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Haiyang Zhang

2010-May-21 19:58 UTC

[PATCH 1/1] staging: hv: Fix race condition on IC channel initialization

From: Haiyang Zhang <haiyangz at microsoft.com>

Subject: 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 atomic counter 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 at microsoft.com>
Signed-off-by: Hank Janssen <hjanssen at microsoft.com>

---
 drivers/staging/hv/channel_mgmt.c |   25 ++++++++++++++-----------
 drivers/staging/hv/hv_utils.c     |    7 ++++---
 drivers/staging/hv/utils.h        |    5 +++++
 drivers/staging/hv/vmbus_drv.c    |    5 +++++
 4 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/drivers/staging/hv/channel_mgmt.c
b/drivers/staging/hv/channel_mgmt.c
index 3f53b4d..68dfa0f 100644
--- a/drivers/staging/hv/channel_mgmt.c
+++ b/drivers/staging/hv/channel_mgmt.c
@@ -33,7 +33,6 @@ struct vmbus_channel_message_table_entry {
 	void (*messageHandler)(struct vmbus_channel_message_header *msg);
 };
 
-#define MAX_MSG_TYPES                    3
 #define MAX_NUM_DEVICE_CLASSES_SUPPORTED 7
 
 static const struct hv_guid
@@ -233,6 +232,10 @@ struct hyperv_service_callback hv_cb_utils[MAX_MSG_TYPES] =
{
 };
 EXPORT_SYMBOL(hv_cb_utils);
 
+/* Counter of IC channels initialized */
+atomic_t hv_utils_initcnt = ATOMIC_INIT(0);
+
+
 /*
  * AllocVmbusChannel - Allocate and initialize a vmbus channel object
  */
@@ -373,22 +376,22 @@ 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;
+				atomic_inc(&hv_utils_initcnt);
 			}
-			cnt++;
 		}
 	}
 	DPRINT_EXIT(VMBUS);
diff --git a/drivers/staging/hv/hv_utils.c b/drivers/staging/hv/hv_utils.c
index 8a49aaf..22f6f4a 100644
--- a/drivers/staging/hv/hv_utils.c
+++ b/drivers/staging/hv/hv_utils.c
@@ -253,7 +253,7 @@ static void heartbeat_onchannelcallback(void *context)
 
 static int __init init_hyperv_utils(void)
 {
-	printk(KERN_INFO "Registering HyperV Utility Driver\n");
+	printk(KERN_INFO "Registering HyperV Utility Driver...\n");
 
 	hv_cb_utils[HV_SHUTDOWN_MSG].channel->OnChannelCallback  	
&shutdown_onchannelcallback;
@@ -267,13 +267,12 @@ static int __init init_hyperv_utils(void)
 		&heartbeat_onchannelcallback;
 	hv_cb_utils[HV_HEARTBEAT_MSG].callback = &heartbeat_onchannelcallback;
 
+	printk(KERN_INFO "Registered HyperV Utility Driver.\n");
 	return 0;
 }
 
 static void exit_hyperv_utils(void)
 {
-	printk(KERN_INFO "De-Registered HyperV Utility Driver\n");
-
 	hv_cb_utils[HV_SHUTDOWN_MSG].channel->OnChannelCallback  	
&chn_cb_negotiate;
 	hv_cb_utils[HV_SHUTDOWN_MSG].callback = &chn_cb_negotiate;
@@ -285,6 +284,8 @@ static void exit_hyperv_utils(void)
 	hv_cb_utils[HV_HEARTBEAT_MSG].channel->OnChannelCallback  	
&chn_cb_negotiate;
 	hv_cb_utils[HV_HEARTBEAT_MSG].callback = &chn_cb_negotiate;
+
+	printk(KERN_INFO "De-Registered HyperV Utility Driver.\n");
 }
 
 module_init(init_hyperv_utils);
diff --git a/drivers/staging/hv/utils.h b/drivers/staging/hv/utils.h
index 7c07499..3291ab4 100644
--- a/drivers/staging/hv/utils.h
+++ b/drivers/staging/hv/utils.h
@@ -98,6 +98,10 @@ struct ictimesync_data{
 	u8 flags;
 } __attribute__((packed));
 
+
+/* Number of IC types supported */
+#define MAX_MSG_TYPES	3
+
 /* Index for each IC struct in array hv_cb_utils[] */
 #define HV_SHUTDOWN_MSG		0
 #define HV_TIMESYNC_MSG		1
@@ -115,5 +119,6 @@ extern void prep_negotiate_resp(struct icmsg_hdr *,
 				struct icmsg_negotiate *, u8 *);
 extern void chn_cb_negotiate(void *);
 extern struct hyperv_service_callback hv_cb_utils[];
+extern atomic_t hv_utils_initcnt;
 
 #endif /* __HV_UTILS_H_ */
diff --git a/drivers/staging/hv/vmbus_drv.c b/drivers/staging/hv/vmbus_drv.c
index c21731a..160ee92 100644
--- a/drivers/staging/hv/vmbus_drv.c
+++ b/drivers/staging/hv/vmbus_drv.c
@@ -31,6 +31,7 @@
 #include "osd.h"
 #include "logging.h"
 #include "vmbus.h"
+#include "utils.h"
 
 
 /* FIXME! We need to do this dynamically for PIC and APIC system */
@@ -1005,6 +1006,10 @@ static int __init vmbus_init(void)
 
 	ret = vmbus_bus_init(VmbusInitialize);
 
+	/* Wait until all IC channels are initialized */
+	while (atomic_read(&hv_utils_initcnt) < MAX_MSG_TYPES)
+		msleep(100);
+
 	DPRINT_EXIT(VMBUS_DRV);
 	return ret;
 }
-- 
1.6.3.2

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Greg KH

2010-May-21 20:12 UTC

head link

[PATCH 1/1] staging: hv: Fix race condition on IC channel initialization

On Fri, May 21, 2010 at 07:58:26PM +0000, Haiyang Zhang
wrote:> From: Haiyang Zhang <haiyangz at microsoft.com>
> 
> Subject: 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 atomic counter to ensure all channels are ready before
> vmbus_init() returns. So another module won't have any uninitialized
channel.
Better, but not quite ready...
> +/* Counter of IC channels initialized */
> +atomic_t hv_utils_initcnt = ATOMIC_INIT(0);
This doesn't need to be an atomic variable, does it really?

Why not have a simple bool variable "vmbus_initialized" or something.
It starts out as false, and then turns true when you are up and ready.
Then provide a function that tests it:
	bool hv_vmbus_ready(void)
	{
		return vmbus_initialized
	}
	EXPORT_SYMBOL_GPL(hv_vmbus_ready);
>  /*
>   * AllocVmbusChannel - Allocate and initialize a vmbus channel object
>   */
> @@ -373,22 +376,22 @@ 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;
> +				atomic_inc(&hv_utils_initcnt);
>  			}
Then set the vmbus_initialized to be true right here.

This way, no one needs to know about what the internal number of
messages are, or any other internal mess that would require the bus to
be up and running properly.
> --- a/drivers/staging/hv/hv_utils.c
> +++ b/drivers/staging/hv/hv_utils.c
> @@ -253,7 +253,7 @@ static void heartbeat_onchannelcallback(void *context)
>  
>  static int __init init_hyperv_utils(void)
>  {
> -	printk(KERN_INFO "Registering HyperV Utility Driver\n");
> +	printk(KERN_INFO "Registering HyperV Utility Driver...\n");
>  
>  	hv_cb_utils[HV_SHUTDOWN_MSG].channel->OnChannelCallback >  	
&shutdown_onchannelcallback;
> @@ -267,13 +267,12 @@ static int __init init_hyperv_utils(void)
>  		&heartbeat_onchannelcallback;
>  	hv_cb_utils[HV_HEARTBEAT_MSG].callback =
&heartbeat_onchannelcallback;
>  
> +	printk(KERN_INFO "Registered HyperV Utility Driver.\n");
Just do one printk, if any at all here.  You really don't need it, it
just clutters up the syslog.  Especially given your code here, it's not
going to ever be a long time between those two messages :)
>  	return 0;
>  }
>  
>  static void exit_hyperv_utils(void)
>  {
> -	printk(KERN_INFO "De-Registered HyperV Utility Driver\n");
> -
>  	hv_cb_utils[HV_SHUTDOWN_MSG].channel->OnChannelCallback >  	
&chn_cb_negotiate;
>  	hv_cb_utils[HV_SHUTDOWN_MSG].callback = &chn_cb_negotiate;
> @@ -285,6 +284,8 @@ static void exit_hyperv_utils(void)
>  	hv_cb_utils[HV_HEARTBEAT_MSG].channel->OnChannelCallback >  	
&chn_cb_negotiate;
>  	hv_cb_utils[HV_HEARTBEAT_MSG].callback = &chn_cb_negotiate;
> +
> +	printk(KERN_INFO "De-Registered HyperV Utility Driver.\n");
Again, just drop the thing entirely.
>  }
>  
>  module_init(init_hyperv_utils);
> diff --git a/drivers/staging/hv/utils.h b/drivers/staging/hv/utils.h
> index 7c07499..3291ab4 100644
> --- a/drivers/staging/hv/utils.h
> +++ b/drivers/staging/hv/utils.h
> @@ -98,6 +98,10 @@ struct ictimesync_data{
>  	u8 flags;
>  } __attribute__((packed));
>  
> +
> +/* Number of IC types supported */
> +#define MAX_MSG_TYPES	3
Now you can keep this #define private.
> --- a/drivers/staging/hv/vmbus_drv.c
> +++ b/drivers/staging/hv/vmbus_drv.c
> @@ -31,6 +31,7 @@
>  #include "osd.h"
>  #include "logging.h"
>  #include "vmbus.h"
> +#include "utils.h"
>  
>  
>  /* FIXME! We need to do this dynamically for PIC and APIC system */
> @@ -1005,6 +1006,10 @@ static int __init vmbus_init(void)
>  
>  	ret = vmbus_bus_init(VmbusInitialize);
>  
> +	/* Wait until all IC channels are initialized */
> +	while (atomic_read(&hv_utils_initcnt) < MAX_MSG_TYPES)
> +		msleep(100);
this turns into a simple function call, again, never needing to know
about message types or any other mess.

Sound good?

thanks,

greg k-h

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