On Sat 31-08-13 17:06:42, Greg Thelen wrote: > 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@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxx> I guess this qualifies to the stable tree. Thanks! > --- > mm/memcontrol.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 0878ff7..aa44621 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5616,7 +5616,13 @@ 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) > -- > 1.8.4 > -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>