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[PATCH 06/11] Drivers: hv: vmbus: serialize process_chn_event() and vmbus_close_internal()

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From: Dexuan Cui <decui@microsoft.com>

process_chn_event(), running in the tasklet, can race with
vmbus_close_internal() in the case of SMP guest, e.g., when the former is
accessing channel->inbound.ring_buffer, the latter could be freeing the
ring_buffer pages.

To resolve the race, we can serialize them by disabling the tasklet when
the latter is running here.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
 drivers/hv/channel.c |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index c4dcab0..f7f3d5c 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -28,6 +28,7 @@
 #include <linux/module.h>
 #include <linux/hyperv.h>
 #include <linux/uio.h>
+#include <linux/interrupt.h>
 
 #include "hyperv_vmbus.h"
 
@@ -496,8 +497,21 @@ static void reset_channel_cb(void *arg)
 static int vmbus_close_internal(struct vmbus_channel *channel)
 {
 	struct vmbus_channel_close_channel *msg;
+	struct tasklet_struct *tasklet;
 	int ret;
 
+	/*
+	 * process_chn_event(), running in the tasklet, can race
+	 * with vmbus_close_internal() in the case of SMP guest, e.g., when
+	 * the former is accessing channel->inbound.ring_buffer, the latter
+	 * could be freeing the ring_buffer pages.
+	 *
+	 * To resolve the race, we can serialize them by disabling the
+	 * tasklet when the latter is running here.
+	 */
+	tasklet = hv_context.event_dpc[channel->target_cpu];
+	tasklet_disable(tasklet);
+
 	channel->state = CHANNEL_OPEN_STATE;
 	channel->sc_creation_callback = NULL;
 	/* Stop callback and cancel the timer asap */
@@ -525,7 +539,7 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
 		 * If we failed to post the close msg,
 		 * it is perhaps better to leak memory.
 		 */
-		return ret;
+		goto out;
 	}
 
 	/* Tear down the gpadl for the channel's ring buffer */
@@ -538,7 +552,7 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
 			 * If we failed to teardown gpadl,
 			 * it is perhaps better to leak memory.
 			 */
-			return ret;
+			goto out;
 		}
 	}
 
@@ -555,6 +569,9 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
 	if (channel->rescind)
 		hv_process_channel_removal(channel,
 					   channel->offermsg.child_relid);
+out:
+	tasklet_enable(tasklet);
+
 	return ret;
 }
 
-- 
1.7.4.1

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Thread

[PATCH 00/11] Drivers: hv: vmbus: Miscellaneous fixes and cleanup   "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
  [PATCH 02/11] Drivers: hv: vmbus: Use uuid_le type consistently "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
  [PATCH 06/11] Drivers: hv: vmbus: serialize process_chn_event() and vmbus_close_internal() "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
  [PATCH 03/11] Drivers: hv: vmbus: Use the macro for comparing GUIDs "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
    Re: [PATCH 03/11] Drivers: hv: vmbus: Use the macro for comparing GUIDs Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-11-11 09:40 +0100
      RE: [PATCH 03/11] Drivers: hv: vmbus: Use the macro for comparing  GUIDs KY Srinivasan <kys@microsoft.com> - 2015-11-11 18:40 +0100
  [PATCH 05/11] Drivers: hv: vmbus: Get rid of the unused irq variable "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
  [PATCH 08/11] Drivers: hv: vmbus: fix rescind-offer handling for device without a driver "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
  [PATCH 01/11] Drivers: hv: vss: run only on supported host versions "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
    [PATCH 10/11] Drivers: hv: vmbus: channge vmbus_connection.channel_lock to mutex "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
    [PATCH 07/11] Drivers: hv: vmbus: do sanity check of channel state in vmbus_close_internal() "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:30 +0100
    [PATCH 11/11] drivers:hv: Allow for MMIO claims that span ACPI _CRS records "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:40 +0100
    [PATCH 04/11] Drivers: hv: vmbus: Get rid of the unused macro "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:40 +0100
    [PATCH 09/11] Drivers: hv: vmbus: release relid on error in vmbus_process_offer() "K. Y. Srinivasan" <kys@microsoft.com> - 2015-11-11 01:40 +0100

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