linux-kernel - [PATCH 6/9] ksm: mem cgroup charge swapin copy

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]

Date:	Tue, 24 Nov 2009 16:51:13 +0000 (GMT)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Izik Eidus <ieidus@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Chris Wright <chrisw@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 6/9] ksm: mem cgroup charge swapin copy

But ksm swapping does require one small change in mem cgroup handling.
When do_swap_page()'s call to ksm_might_need_to_copy() does indeed
substitute a duplicate page to accommodate a different anon_vma (or a
different index), that page escaped mem cgroup accounting, because of
the !PageSwapCache check in mem_cgroup_try_charge_swapin().

That was returning success without charging, on the assumption that
pte_same() would fail after, which is not the case here.  Originally I
proposed that success, so that an unshrinkable mem cgroup at its limit
would not fail unnecessarily; but that's a minor point, and there are
plenty of other places where we may fail an overallocation which might
later prove unnecessary.  So just go ahead and do what all the other
exceptions do: proceed to charge current mm.

Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
---

 mm/memcontrol.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- ksm5/mm/memcontrol.c	2009-11-14 10:17:02.000000000 +0000
+++ ksm6/mm/memcontrol.c	2009-11-22 20:40:37.000000000 +0000
@@ -1862,11 +1862,12 @@ int mem_cgroup_try_charge_swapin(struct
 		goto charge_cur_mm;
 	/*
 	 * A racing thread's fault, or swapoff, may have already updated
-	 * the pte, and even removed page from swap cache: return success
-	 * to go on to do_swap_page()'s pte_same() test, which should fail.
+	 * the pte, and even removed page from swap cache: in those cases
+	 * do_swap_page()'s pte_same() test will fail; but there's also a
+	 * KSM case which does need to charge the page.
 	 */
 	if (!PageSwapCache(page))
-		return 0;
+		goto charge_cur_mm;
 	mem = try_get_mem_cgroup_from_swapcache(page);
 	if (!mem)
 		goto charge_cur_mm;
--
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/