Re: [patch] xenfb: fix xenfb suspend/resume race

Joe Jin
2010-12-31T00:57:31Z

On 12/31/10 00:40, Konrad Rzeszutek Wilk wrote:
> On Thu, Dec 30, 2010 at 08:56:16PM +0800, Joe Jin wrote:
>> Hi,
>
> Joe,
>
> Patch looks good, however..
>
> I am unclear from your description whether the patch fixes
> the problem (I would presume so). Or does it take a long time
> to hit this race?
>
Yes, more than 100 migrations. we hit this issue around 3 times.

I dumped vmcore when guest crashed, from vmcore everything
looked good, fb_info, xenfb_info and so on.

Checked the calltrace I suspected when guest resuming, the process kevent
scheduled and refresh xenfb. look like when call notify_remote_via_irq(), better
to confirm irq is valid?

Please review new patch.

Signed-off-by: Joe Jin <joe.jin@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Andrew Morton <akpm@linux-foundation.org>

---
video/xen-fbfront.c | 19 +++++++++++--------
xen/events.c | 2 ++
2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/video/xen-fbfront.c b/drivers/video/xen-fbfront.c
index dc72563..367fb1c 100644
--- a/drivers/video/xen-fbfront.c
+++ b/drivers/video/xen-fbfront.c
@@ -561,26 +561,24 @@ static void xenfb_init_shared_page(struct xenfb_info *info,
static int xenfb_connect_backend(struct xenbus_device *dev,
struct xenfb_info *info)
{
- int ret, evtchn;
+ int ret, evtchn, irq;
struct xenbus_transaction xbt;

ret = xenbus_alloc_evtchn(dev, &evtchn);
if (ret)
return ret;
- ret = bind_evtchn_to_irqhandler(evtchn, xenfb_event_handler,
+ irq = bind_evtchn_to_irqhandler(evtchn, xenfb_event_handler,
0, dev->devicetype, info);
- if (ret < 0) {
+ if (irq < 0) {
xenbus_free_evtchn(dev, evtchn);
xenbus_dev_fatal(dev, ret, "bind_evtchn_to_irqhandler");
- return ret;
+ return irq;
}
- info->irq = ret;
-
again:
ret = xenbus_transaction_start(&xbt);
if (ret) {
xenbus_dev_fatal(dev, ret, "starting transaction");
- return ret;
+ goto unbind_irq;
}
ret = xenbus_printf(xbt, dev->nodename, "page-ref", "%lu",
virt_to_mfn(info->page));
@@ -602,15 +600,20 @@ static int xenfb_connect_backend(struct xenbus_device *dev,
if (ret == -EAGAIN)
goto again;
xenbus_dev_fatal(dev, ret, "completing transaction");
- return ret;
+ goto unbind_irq;
}

xenbus_switch_state(dev, XenbusStateInitialised);
+ info->irq = irq;
return 0;

error_xenbus:
xenbus_transaction_end(xbt, 1);
xenbus_dev_fatal(dev, ret, "writing xenstore");
+ unbind_irq:
+ printk(KERN_ERR "xenfb_connect_backend failed!\n");
+ unbind_from_irqhandler(irq, info);
+ xenbus_free_evtchn(dev, evtchn);
return ret;
}

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index ac7b42f..4cfb5e2 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -175,6 +175,8 @@ static struct irq_info *info_for_irq(unsigned irq)

static unsigned int evtchn_from_irq(unsigned irq)
{
+ if (unlikely(irq < 0 || irq >= nr_irqs))
+ return 0;
return info_for_irq(irq)->evtchn;
}