /*
-                         * Process the sub-channel.
-                         */
-                        newchannel->primary_channel = channel;
-                        spin_lock_irqsave(&channel->lock, flags);
-                        list_add_tail(&newchannel->sc_list, &channel->sc_list);
-                        channel->num_sc++;
-                        spin_unlock_irqrestore(&channel->lock, flags);
-                } else {
-                        goto err_free_chan;
-                }
-        }
-
         dev_type = hv_get_dev_type(newchannel);
 
         init_vp_index(newchannel, dev_type);
@@ -507,27 +462,26 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
         /*
          * This state is used to indicate a successful open
          * so that when we do close the channel normally, we
-         * can cleanup properly
+         * can cleanup properly.
          */
         newchannel->state = CHANNEL_OPEN_STATE;
 
-        if (!fnew) {
-                struct hv_device *dev
-                        = newchannel->primary_channel->device_obj;
+        if (primary_channel != NULL) {
+                /* newchannel is a sub-channel. */
+                struct hv_device *dev = primary_channel->device_obj;
 
                 if (vmbus_add_channel_kobj(dev, newchannel))
-                        goto err_free_chan;
+                        goto err_deq_chan;
+
+                if (primary_channel->sc_creation_callback != NULL)
+                        primary_channel->sc_creation_callback(newchannel);
 
-                if (channel->sc_creation_callback != NULL)
-                        channel->sc_creation_callback(newchannel);
                 newchannel->probe_done = true;
                 return;
         }
 
         /*
-         * Start the process of binding this offer to the driver
-         * We need to set the DeviceObject field before calling
-         * vmbus_child_dev_add()
+         * Start the process of binding the primary channel to the driver
          */
         newchannel->device_obj = vmbus_device_create(
                 &newchannel->offermsg.offer.if_type,
@@ -556,13 +510,28 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 
 err_deq_chan:
         mutex_lock(&vmbus_connection.channel_mutex);
-        list_del(&newchannel->listentry);
+
+        /*
+         * We need to set the flag, otherwise
+         * vmbus_onoffer_rescind() can be blocked.
+         */
+        newchannel->probe_done = true;
+
+        if (primary_channel == NULL) {
+                list_del(&newchannel->listentry);
+        } else {
+                spin_lock_irqsave(&primary_channel->lock, flags);
+                list_del(&newchannel->sc_list);
+                spin_unlock_irqrestore(&primary_channel->lock, flags);
+        }
+
         mutex_unlock(&vmbus_connection.channel_mutex);
 
         if (newchannel->target_cpu != get_cpu()) {
                 put_cpu();
                 smp_call_function_single(newchannel->target_cpu,
-                                         percpu_channel_deq, newchannel, true);
+                                         percpu_channel_deq,
+                                         newchannel, true);
         } else {
                 percpu_channel_deq(newchannel);
                 put_cpu();
@@ -570,14 +539,104 @@ err_deq_chan:
 
         vmbus_release_relid(newchannel->offermsg.child_relid);
 
-err_free_chan:
         free_channel(newchannel);
 }
 
 /*
+ * vmbus_process_offer - Process the offer by creating a channel/device
+ * associated with this offer
+ */
+static void vmbus_process_offer(struct vmbus_channel *newchannel)
+{
+        struct vmbus_channel *channel;
+        struct workqueue_struct *wq;
+        unsigned long flags;
+        bool fnew = true;
+
+        mutex_lock(&vmbus_connection.channel_mutex);
+
+        /*
+         * Now that we have acquired the channel_mutex,
+         * we can release the potentially racing rescind thread.
+         */
+        atomic_dec(&vmbus_connection.offer_in_progress);
+
+        list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
+                if (!uuid_le_cmp(channel->offermsg.offer.if_type,
+                                 newchannel->offermsg.offer.if_type) &&
+                    !uuid_le_cmp(channel->offermsg.offer.if_instance,
+                                 newchannel->offermsg.offer.if_instance)) {
+                        fnew = false;
+                        break;
+                }
+        }
+
+        if (fnew)
+                list_add_tail(&newchannel->listentry,
+                              &vmbus_connection.chn_list);
+        else {
+                /*