Re: [PATCH] reset PV devices in crash kernel

[Olaf Hering <olaf@aepfle.de>]

On Fri, Feb 04, Olaf Hering wrote:


Ping?
Can this and the reset_devices patch be applied to the 2.6.18 tree?

Olaf

> 
> After triggering a crash dump in a HVM guest, the PV backend drivers
> will remain in connected state.  When the kdump kernel starts the PV
> drivers will skip such devices.  As a result, no root device is found
> and the vmcore cant be saved.
> 
> With this change all frontend devices with state XenbusStateConnected
> will be reset by changing the state file to Closing/Closed/Initializing.
> This will trigger a disconnect in the backend drivers. Now the frontend
> drivers will find the backend drivers in state Initwait and can connect.
> 
> Signed-off-by: Olaf Hering <olaf@aepfle.de>
> 
> ---
>  drivers/xen/xenbus/xenbus_comms.c |    4 +
>  drivers/xen/xenbus/xenbus_probe.c |   96 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 99 insertions(+), 1 deletion(-)
> 
> --- linux-2.6.18-xen.hg.orig/drivers/xen/xenbus/xenbus_comms.c
> +++ linux-2.6.18-xen.hg/drivers/xen/xenbus/xenbus_comms.c
> @@ -234,7 +234,9 @@ int xb_init_comms(void)
>  		printk(KERN_WARNING "XENBUS response ring is not quiescent "
>  		       "(%08x:%08x): fixing up\n",
>  		       intf->rsp_cons, intf->rsp_prod);
> -		intf->rsp_cons = intf->rsp_prod;
> +		/* breaks kdump */
> +		if (!reset_devices)
> +			intf->rsp_cons = intf->rsp_prod;
>  	}
>  
>  	if (xenbus_irq)
> --- linux-2.6.18-xen.hg.orig/drivers/xen/xenbus/xenbus_probe.c
> +++ linux-2.6.18-xen.hg/drivers/xen/xenbus/xenbus_probe.c
> @@ -854,11 +854,107 @@ void unregister_xenstore_notifier(struct
>  }
>  EXPORT_SYMBOL_GPL(unregister_xenstore_notifier);
>  
> +#ifdef CONFIG_CRASH_DUMP
> +static DECLARE_WAIT_QUEUE_HEAD(be_state_wq);
> +static int be_state;
> +
> +static void xenbus_reset_state_changed(struct xenbus_watch *w, const char **v, unsigned int l)
> +{
> +	xenbus_scanf(XBT_NIL, v[XS_WATCH_PATH], "", "%i", &be_state);
> +	printk(KERN_INFO "XENBUS: %s %s", v[XS_WATCH_PATH], xenbus_strstate(be_state));
> +	wake_up(&be_state_wq);
> +}
> +
> +static int xenbus_reset_check_final(int *st)
> +{
> +	return *st == XenbusStateInitialising || *st == XenbusStateInitWait;
> +}
> +
> +static void xenbus_reset_frontend_state(char *backend, char *frontend)
> +{
> +	struct xenbus_watch watch;
> +
> +	memset(&watch, 0, sizeof(watch));
> +	watch.node = kasprintf(GFP_NOIO | __GFP_HIGH, "%s/state", backend);
> +	if (!watch.node)
> +		return;
> +
> +	watch.callback = xenbus_reset_state_changed;
> +	be_state = XenbusStateUnknown;
> +
> +	printk(KERN_INFO "triggering reconnect on %s", backend);
> +	register_xenbus_watch(&watch);
> +
> +	xenbus_printf(XBT_NIL, frontend, "state", "%d", XenbusStateClosing);
> +	wait_event_interruptible(be_state_wq, be_state == XenbusStateClosing);
> +
> +	xenbus_printf(XBT_NIL, frontend, "state", "%d", XenbusStateClosed);
> +	wait_event_interruptible(be_state_wq, be_state == XenbusStateClosed);
> +
> +	xenbus_printf(XBT_NIL, frontend, "state", "%d", XenbusStateInitialising);
> +	wait_event_interruptible(be_state_wq, xenbus_reset_check_final(&be_state));
> +
> +	unregister_xenbus_watch(&watch);
> +	printk(KERN_INFO "reconnect done on %s", backend);
> +	kfree(watch.node);
> +}
> +
> +static void xenbus_reset_check_state(char *frontend)
> +{
> +	int state, err;
> +	char *backend;
> +
> +	err = xenbus_scanf(XBT_NIL, frontend, "state", "%i", &state);
> +	/* frontend connected? */
> +	if (err == 1 && state == XenbusStateConnected) {
> +		backend = xenbus_read(XBT_NIL, frontend, "backend", NULL);
> +		if (!backend || IS_ERR(backend))
> +			return;
> +		err = xenbus_scanf(XBT_NIL, backend, "state", "%i", &state);
> +		/* backend connected? */
> +		if (err == 1 && state == XenbusStateConnected)
> +			xenbus_reset_frontend_state(backend, frontend);
> +		kfree(backend);
> +	}
> +}
> +
> +static void xenbus_reset_state(void)
> +{
> +	char *frontend;
> +	char **devclass, **dev;
> +	int devclass_n, dev_n;
> +	int i, j;
> +
> +	devclass = xenbus_directory(XBT_NIL, "device", "", &devclass_n);
> +	if (IS_ERR(devclass))
> +		return;
> +
> +	for (i = 0; i < devclass_n; i++) {
> +		dev = xenbus_directory(XBT_NIL, "device", devclass[i], &dev_n);
> +		if (IS_ERR(dev))
> +			continue;
> +		for (j = 0; j < dev_n; j++) {
> +			frontend = kasprintf(GFP_NOIO|__GFP_HIGH, "device/%s/%s", devclass[i], dev[j]);
> +			if (!frontend)
> +				continue;
> +			xenbus_reset_check_state(frontend);
> +			kfree(frontend);
> +		}
> +		kfree(dev);
> +	}
> +	kfree(devclass);
> +}
> +#endif
>  
>  void xenbus_probe(void *unused)
>  {
>  	BUG_ON(!is_xenstored_ready());
>  
> +#ifdef CONFIG_CRASH_DUMP
> +	/* reset devices in XenbusStateConnected state */
> +	if (!is_initial_xendomain() && reset_devices)
> +		xenbus_reset_state();
> +#endif
>  	/* Enumerate devices in xenstore and watch for changes. */
>  	xenbus_probe_devices(&xenbus_frontend);
>  	register_xenbus_watch(&fe_watch);