Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932803AbeAKJgv (ORCPT + 1 other); Thu, 11 Jan 2018 04:36:51 -0500 Received: from smtp.citrix.com ([66.165.176.89]:65207 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754657AbeAKJgq (ORCPT ); Thu, 11 Jan 2018 04:36:46 -0500 X-IronPort-AV: E=Sophos;i="5.46,343,1511827200"; d="scan'208";a="457830528" From: Ross Lagerwall To: CC: Ross Lagerwall , Boris Ostrovsky , Juergen Gross , Subject: [PATCH 1/2] xen/grant-table: Use put_page instead of free_page Date: Thu, 11 Jan 2018 09:36:37 +0000 Message-ID: <20180111093638.28937-2-ross.lagerwall@citrix.com> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20180111093638.28937-1-ross.lagerwall@citrix.com> References: <20180111093638.28937-1-ross.lagerwall@citrix.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 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 --- 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 f45114f..27be107 100644 --- a/drivers/xen/grant-table.c +++ b/drivers/xen/grant-table.c @@ -382,7 +382,7 @@ static void gnttab_handle_deferred(struct timer_list *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); @@ -438,7 +438,7 @@ 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); -- 2.9.5