[PATCH 0/5] drivers: xen frontend devices should handle missed backend CLOSING

Subsystem maintainers, you can either pick up the relevant driver patch
or ack it to go via Konrad's Xen tree.

The series makes all the Xen frontend drivers handle the backend
transitioning to CLOSED without the frontend having previously seen
the backend in the CLOSING state.

Backends shouldn't do this but some do.  e.g., if the host is
XenServer and the toolstack decides to do a forced shutdown of a VBD,
then the blkfront may miss the CLOSING transition and the /dev/xvdX
device will not be destroyed which prevents it being reused.

I have seen systems that ended up in this state but it's not clear if
this was the actual cause.  However, I think in general it's a good
thing to thing to improve the handling of unexpected state
transitions.

David

From: David Vrabel <redacted>

Backend drivers shouldn't transistion to CLOSED unless the frontend is
CLOSED.  If a backend does transition to CLOSED too soon then the
frontend may not see the CLOSING state and will not properly shutdown.

So, treat an unexpected backend CLOSED state the same as CLOSING.

Signed-off-by: David Vrabel <redacted>
Acked-by: Konrad Rzeszutek Wilk <redacted>
---
Cc: linux-fbdev@vger.kernel.org
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
---
 drivers/video/xen-fbfront.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/drivers/video/xen-fbfront.c b/drivers/video/xen-fbfront.c
index b7f5173..917bb56 100644
--- a/drivers/video/xen-fbfront.c
+++ b/drivers/video/xen-fbfront.c

@@ -641,7 +641,6 @@ static void xenfb_backend_changed(struct xenbus_device *dev,
 	case XenbusStateReconfiguring:
 	case XenbusStateReconfigured:
 	case XenbusStateUnknown:
-	case XenbusStateClosed:
 		break;
 
 	case XenbusStateInitWait:

@@ -670,6 +669,10 @@ InitWait:
 		info->feature_resize = val;
 		break;
 
+	case XenbusStateClosed:
+		if (dev->state = XenbusStateClosed)
+			break;
+		/* Missed the backend's CLOSING state -- fallthrough */
 	case XenbusStateClosing:
 		xenbus_frontend_closed(dev);
 		break;

-- 
1.7.2.5

On Thu, Oct 18, 2012 at 11:03:37AM +0100, David Vrabel wrote:

From: David Vrabel <redacted>

Backend drivers shouldn't transistion to CLOSED unless the frontend is
CLOSED.  If a backend does transition to CLOSED too soon then the
frontend may not see the CLOSING state and will not properly shutdown.

So, treat an unexpected backend CLOSED state the same as CLOSING.

Signed-off-by: David Vrabel <redacted>
Acked-by: Konrad Rzeszutek Wilk <redacted>
---
Cc: linux-fbdev@vger.kernel.org
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>

Hey Florian,

Should I prep a git pull for you with this or would it be OK
if I just have your Ack to put this in my git pull for Linus?

Thanks!

Hi Konrad,

On 10/19/2012 01:00 PM, Konrad Rzeszutek Wilk wrote:

On Thu, Oct 18, 2012 at 11:03:37AM +0100, David Vrabel wrote:

quoted

From: David Vrabel <redacted>

Backend drivers shouldn't transistion to CLOSED unless the frontend is
CLOSED.  If a backend does transition to CLOSED too soon then the
frontend may not see the CLOSING state and will not properly shutdown.

So, treat an unexpected backend CLOSED state the same as CLOSING.

Signed-off-by: David Vrabel <redacted>
Acked-by: Konrad Rzeszutek Wilk <redacted>
---
Cc: linux-fbdev@vger.kernel.org
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>

Hey Florian,

Should I prep a git pull for you with this or would it be OK
if I just have your Ack to put this in my git pull for Linus?

Feel free to take it and add
Acked-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>


Best regards,

Florian Tobias Schandinat

Thanks!

quoted

---
 drivers/video/xen-fbfront.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/drivers/video/xen-fbfront.c b/drivers/video/xen-fbfront.c
index b7f5173..917bb56 100644
--- a/drivers/video/xen-fbfront.c
+++ b/drivers/video/xen-fbfront.c

@@ -641,7 +641,6 @@ static void xenfb_backend_changed(struct xenbus_device *dev,
 	case XenbusStateReconfiguring:
 	case XenbusStateReconfigured:
 	case XenbusStateUnknown:
-	case XenbusStateClosed:
 		break;
 
 	case XenbusStateInitWait:

@@ -670,6 +669,10 @@ InitWait:
 		info->feature_resize = val;
 		break;
 
+	case XenbusStateClosed:
+		if (dev->state = XenbusStateClosed)
+			break;
+		/* Missed the backend's CLOSING state -- fallthrough */
 	case XenbusStateClosing:
 		xenbus_frontend_closed(dev);
 		break;

-- 
1.7.2.5