linux-kernel - [RFC PATCH v3 28/31] mm/page_alloc: in page_outside_zone

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1367539263-19999-29-git-send-email-cody@linux.vnet.ibm.com>
Date:	Thu,  2 May 2013 17:01:00 -0700
From:	Cody P Schafer <cody@...ux.vnet.ibm.com>
To:	Linux MM <linux-mm@...ck.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>,
	Simon Jeons <simon.jeons@...il.com>
Subject: [RFC PATCH v3 28/31] mm/page_alloc: in page_outside_zone_boundaries(), avoid premature decisions.

With some code that expands the zone boundaries, VM_BUG_ON(bad_range()) was being triggered.

Previously, page_outside_zone_boundaries() decided that once it detected
a page outside the boundaries, it was certainly outside even if the
seqlock indicated the data was invalid & needed to be reread. This
methodology _almost_ works because zones are only ever grown. However,
becase the zone span is stored as a start and a length, some expantions
momentarily appear as shifts to the left (when the zone_start_pfn is
assigned prior to zone_spanned_pages).

If we want to remove the seqlock around zone_start_pfn & zone
spanned_pages, always writing the spanned_pages first, issuing a memory
barrier, and then writing the new zone_start_pfn _may_ work. The concern
there is that we could be seen as shrinking the span when zone_start_pfn
is written (the entire span would shift to the left). As there will be
no pages in the exsess span that actually belong to the zone being
manipulated, I don't expect there to be issues.

Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>
---
 mm/page_alloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 879ab9d..3695ca5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -239,12 +239,13 @@ bool oom_killer_disabled __read_mostly;
 #ifdef CONFIG_DEBUG_VM
 static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
 {
-	int ret = 0;
+	int ret;
 	unsigned seq;
 	unsigned long pfn = page_to_pfn(page);
 	unsigned long sp, start_pfn;

 	do {
+		ret = 0;
 		seq = zone_span_seqbegin(zone);
 		start_pfn = zone->zone_start_pfn;
 		sp = zone->spanned_pages;
-- 
1.8.2.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/