Drivers: hv: vmbus: Reset the channel callback in vmbus_onoffer_rescind()

Before setting channel->rescind in vmbus_rescind_cleanup(), we should make
sure the channel callback won't run any more, otherwise a high-level
driver like pci_hyperv, which may be infinitely waiting for the host VSP's
response and notices the channel has been rescinded, can't safely give
up: e.g., in hv_pci_protocol_negotiation() -> wait_for_response(), it's
unsafe to exit from wait_for_response() and proceed with the on-stack
variable "comp_pkt" popped. The issue was originally spotted by
Michael Kelley <mikelley@microsoft.com>.

In vmbus_close_internal(), the patch also minimizes the range protected by
disabling/enabling channel->callback_event: we don't really need that for
the whole function.
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Cc: stable@vger.kernel.org
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/channel.c

@@ -558,11 +558,8 @@ static void reset_channel_cb(void *arg)
 	channel->onchannel_callback = NULL;
 }
 
-static int vmbus_close_internal(struct vmbus_channel *channel)
+void vmbus_reset_channel_cb(struct vmbus_channel *channel)
 {
-	struct vmbus_channel_close_channel *msg;
-	int ret;
-
 	/*
 	 * vmbus_on_event(), running in the per-channel tasklet, can race
 	 * with vmbus_close_internal() in the case of SMP guest, e.g., when
@@ -572,6 +569,29 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
 	 */
 	tasklet_disable(&channel->callback_event);
 
+	channel->sc_creation_callback = NULL;
+
+	/* Stop the callback asap */
+	if (channel->target_cpu != get_cpu()) {
+		put_cpu();
+		smp_call_function_single(channel->target_cpu, reset_channel_cb,
+					 channel, true);
+	} else {
+		reset_channel_cb(channel);
+		put_cpu();
+	}
+
+	/* Re-enable tasklet for use on re-open */
+	tasklet_enable(&channel->callback_event);
+}
+
+static int vmbus_close_internal(struct vmbus_channel *channel)
+{
+	struct vmbus_channel_close_channel *msg;
+	int ret;
+
+	vmbus_reset_channel_cb(channel);
+
 	/*
 	 * In case a device driver's probe() fails (e.g.,
 	 * util_probe() -> vmbus_open() returns -ENOMEM) and the device is
@@ -585,16 +605,6 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
 	}
 
 	channel->state = CHANNEL_OPEN_STATE;
-	channel->sc_creation_callback = NULL;
-	/* Stop callback and cancel the timer asap */
-	if (channel->target_cpu != get_cpu()) {
-		put_cpu();
-		smp_call_function_single(channel->target_cpu, reset_channel_cb,
-					 channel, true);
-	} else {
-		reset_channel_cb(channel);
-		put_cpu();
-	}
 
 	/* Send a closing message */
 
@@ -639,8 +649,6 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
 		get_order(channel->ringbuffer_pagecount * PAGE_SIZE));
 
 out:
-	/* re-enable tasklet for use on re-open */
-	tasklet_enable(&channel->callback_event);
 	return ret;
 }
 

drivers/hv/channel_mgmt.c

@@ -892,6 +892,12 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
 		return;
 	}
 
+	/*
+	 * Before setting channel->rescind in vmbus_rescind_cleanup(), we
+	 * should make sure the channel callback is not running any more.
+	 */
+	vmbus_reset_channel_cb(channel);
+
 	/*
 	 * Now wait for offer handling to complete.
 	 */

include/linux/hyperv.h

@@ -1061,6 +1061,8 @@ extern int vmbus_establish_gpadl(struct vmbus_channel *channel,
 extern int vmbus_teardown_gpadl(struct vmbus_channel *channel,
 				     u32 gpadl_handle);
 
+void vmbus_reset_channel_cb(struct vmbus_channel *channel);
+
 extern int vmbus_recvpacket(struct vmbus_channel *channel,
 				  void *buffer,
 				  u32 bufferlen,