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[PATCH RESEND 16/27] 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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[PATCH RESEND 01/27] Drivers: hv: util: Increase the timeout for util services "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:30 +0100
  [PATCH RESEND 02/27] Drivers: hv: utils: run polling callback always in interrupt context "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:30 +0100
  [PATCH RESEND 03/27] tools: hv: report ENOSPC errors in hv_fcopy_daemon "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:30 +0100
  [PATCH RESEND 06/27] Drivers: hv: utils: use memdup_user in hvt_op_write "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:30 +0100
  [PATCH RESEND 04/27] tools: hv: remove repeated HV_FCOPY string "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:30 +0100
  [PATCH RESEND 10/27] drivers:hv: Define the channel type for Hyper-V PCI Express pass-through "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 09/27] drivers:hv: Export the API to invoke a hypercall on Hyper-V "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
    Re: [PATCH RESEND 09/27] drivers:hv: Export the API to invoke a  hypercall on Hyper-V Greg KH <gregkh@linuxfoundation.org> - 2015-12-15 04:10 +0100
      RE: [PATCH RESEND 09/27] drivers:hv: Export the API to invoke a  hypercall on Hyper-V KY Srinivasan <kys@microsoft.com> - 2015-12-15 05:20 +0100
  [PATCH RESEND 14/27] Drivers: hv: vmbus: Get rid of the unused macro "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 20/27] Drivers: hv: vmbus: channge vmbus_connection.channel_lock to mutex "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 26/27] Drivers: hv: utils: Invoke the poll function after handshake "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 05/27] Drivers: hv: util: catch allocation errors "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 08/27] drivers:hv: Export a function that maps Linux CPU num onto Hyper-V proc num "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 07/27] drivers/hv: cleanup synic msrs if vmbus connect failed "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 22/27] tools/hv: Use include/uapi with __EXPORTED_HEADERS__ "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
    Re: [PATCH RESEND 22/27] tools/hv: Use include/uapi with  __EXPORTED_HEADERS__ Greg KH <gregkh@linuxfoundation.org> - 2015-12-15 04:20 +0100
      Re: [PATCH RESEND 22/27] tools/hv: Use include/uapi with  __EXPORTED_HEADERS__ Kamal Mostafa <kamal@canonical.com> - 2015-12-15 19:20 +0100
        [PATCH v2] tools/hv: Use include/uapi with __EXPORTED_HEADERS__ Kamal Mostafa <kamal@canonical.com> - 2015-12-15 19:30 +0100
          Re: [PATCH v2] tools/hv: Use include/uapi with __EXPORTED_HEADERS__ Greg KH <gregkh@linuxfoundation.org> - 2015-12-15 19:50 +0100
  [PATCH RESEND 25/27] Drivers: hv: vmbus: Force all channel messages to be delivered on CPU 0 "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 21/27] drivers:hv: Allow for MMIO claims that span ACPI _CRS records "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 24/27] drivers/hv: correct tsc page sequence invalid value "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 11/27] Drivers: hv: vss: run only on supported host versions "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 27/27] tools: hv: vss: fix the write()'s argument: error -> vss_msg "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 16/27] Drivers: hv: vmbus: serialize process_chn_event() and vmbus_close_internal() "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 18/27] Drivers: hv: vmbus: fix rescind-offer handling for device without a driver "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 19/27] Drivers: hv: vmbus: release relid on error in vmbus_process_offer() "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 23/27] Drivers: hv: vmbus: Fix a Host signaling bug "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:40 +0100
  [PATCH RESEND 17/27] Drivers: hv: vmbus: do sanity check of channel state in vmbus_close_internal() "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:50 +0100
  [PATCH RESEND 13/27] Drivers: hv: vmbus: Use uuid_le_cmp() for comparing GUIDs "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:50 +0100
  [PATCH RESEND 12/27] Drivers: hv: vmbus: Use uuid_le type consistently "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:50 +0100
  [PATCH RESEND 15/27] Drivers: hv: vmbus: Get rid of the unused irq variable "K. Y. Srinivasan" <kys@microsoft.com> - 2015-12-14 23:50 +0100

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