When a new subchannel offer from host comes during device shutdown (e.g.
when a netvsc/storvsc module is unloadedshortly after it was loaded) a
crash can happen as vmbus_process_offer() is not anyhow serialized with
vmbus_remove(). As an example we can try calling subchannel create
callback when the module is already unloaded.
The following crash was observed while keeping loading/unloading hv_netvsc
module on 64-CPU guest:
hv_netvsc vmbus_14: net device safe to remove
BUG: unable to handle kernel paging request at 000000000000a118
IP: [<ffffffffa01c1b21>] netvsc_sc_open+0x31/0xb0 [hv_netvsc]
PGD 1f3946a067 PUD 1f38a5f067 PMD 0
Oops: 0000 [#1] SMP
...
Call Trace:
[<ffffffffa0055cd7>] vmbus_onoffer+0x477/0x530 [hv_vmbus]
[<ffffffff81092e1f>] ? move_linked_works+0x5f/0x80
[<ffffffffa0055fd3>] vmbus_onmessage+0x33/0xa0 [hv_vmbus]
[<ffffffffa0052f81>] vmbus_onmessage_work+0x21/0x30 [hv_vmbus]
[<ffffffff81095cde>] process_one_work+0x18e/0x4e0
...
The issue cannot be solved by just resetting sc_creation_callback on
driver removal as while we search for the parent channel with channel_lock
held we release it after the channel was found and it can disapper beneath
our feet while we're still in vmbus_process_offer();
Introduce new sc_create_lock mutex and take it in vmbus_remove() to ensure
no new subchannels are created after we started the removal procedure.
Check its state with mutex_trylock in vmbus_process_offer().
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
drivers/hv/channel.c | 3 +++
drivers/hv/channel_mgmt.c | 20 ++++++++++++++++++--
drivers/hv/vmbus_drv.c | 6 ++++++
include/linux/hyperv.h | 4 ++++
4 files changed, 31 insertions(+), 2 deletions(-)
diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 603ce97..faa91fe 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -555,6 +555,9 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
if (channel->rescind)
hv_process_channel_removal(channel,
channel->offermsg.child_relid);
+ else if (mutex_is_locked(&channel->sc_create_lock))
+ mutex_unlock(&channel->sc_create_lock);
+
return ret;
}
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 4506a66..96f8b96 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -150,6 +150,8 @@ static struct vmbus_channel *alloc_channel(void)
INIT_LIST_HEAD(&channel->sc_list);
INIT_LIST_HEAD(&channel->percpu_list);
+ mutex_init(&channel->sc_create_lock);
+
return channel;
}
@@ -158,6 +160,7 @@ static struct vmbus_channel *alloc_channel(void)
*/
static void free_channel(struct vmbus_channel *channel)
{
+ mutex_destroy(&channel->sc_create_lock);
kfree(channel);
}
@@ -247,8 +250,18 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
newchannel->offermsg.offer.if_type) &&
!uuid_le_cmp(channel->offermsg.offer.if_instance,
newchannel->offermsg.offer.if_instance)) {
- fnew = false;
- break;
+ if (mutex_trylock(&channel->sc_create_lock)) {
+ fnew = false;
+ break;
+ }
+ /*
+ * If we fail to acquire mutex here it means we're
+ * closing parent channel at this moment. We can't
+ * create new subchannel in this case.
+ */
+ spin_unlock_irqrestore(&vmbus_connection.channel_lock,
+ flags);
+ goto err_free_chan;
}
}
@@ -297,6 +310,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
if (!fnew) {
if (channel->sc_creation_callback != NULL)
channel->sc_creation_callback(newchannel);
+ mutex_unlock(&channel->sc_create_lock);
return;
}
@@ -340,6 +354,8 @@ err_deq_chan:
}
err_free_chan:
+ if (!fnew)
+ mutex_unlock(&channel->sc_create_lock);
free_channel(newchannel);
}
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index cf20400..7ad7fcc 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -539,6 +539,12 @@ static int vmbus_remove(struct device *child_device)
struct hv_device *dev = device_to_hv_device(child_device);
u32 relid = dev->channel->offermsg.child_relid;
+ /*
+ * Device is being removed, prevent creating new subchannels. Mutex
+ * will be released in vmbus_close_internal().
+ */
+ mutex_lock(&dev->channel->sc_create_lock);
+
if (child_device->driver) {
drv = drv_to_hv_drv(child_device->driver);
if (drv->remove)
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 30d3a1f..f1af05c 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -748,6 +748,10 @@ struct vmbus_channel {
*/
struct vmbus_channel *primary_channel;
/*
+ * Protects sub-channel create path.
+ */
+ struct mutex sc_create_lock;
+ /*
* Support per-channel state for use by vmbus drivers.
*/
void *per_channel_state;
--
2.4.3
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