Drivers: hv: vmbus: Perform device register in the per-channel work element

This patch is a continuation of the rescind handling cleanup work. We cannot
block in the global message handling work context especially if we are blocking
waiting for the host to wake us up. I would like to thank
Dexuan Cui <decui@microsoft.com> for observing this problem.

The current char-next branch is broken and this patch fixes
the bug.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 107 insertions, 44 deletions

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 611789139f9b..5f8e47bf5ccc 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -23,6 +23,7 @@
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
+#include <linux/delay.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/list.h>
@@ -37,6 +38,10 @@ struct vmbus_channel_message_table_entry {
         void (*message_handler)(struct vmbus_channel_message_header *msg);
 };
 
+struct vmbus_rescind_work {
+        struct work_struct work;
+        struct vmbus_channel *channel;
+};
 
 /**
  * vmbus_prep_negotiate_resp() - Create default response for Hyper-V Negotiate message
@@ -134,20 +139,6 @@ fw_error:
 
 EXPORT_SYMBOL_GPL(vmbus_prep_negotiate_resp);
 
-static void vmbus_process_device_unregister(struct work_struct *work)
-{
-        struct device *dev;
-        struct vmbus_channel *channel = container_of(work,
-                                                        struct vmbus_channel,
-                                                        work);
-
-        dev = get_device(&channel->device_obj->device);
-        if (dev) {
-                vmbus_device_unregister(channel->device_obj);
-                put_device(dev);
-        }
-}
-
 static void vmbus_sc_creation_cb(struct work_struct *work)
 {
         struct vmbus_channel *newchannel = container_of(work,
@@ -220,6 +211,40 @@ static void free_channel(struct vmbus_channel *channel)
         queue_work(vmbus_connection.work_queue, &channel->work);
 }
 
+static void process_rescind_fn(struct work_struct *work)
+{
+        struct vmbus_rescind_work *rc_work;
+        struct vmbus_channel *channel;
+        struct device *dev;
+
+        rc_work = container_of(work, struct vmbus_rescind_work, work);
+        channel = rc_work->channel;
+
+        /*
+         * We have already acquired a reference on the channel
+         * and so it cannot vanish underneath us.
+         * It is possible (while very unlikely) that we may
+         * get here while the processing of the initial offer
+         * is still not complete. Deal with this situation by
+         * just waiting until the channel is in the correct state.
+         */
+
+        while (channel->work.func != release_channel)
+                msleep(1000);
+
+        if (channel->device_obj) {
+                dev = get_device(&channel->device_obj->device);
+                if (dev) {
+                        vmbus_device_unregister(channel->device_obj);
+                        put_device(dev);
+                }
+        } else {
+                hv_process_channel_removal(channel,
+                                           channel->offermsg.child_relid);
+        }
+        kfree(work);
+}
+
 static void percpu_channel_enq(void *arg)
 {
         struct vmbus_channel *channel = arg;
@@ -282,6 +307,46 @@ void vmbus_free_channels(void)
         }
 }
 
+static void vmbus_do_device_register(struct work_struct *work)
+{
+        struct hv_device *device_obj;
+        int ret;
+        unsigned long flags;
+        struct vmbus_channel *newchannel = container_of(work,
+                                                     struct vmbus_channel,
+                                                     work);
+
+        ret = vmbus_device_register(newchannel->device_obj);
+        if (ret != 0) {
+                pr_err("unable to add child device object (relid %d)\n",
+                        newchannel->offermsg.child_relid);
+                spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
+                list_del(&newchannel->listentry);
+                device_obj = newchannel->device_obj;
+                newchannel->device_obj = NULL;
+                spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);
+
+                if (newchannel->target_cpu != get_cpu()) {
+                        put_cpu();
+                        smp_call_function_single(newchannel->target_cpu,
+                                         percpu_channel_deq, newchannel, true);
+                } else {
+                        percpu_channel_deq(newchannel);
+                        put_cpu();
+                }
+
+                kfree(device_obj);
+                if (!newchannel->rescind) {
+                        free_channel(newchannel);
+                        return;
+                }
+        }
+        /*
+         * The next state for this channel is to be freed.
+         */
+        INIT_WORK(&newchannel->work, release_channel);
+}
+
 /*
  * vmbus_process_offer - Process the offer by creating a channel/device
  * associated with this offer
@@ -291,7 +356,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
         struct vmbus_channel *channel;
         bool fnew = true;
         bool enq = false;
-        int ret;
         unsigned long flags;
 
         /* Make sure this is a new offer */
@@ -393,16 +457,13 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
          * Add the new device to the bus. This will kick off device-driver
          * binding which eventually invokes the device driver's AddDevice()
          * method.
+         * Invoke this call on the per-channel work context.
+         * Until we return from this function, rescind offer message
+         * cannot be processed as we are running on the global message
+         * handling work.
          */
-        ret = vmbus_device_register(newchannel->device_obj);
-        if (ret != 0) {
-                pr_err("unable to add child device object (relid %d)\n",
-                           newchannel->offermsg.child_relid);
-
-                kfree(newchannel->device_obj);
-                goto err_deq_chan;
-        }
-
+        INIT_WORK(&newchannel->work, vmbus_do_device_register);
+        queue_work(newchannel->controlwq, &newchannel->work);
         return;
 
 err_deq_chan:
@@ -556,33 +617,31 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
 {
         struct vmbus_channel_rescind_offer *rescind;
         struct vmbus_channel *channel;
-        unsigned long flags;
+        struct vmbus_rescind_work *rc_work;
 
         rescind = (struct vmbus_channel_rescind_offer *)hdr;
-        channel = relid2channel(rescind->child_relid);
+        channel = relid2channel(rescind->child_relid, true);
 
         if (channel == NULL) {
                 hv_process_channel_removal(NULL, rescind->child_relid);
                 return;
         }
 
-        spin_lock_irqsave(&channel->lock, flags);
-        channel->rescind = true;
-        spin_unlock_irqrestore(&channel->lock, flags);
-
-        if (channel->device_obj) {
-                /*
-                 * We will have to unregister this device from the
-                 * driver core. Do this in the per-channel work context.
-                 * Note that we are currently executing on the global
-                 * workq for handling messages from the host.
-                 */
-                INIT_WORK(&channel->work, vmbus_process_device_unregister);
-                queue_work(channel->controlwq, &channel->work);
-        } else {
-                hv_process_channel_removal(channel,
-                                           channel->offermsg.child_relid);
+        /*
+         * We have acquired a reference on the channel and have posted
+         * the rescind state. Perform further cleanup in a work context
+         * that is different from the global work context in which
+         * we process messages from the host (we are currently executing
+         * on that global context.
+         */
+        rc_work = kzalloc(sizeof(struct vmbus_rescind_work), GFP_KERNEL);
+        if (!rc_work) {
+                pr_err("Unable to allocate memory for rescind processing ");
+                return;
         }
+        rc_work->channel = channel;
+        INIT_WORK(&rc_work->work, process_rescind_fn);
+        schedule_work(&rc_work->work);
 }
 
 /*
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 583d7d42b46d..8bcd3071c84f 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -270,7 +270,7 @@ static struct vmbus_channel *pcpu_relid2channel(u32 relid)
  * relid2channel - Get the channel object given its
  * child relative id (ie channel id)
  */
-struct vmbus_channel *relid2channel(u32 relid)
+struct vmbus_channel *relid2channel(u32 relid, bool rescind)
 {
         struct vmbus_channel *channel;
         struct vmbus_channel *found_channel  = NULL;
@@ -282,6 +282,8 @@ struct vmbus_channel *relid2channel(u32 relid)
         list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
                 if (channel->offermsg.child_relid == relid) {
                         found_channel = channel;
+                        if (rescind)
+                                found_channel->rescind = true;
                         break;
                 } else if (!list_empty(&channel->sc_list)) {
                         /*
@@ -292,6 +294,8 @@ struct vmbus_channel *relid2channel(u32 relid)
                                                         sc_list);
                                 if (cur_sc->offermsg.child_relid == relid) {
                                         found_channel = cur_sc;
+                                        if (rescind)
+                                                found_channel->rescind = true;
                                         break;
                                 }
                         }
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 88af4ec559c4..63395896baf9 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -698,7 +698,7 @@ void vmbus_device_unregister(struct hv_device *device_obj);
 /* VmbusChildDeviceDestroy( */
 /* struct hv_device *); */
 
-struct vmbus_channel *relid2channel(u32 relid);
+struct vmbus_channel *relid2channel(u32 relid, bool rescind);
 
 void vmbus_free_channels(void);