[PATCH] Input: xen-kbdfront - free grant table entry in xenkbd_disconnect_backend

[PATCH] Input: xen-kbdfront - free grant table entry in xenkbd_disconnect_backend

[hansechang]

From: Chang Huaixin <huaixin.chx@alibaba-inc.com>

xenkbd_disconnect_backend doesn't free grant table entry.
This bug affects live migration.

xenkbd_disconnect_backend uses gnttab_end_foreign_access_ref
to handle grant table entry which doesn't really free an entry.

Thus every time we do xenkbd_resume, grant table entry increses
by one. As an grant table entry occupies 8 bytes, an grant table
page has at most 512 entries. Every 512 times we do xenkdb_resume,
grant table pages increses by one.

After around 3500 times of live migration, grant table pages
will increase by 7, causing too many pages to populate and hitting
max_pages limit when assigning pages.Thus assign_pages will fail,
so will live migration.

Signed-off-by: Chang Huaixin <huaixin.chx@alibaba-inc.com>
---
 drivers/input/misc/xen-kbdfront.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/input/misc/xen-kbdfront.c b/drivers/input/misc/xen-kbdfront.c
index fbfdc10..e2ecfc6 100644
--- a/drivers/input/misc/xen-kbdfront.c
+++ b/drivers/input/misc/xen-kbdfront.c
@@ -285,7 +285,7 @@ static int xenkbd_connect_backend(struct xenbus_device *dev,
  error_evtchan:
 	xenbus_free_evtchn(dev, evtchn);
  error_grant:
-	gnttab_end_foreign_access_ref(info->gref, 0);
+	gnttab_end_foreign_access(info->gref, 0, 0UL);
 	info->gref = -1;
 	return ret;
 }
@@ -296,7 +296,7 @@ static void xenkbd_disconnect_backend(struct xenkbd_info *info)
 		unbind_from_irqhandler(info->irq, info);
 	info->irq = -1;
 	if (info->gref >= 0)
-		gnttab_end_foreign_access_ref(info->gref, 0);
+		gnttab_end_foreign_access(info->gref, 0, 0UL);
 	info->gref = -1;
 }
 
-- 
1.9.1

Re: [Xen-devel] [PATCH] Input: xen-kbdfront - free grant table entry in xenkbd_disconnect_backend

[David Vrabel]

On 16/10/14 02:46, hansechang@gmail.com wrote:
> From: Chang Huaixin <huaixin.chx@alibaba-inc.com>
> 
> xenkbd_disconnect_backend doesn't free grant table entry.
> This bug affects live migration.
> 
> xenkbd_disconnect_backend uses gnttab_end_foreign_access_ref
> to handle grant table entry which doesn't really free an entry.
> 
> Thus every time we do xenkbd_resume, grant table entry increses
> by one. As an grant table entry occupies 8 bytes, an grant table
> page has at most 512 entries. Every 512 times we do xenkdb_resume,
> grant table pages increses by one.
> 
> After around 3500 times of live migration, grant table pages
> will increase by 7, causing too many pages to populate and hitting
> max_pages limit when assigning pages.Thus assign_pages will fail,
> so will live migration.

Acked-by: David Vrabel <david.vrabel@citrix.com>

This need to be send to the input subsystem maintainers.

David

Re: [Xen-devel] [PATCH] Input: xen-kbdfront - free grant table entry in xenkbd_disconnect_backend

[Dmitry Torokhov]

On Thu, Oct 16, 2014 at 05:01:09PM +0100, David Vrabel wrote:
> On 16/10/14 02:46, hansechang@gmail.com wrote:
> > From: Chang Huaixin <huaixin.chx@alibaba-inc.com>
> > 
> > xenkbd_disconnect_backend doesn't free grant table entry.
> > This bug affects live migration.
> > 
> > xenkbd_disconnect_backend uses gnttab_end_foreign_access_ref
> > to handle grant table entry which doesn't really free an entry.
> > 
> > Thus every time we do xenkbd_resume, grant table entry increses
> > by one. As an grant table entry occupies 8 bytes, an grant table
> > page has at most 512 entries. Every 512 times we do xenkdb_resume,
> > grant table pages increses by one.
> > 
> > After around 3500 times of live migration, grant table pages
> > will increase by 7, causing too many pages to populate and hitting
> > max_pages limit when assigning pages.Thus assign_pages will fail,
> > so will live migration.
> 
> Acked-by: David Vrabel <david.vrabel@citrix.com>
> 
> This need to be send to the input subsystem maintainers.

Applied, thank you.

-- 
Dmitry