linux-kernel - Re: [PATCH v2 -mm] memcg: prevent from OOM with too many dirty pages

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: <alpine.LSU.2.00.1207112012020.3727@eggly.anvils>
Date:	Wed, 11 Jul 2012 20:13:40 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujtisu.com>,
	Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Ying Han <yinghan@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [PATCH v2 -mm] memcg: prevent from OOM with too many dirty
 pages

On Wed, 11 Jul 2012, Andrew Morton wrote:
> On Wed, 11 Jul 2012 18:57:43 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:
> 
> > --- 3.5-rc6-mm1/mm/vmscan.c	2012-07-11 14:42:13.668335884 -0700
> > +++ linux/mm/vmscan.c	2012-07-11 16:01:20.712814127 -0700
> > @@ -726,7 +726,8 @@ static unsigned long shrink_page_list(st
> >  			 * writeback from reclaim and there is nothing else to
> >  			 * reclaim.
> >  			 */
> > -			if (!global_reclaim(sc) && PageReclaim(page))
> > +			if (!global_reclaim(sc) && PageReclaim(page) &&
> > +					may_enter_fs)
> >  				wait_on_page_writeback(page);
> >  			else {
> >  				nr_writeback++;
> 
> um, that may_enter_fs test got removed because nobody knew why it was
> there.  Nobody knew why it was there because it was undocumented.  Do
> you see where I'm going with this?

I was hoping you might do that bit ;)  Here's my display of ignorance:

--- 3.5-rc6-mm1/mm/vmscan.c	2012-07-11 14:42:13.668335884 -0700
+++ linux/mm/vmscan.c	2012-07-11 20:09:33.182829986 -0700
@@ -725,8 +725,15 @@ static unsigned long shrink_page_list(st
 			 * could easily OOM just because too many pages are in
 			 * writeback from reclaim and there is nothing else to
 			 * reclaim.
+			 *
+			 * Check may_enter_fs, certainly because a loop driver
+			 * thread might enter reclaim, and deadlock if it waits
+			 * on a page for which it is needed to do the write
+			 * (loop masks off __GFP_IO|__GFP_FS for this reason);
+			 * but more thought would probably show more reasons.
 			 */
-			if (!global_reclaim(sc) && PageReclaim(page))
+			if (!global_reclaim(sc) && PageReclaim(page) &&
+					may_enter_fs)
 				wait_on_page_writeback(page);
 			else {
 				nr_writeback++;
--
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/