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 <[email protected]>
---
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
> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:[email protected]]
> Sent: Monday, July 13, 2015 5:19 AM
> To: [email protected]
> Cc: KY Srinivasan; Haiyang Zhang; Dexuan Cui; [email protected]
> Subject: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation on
> device shutdown
>
> 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 <[email protected]>
Thanks Vitaly; strangely enough, I too am looking at this exact problem. I was planning to
address this problem a little differently: I was planning to hold the context that performed
the initial (primary) channel open until all of the "open activity" was completed and this would include
opening of the sub-channels for multi-channel devices.
Regards,
K. Y
> ---
> 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
KY Srinivasan <[email protected]> writes:
>> -----Original Message-----
>> From: Vitaly Kuznetsov [mailto:[email protected]]
>> Sent: Monday, July 13, 2015 5:19 AM
>> To: [email protected]
>> Cc: KY Srinivasan; Haiyang Zhang; Dexuan Cui; [email protected]
>> Subject: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation on
>> device shutdown
>>
>> 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 <[email protected]>
>
> Thanks Vitaly; strangely enough, I too am looking at this exact problem. I was planning to
> address this problem a little differently: I was planning to hold the context that performed
> the initial (primary) channel open until all of the "open activity" was completed and this would include
> opening of the sub-channels for multi-channel devices.
(not sure it can actually happen with current implementation of Hyper-V
host but) in case a subchannel is rescinded and reopened again later on
such 'full open lock' won't probably help but in other cases both
approaches should give us equal results. This is not a hotpath, any
syncronization should do the job.
>
> Regards,
>
> K. Y
>
>> ---
>> 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
--
Vitaly
> -----Original Message-----
> From: Vitaly Kuznetsov
> Sent: Monday, July 13, 2015 20:19
> Subject: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation on device
> shutdown
>
> 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().
How about vmbus_onoffer_rescind()?
It's not serialized with vmbus_remove() either, so I think there is an issue too?
I remember when 'rmmod hv_netvsc', we get a rescind-offer message for
each subchannel.
> 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().
In my 8-CPU VM, I can very easily reproduce the panic by
1. running
while ((1)); do modprobe -r hv_netvsc; modprobe hv_netvsc; sleep 10; done.
and
2. in vmbus_onoffer_rescind(), we sleep 3s after a subchannel is added into
the primary channel's sc_list (and before the sc_creation_callback is invoked):
(I added line 275)
262 if (!fnew) {
263 /*
264 * Check to see if this is a sub-channel.
265 */
266 if (newchannel->offermsg.offer.sub_channel_index != 0) {
267 /*
268 * Process the sub-channel.
269 */
270 newchannel->primary_channel = channel;
271 spin_lock_irqsave(&channel->lock, flags);
272 list_add_tail(&newchannel->sc_list, &channel->sc_list);
273 channel->num_sc++;
274 spin_unlock_irqrestore(&channel->lock, flags);
275 ssleep(3);
276 } else
277 goto err_free_chan;
278 }
Dexuan Cui <[email protected]> writes:
>> -----Original Message-----
>> From: Vitaly Kuznetsov
>> Sent: Monday, July 13, 2015 20:19
>> Subject: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation on device
>> shutdown
>>
>> 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().
>
> How about vmbus_onoffer_rescind()?
> It's not serialized with vmbus_remove() either, so I think there is an issue too?
>
> I remember when 'rmmod hv_netvsc', we get a rescind-offer message for
> each subchannel.
>
True, I think we have a race with rescind messages as well, we just
never saw crashes for some reason. I'll think how we can make the fix
more general.
>> 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().
>
> In my 8-CPU VM, I can very easily reproduce the panic by
> 1. running
> while ((1)); do modprobe -r hv_netvsc; modprobe hv_netvsc; sleep 10; done.
>
> and
> 2. in vmbus_onoffer_rescind(), we sleep 3s after a subchannel is added into
> the primary channel's sc_list (and before the sc_creation_callback is invoked):
> (I added line 275)
>
> 262 if (!fnew) {
> 263 /*
> 264 * Check to see if this is a sub-channel.
> 265 */
> 266 if (newchannel->offermsg.offer.sub_channel_index != 0) {
> 267 /*
> 268 * Process the sub-channel.
> 269 */
> 270 newchannel->primary_channel = channel;
> 271 spin_lock_irqsave(&channel->lock, flags);
> 272 list_add_tail(&newchannel->sc_list, &channel->sc_list);
> 273 channel->num_sc++;
> 274 spin_unlock_irqrestore(&channel->lock, flags);
> 275 ssleep(3);
> 276 } else
> 277 goto err_free_chan;
> 278 }
It is possible to see crashes even without such intrumentation, move
CPUs and slower host will do the job.
Thanks,
--
Vitaly
> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:[email protected]]
> Sent: Tuesday, July 14, 2015 9:03 AM
> To: Dexuan Cui
> Cc: [email protected]; KY Srinivasan; Haiyang Zhang; linux-
> [email protected]
> Subject: Re: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation
> on device shutdown
>
> Dexuan Cui <[email protected]> writes:
>
> >> -----Original Message-----
> >> From: Vitaly Kuznetsov
> >> Sent: Monday, July 13, 2015 20:19
> >> Subject: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation on
> device
> >> shutdown
> >>
> >> 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().
> >
> > How about vmbus_onoffer_rescind()?
> > It's not serialized with vmbus_remove() either, so I think there is an issue
> too?
> >
> > I remember when 'rmmod hv_netvsc', we get a rescind-offer message for
> > each subchannel.
> >
>
> True, I think we have a race with rescind messages as well, we just
> never saw crashes for some reason. I'll think how we can make the fix
> more general.
In an earlier email I had outlined how I was planning to address original issue. I have a patch based on the logic
I had described - essentially put the burden on the probe call to ensure that the open (including sub-channels) is
complete before we return from probe. I will post this shortly.
Regards,
K. Y
> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:[email protected]]
> Sent: Tuesday, July 14, 2015 9:03 AM
> To: Dexuan Cui
> Cc: [email protected]; KY Srinivasan; Haiyang Zhang; linux-
> [email protected]
> Subject: Re: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation
> on device shutdown
>
> Dexuan Cui <[email protected]> writes:
>
> >> -----Original Message-----
> >> From: Vitaly Kuznetsov
> >> Sent: Monday, July 13, 2015 20:19
> >> Subject: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation on
> device
> >> shutdown
> >>
> >> 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().
> >
> > How about vmbus_onoffer_rescind()?
> > It's not serialized with vmbus_remove() either, so I think there is an issue
> too?
> >
> > I remember when 'rmmod hv_netvsc', we get a rescind-offer message for
> > each subchannel.
> >
>
> True, I think we have a race with rescind messages as well, we just
> never saw crashes for some reason. I'll think how we can make the fix
> more general.
In an earlier email I had outlined how I was planning to address original issue. I have a patch based on the logic
I had described - essentially put the burden on the probe call to ensure that the open (including sub-channels) is
complete before we return from probe. I will post this shortly.
Regards,
K. Y