RE: [PATCH] Drivers: hv: vmbus: prevent new subchannel creation on device shutdown
From: KY Srinivasan
Date: Mon Jul 13 2015 - 11:10:46 EST
> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx]
> Sent: Monday, July 13, 2015 5:19 AM
> To: devel@xxxxxxxxxxxxxxxxxxxxxx
> Cc: KY Srinivasan; Haiyang Zhang; Dexuan Cui; linux-kernel@xxxxxxxxxxxxxxx
> 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 <vkuznets@xxxxxxxxxx>
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
--
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