linux-kernel - [PATCH 1/1] staging: hv: Fix race condition on IC channel initialization (modified)

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Message-ID: <1FB5E1D5CA062146B38059374562DF7266B8C4AC@TK5EX14MBXC128.redmond.corp.microsoft.com>
Date:	Wed, 26 May 2010 16:54:39 +0000
From:	Haiyang Zhang <haiyangz@...rosoft.com>
To:	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'devel@...verdev.osuosl.org'" <devel@...verdev.osuosl.org>,
	"'virtualization@...ts.osdl.org'" <virtualization@...ts.osdl.org>,
	"'gregkh@...e.de'" <gregkh@...e.de>
CC:	Hank Janssen <hjanssen@...rosoft.com>
Subject: [PATCH 1/1] staging: hv: Fix race condition on IC channel
 initialization (modified)

From: Haiyang Zhang <haiyangz@...rosoft.com>

Subject: [PATCH] staging: hv: Fix race condition on IC channel initialization
There is a possible race condition when hv_utils starts to load immediately
after hv_vmbus is loading - null pointer error could happen.
This patch added an event waiting to ensure all channels are ready before
vmbus_init() returns. So another module won't have any uninitialized channel.

Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
Signed-off-by: Hank Janssen <hjanssen@...rosoft.com>

---
 drivers/staging/hv/channel_mgmt.c  |   23 +++++++++++++----------
 drivers/staging/hv/vmbus_drv.c     |   10 ++++++++++
 drivers/staging/hv/vmbus_private.h |    1 +
 3 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/drivers/staging/hv/channel_mgmt.c b/drivers/staging/hv/channel_mgmt.c
index 3f53b4d..f99db1b 100644
--- a/drivers/staging/hv/channel_mgmt.c
+++ b/drivers/staging/hv/channel_mgmt.c
@@ -305,6 +305,7 @@ static void VmbusChannelProcessOffer(void *context)
 	int ret;
 	int cnt;
 	unsigned long flags;
+	static atomic_t ic_channel_initcnt = ATOMIC_INIT(0);
 
 	DPRINT_ENTER(VMBUS);
 
@@ -373,22 +374,24 @@ static void VmbusChannelProcessOffer(void *context)
 		 * can cleanup properly
 		 */
 		newChannel->State = CHANNEL_OPEN_STATE;
-		cnt = 0;
 
-		while (cnt != MAX_MSG_TYPES) {
+		/* Open IC channels */
+		for (cnt = 0; cnt < MAX_MSG_TYPES; cnt++) {
 			if (memcmp(&newChannel->OfferMsg.Offer.InterfaceType,
 				   &hv_cb_utils[cnt].data,
-				   sizeof(struct hv_guid)) == 0) {
+				   sizeof(struct hv_guid)) == 0 &&
+			    VmbusChannelOpen(newChannel, 2 * PAGE_SIZE,
+					     2 * PAGE_SIZE, NULL, 0,
+					     hv_cb_utils[cnt].callback,
+					     newChannel) == 0) {
+				hv_cb_utils[cnt].channel = newChannel;
+				mb();
 				DPRINT_INFO(VMBUS, "%s",
 					    hv_cb_utils[cnt].log_msg);
-
-				if (VmbusChannelOpen(newChannel, 2 * PAGE_SIZE,
-						    2 * PAGE_SIZE, NULL, 0,
-						    hv_cb_utils[cnt].callback,
-						    newChannel) == 0)
-					hv_cb_utils[cnt].channel = newChannel;
+				if (atomic_inc_return(&ic_channel_initcnt) ==
+				   MAX_MSG_TYPES)
+					osd_WaitEventSet(ic_channel_ready);
 			}
-			cnt++;
 		}
 	}
 	DPRINT_EXIT(VMBUS);
diff --git a/drivers/staging/hv/vmbus_drv.c b/drivers/staging/hv/vmbus_drv.c
index c21731a..3ae8981 100644
--- a/drivers/staging/hv/vmbus_drv.c
+++ b/drivers/staging/hv/vmbus_drv.c
@@ -989,6 +989,8 @@ static struct dmi_system_id __initdata microsoft_hv_dmi_table[] = {
 };
 MODULE_DEVICE_TABLE(dmi, microsoft_hv_dmi_table);
 
+struct osd_waitevent *ic_channel_ready;
+
 static int __init vmbus_init(void)
 {
 	int ret = 0;
@@ -1003,8 +1005,16 @@ static int __init vmbus_init(void)
 	if (!dmi_check_system(microsoft_hv_dmi_table))
 		return -ENODEV;
 
+	ic_channel_ready = osd_WaitEventCreate();
+	if (ic_channel_ready == NULL)
+		return -ENOMEM;
+
 	ret = vmbus_bus_init(VmbusInitialize);
 
+	/* Wait until all IC channels are initialized */
+	osd_WaitEventWait(ic_channel_ready);
+
+	kfree(ic_channel_ready);
 	DPRINT_EXIT(VMBUS_DRV);
 	return ret;
 }
diff --git a/drivers/staging/hv/vmbus_private.h b/drivers/staging/hv/vmbus_private.h
index 588c667..3fb8dad 100644
--- a/drivers/staging/hv/vmbus_private.h
+++ b/drivers/staging/hv/vmbus_private.h
@@ -130,5 +130,6 @@ int VmbusSetEvent(u32 childRelId);
 
 void VmbusOnEvents(void);
 
+extern struct osd_waitevent *ic_channel_ready;
 
 #endif /* _VMBUS_PRIVATE_H_ */
-- 
1.6.3.2


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