This is a note to let you know that I've just added the patch titled
mm, page_alloc: fix fast-path race with cpuset update or removal
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-page_alloc-fix-fast-path-race-with-cpuset-update-or-removal.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 16096c25bf0ca5d87e4fa6ec6108ba53feead212 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@xxxxxxx>
Date: Tue, 24 Jan 2017 15:18:35 -0800
Subject: mm, page_alloc: fix fast-path race with cpuset update or removal
From: Vlastimil Babka <vbabka@xxxxxxx>
commit 16096c25bf0ca5d87e4fa6ec6108ba53feead212 upstream.
Ganapatrao Kulkarni reported that the LTP test cpuset01 in stress mode
triggers OOM killer in few seconds, despite lots of free memory. The
test attempts to repeatedly fault in memory in one process in a cpuset,
while changing allowed nodes of the cpuset between 0 and 1 in another
process.
One possible cause is that in the fast path we find the preferred
zoneref according to current mems_allowed, so that it points to the
middle of the zonelist, skipping e.g. zones of node 1 completely. If
the mems_allowed is updated to contain only node 1, we never reach it in
the zonelist, and trigger OOM before checking the cpuset_mems_cookie.
This patch fixes the particular case by redoing the preferred zoneref
search if we switch back to the original nodemask. The condition is
also slightly changed so that when the last non-root cpuset is removed,
we don't miss it.
Note that this is not a full fix, and more patches will follow.
Link: http://lkml.kernel.org/r/20170120103843.24587-3-vbabka@xxxxxxx
Fixes: 682a3385e773 ("mm, page_alloc: inline the fast path of the zonelist iterator")
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reported-by: Ganapatrao Kulkarni <gpkulkarni@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3783,9 +3783,17 @@ retry_cpuset:
/*
* Restore the original nodemask if it was potentially replaced with
* &cpuset_current_mems_allowed to optimize the fast-path attempt.
+ * Also recalculate the starting point for the zonelist iterator or
+ * we could end up iterating over non-eligible zones endlessly.
*/
- if (cpusets_enabled())
+ if (unlikely(ac.nodemask != nodemask)) {
ac.nodemask = nodemask;
+ ac.preferred_zoneref = first_zones_zonelist(ac.zonelist,
+ ac.high_zoneidx, ac.nodemask);
+ if (!ac.preferred_zoneref->zone)
+ goto no_zone;
+ }
+
page = __alloc_pages_slowpath(alloc_mask, order, &ac);
no_zone:
Patches currently in stable-queue which might be from vbabka@xxxxxxx are
queue-4.9/mm-page_alloc-fix-fast-path-race-with-cpuset-update-or-removal.patch
queue-4.9/mm-page_alloc-fix-check-for-null-preferred_zone.patch
queue-4.9/mm-mempolicy.c-do-not-put-mempolicy-before-using-its-nodemask.patch
queue-4.9/mm-page_alloc-fix-premature-oom-when-racing-with-cpuset-mems-update.patch
queue-4.9/mm-page_alloc-move-cpuset-seqcount-checking-to-slowpath.patch
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