4.9-stable review patch. If anyone has any objections, please let me know.
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From: Ross Lagerwall ross.lagerwall@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.lagerwall@citrix.com Reviewed-by: Boris Ostrovsky boris.ostrovsky@oracle.com Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/xen/grant-table.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/xen/grant-table.c +++ b/drivers/xen/grant-table.c @@ -327,7 +327,7 @@ static void gnttab_handle_deferred(unsig 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); @@ -383,7 +383,7 @@ void gnttab_end_foreign_access(grant_ref 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);