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

[K. Y. Srinivasan]

From: Dexuan Cui <de...@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 <de...@microsoft.com>
Signed-off-by: K. Y. Srinivasan <k...@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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