From: Ross Lagerwall <ross.lagerw...@citrix.com>

[ Upstream commit 3ac7292a25db1c607a50752055a18aba32ac2176 ]

The page given to gnttab_end_foreign_access() to free could be a
compound page so use put_page() instead of free_page() since it can
handle both compound and single pages correctly.

This bug was discovered when migrating a Xen VM with several VIFs and
CONFIG_DEBUG_VM enabled. It hits a BUG usually after fewer than 10
iterations. All netfront devices disconnect from the backend during a
suspend/resume and this will call gnttab_end_foreign_access() if a
netfront queue has an outstanding skb. The mismatch between calling
get_page() and free_page() on a compound page causes a reference
counting error which is detected when DEBUG_VM is enabled.

Signed-off-by: Ross Lagerwall <ross.lagerw...@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrov...@oracle.com>
Signed-off-by: Juergen Gross <jgr...@suse.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
---
 drivers/xen/grant-table.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index c49f79ed58c5..4b7ce442d8e5 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -328,7 +328,7 @@ static void gnttab_handle_deferred(unsigned long unused)
                        if (entry->page) {
                                pr_debug("freeing g.e. %#x (pfn %#lx)\n",
                                         entry->ref, page_to_pfn(entry->page));
-                               __free_page(entry->page);
+                               put_page(entry->page);
                        } else
                                pr_info("freeing g.e. %#x\n", entry->ref);
                        kfree(entry);
@@ -384,7 +384,7 @@ void gnttab_end_foreign_access(grant_ref_t ref, int 
readonly,
        if (gnttab_end_foreign_access_ref(ref, readonly)) {
                put_free_entry(ref);
                if (page != 0)
-                       free_page(page);
+                       put_page(virt_to_page(page));
        } else
                gnttab_add_deferred(ref, readonly,
                                    page ? virt_to_page(page) : NULL);
-- 
2.15.1

Reply via email to