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Commit c9675904 authored by Dexuan Cui's avatar Dexuan Cui Committed by Martin K. Petersen
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scsi: storvsc: Fix a race in sub-channel creation that can cause panic 



We can concurrently try to open the same sub-channel from 2 paths:

path #1: vmbus_onoffer() -> vmbus_process_offer() -> handle_sc_creation().
path #2: storvsc_probe() -> storvsc_connect_to_vsp() ->
	 -> storvsc_channel_init() -> handle_multichannel_storage() ->
	 -> vmbus_are_subchannels_present() -> handle_sc_creation().

They conflict with each other, but it was not an issue before the recent
commit ae6935ed ("vmbus: split ring buffer allocation from open"),
because at the beginning of vmbus_open() we checked newchannel->state so
only one path could succeed, and the other would return with -EINVAL.

After ae6935ed, the failing path frees the channel's ringbuffer by
vmbus_free_ring(), and this causes a panic later.

Commit ae6935ed itself is good, and it just reveals the longstanding
race. We can resolve the issue by removing path #2, i.e. removing the
second vmbus_are_subchannels_present() in handle_multichannel_storage().

BTW, the comment "Check to see if sub-channels have already been created"
in handle_multichannel_storage() is incorrect: when we unload the driver,
we first close the sub-channel(s) and then close the primary channel, next
the host sends rescind-offer message(s) so primary->sc_list will become
empty. This means the first vmbus_are_subchannels_present() in
handle_multichannel_storage() is never useful.

Fixes: ae6935ed ("vmbus: split ring buffer allocation from open")
Cc: stable@vger.kernel.org
Cc: Long Li <longli@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: default avatarDexuan Cui <decui@microsoft.com>
Signed-off-by: default avatarK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent 02f425f8

drivers/scsi/storvsc_drv.c

+30 −31
Original line number Diff line number Diff line
@@ -446,7 +446,6 @@ struct storvsc_device { 


	bool	 destroy;

	bool	 drain_notify;

	bool	 open_sub_channel;

	atomic_t num_outstanding_req;

	struct Scsi_Host *host;
@@ -636,33 +635,38 @@ static inline struct storvsc_device *get_in_stor_device( 
static void handle_sc_creation(struct vmbus_channel *new_sc)

{

	struct hv_device *device = new_sc->primary_channel->device_obj;

	struct device *dev = &device->device;

	struct storvsc_device *stor_device;

	struct vmstorage_channel_properties props;

	int ret;



	stor_device = get_out_stor_device(device);

	if (!stor_device)

		return;



	if (stor_device->open_sub_channel == false)

		return;



	memset(&props, 0, sizeof(struct vmstorage_channel_properties));



	vmbus_open(new_sc,

	ret = vmbus_open(new_sc,

			 storvsc_ringbuffer_size,

			 storvsc_ringbuffer_size,

			 (void *)&props,

			 sizeof(struct vmstorage_channel_properties),

			 storvsc_on_channel_callback, new_sc);



	if (new_sc->state == CHANNEL_OPENED_STATE) {

	/* In case vmbus_open() fails, we don't use the sub-channel. */

	if (ret != 0) {

		dev_err(dev, "Failed to open sub-channel: err=%d\n", ret);

		return;

	}



	/* Add the sub-channel to the array of available channels. */

	stor_device->stor_chns[new_sc->target_cpu] = new_sc;

	cpumask_set_cpu(new_sc->target_cpu, &stor_device->alloced_cpus);

}

}



static void  handle_multichannel_storage(struct hv_device *device, int max_chns)

{

	struct device *dev = &device->device;

	struct storvsc_device *stor_device;

	int num_cpus = num_online_cpus();

	int num_sc;
@@ -679,21 +683,11 @@ static void handle_multichannel_storage(struct hv_device *device, int max_chns) 
	request = &stor_device->init_request;

	vstor_packet = &request->vstor_packet;



	stor_device->open_sub_channel = true;

	/*

	 * Establish a handler for dealing with subchannels.

	 */

	vmbus_set_sc_create_callback(device->channel, handle_sc_creation);



	/*

	 * Check to see if sub-channels have already been created. This

	 * can happen when this driver is re-loaded after unloading.

	 */



	if (vmbus_are_subchannels_present(device->channel))

		return;



	stor_device->open_sub_channel = false;

	/*

	 * Request the host to create sub-channels.

	 */
@@ -710,23 +704,29 @@ static void handle_multichannel_storage(struct hv_device *device, int max_chns) 
			       VM_PKT_DATA_INBAND,

			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);



	if (ret != 0)

	if (ret != 0) {

		dev_err(dev, "Failed to create sub-channel: err=%d\n", ret);

		return;

	}



	t = wait_for_completion_timeout(&request->wait_event, 10*HZ);

	if (t == 0)

	if (t == 0) {

		dev_err(dev, "Failed to create sub-channel: timed out\n");

		return;

	}



	if (vstor_packet->operation != VSTOR_OPERATION_COMPLETE_IO ||

	    vstor_packet->status != 0)

	    vstor_packet->status != 0) {

		dev_err(dev, "Failed to create sub-channel: op=%d, sts=%d\n",

			vstor_packet->operation, vstor_packet->status);

		return;

	}



	/*

	 * Now that we created the sub-channels, invoke the check; this

	 * may trigger the callback.

	 * We need to do nothing here, because vmbus_process_offer()

	 * invokes channel->sc_creation_callback, which will open and use

	 * the sub-channel(s).

	 */

	stor_device->open_sub_channel = true;

	vmbus_are_subchannels_present(device->channel);

}



static void cache_wwn(struct storvsc_device *stor_device,
@@ -1794,7 +1794,6 @@ static int storvsc_probe(struct hv_device *device, 
	}



	stor_device->destroy = false;

	stor_device->open_sub_channel = false;

	init_waitqueue_head(&stor_device->waiting_to_drain);

	stor_device->device = device;

	stor_device->host = host;