| From | Luis Henriques <> | Subject | [PATCH 093/104] memcg: fix multiple large threshold notifications | Date | Mon, 30 Sep 2013 11:11:10 +0100 |
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3.5.7.22 -stable review patch. If anyone has any objections, please let me know.
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From: Greg Thelen <gthelen@google.com>
commit 2bff24a3707093c435ab3241c47dcdb5f16e432b upstream.
A memory cgroup with (1) multiple threshold notifications and (2) at least one threshold >=2G was not reliable. Specifically the notifications would either not fire or would not fire in the proper order.
The __mem_cgroup_threshold() signaling logic depends on keeping 64 bit thresholds in sorted order. mem_cgroup_usage_register_event() sorts them with compare_thresholds(), which returns the difference of two 64 bit thresholds as an int. If the difference is positive but has bit[31] set, then sort() treats the difference as negative and breaks sort order.
This fix compares the two arbitrary 64 bit thresholds returning the classic -1, 0, 1 result.
The test below sets two notifications (at 0x1000 and 0x81001000): cd /sys/fs/cgroup/memory mkdir x for x in 4096 2164264960; do cgroup_event_listener x/memory.usage_in_bytes $x | sed "s/^/$x listener:/" & done echo $$ > x/cgroup.procs anon_leaker 500M
v3.11-rc7 fails to signal the 4096 event listener: Leaking... Done leaking pages.
Patched v3.11-rc7 properly notifies: Leaking... 4096 listener:2013:8:31:14:13:36 Done leaking pages.
The fixed bug is old. It appears to date back to the introduction of memcg threshold notifications in v2.6.34-rc1-116-g2e72b6347c94 "memcg: implement memory thresholds"
Signed-off-by: Greg Thelen <gthelen@google.com> Acked-by: Michal Hocko <mhocko@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- mm/memcontrol.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 08bcbd8..226b63e 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4298,7 +4298,13 @@ static int compare_thresholds(const void *a, const void *b) const struct mem_cgroup_threshold *_a = a; const struct mem_cgroup_threshold *_b = b; - return _a->threshold - _b->threshold; + if (_a->threshold > _b->threshold) + return 1; + + if (_a->threshold < _b->threshold) + return -1; + + return 0; } static int mem_cgroup_oom_notify_cb(struct mem_cgroup *memcg) -- 1.8.3.2
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