Revision 4e54dede38b45052a941bcf709f7d29f2e18174d authored by Michal Hocko on 27 February 2015, 23:51:46 UTC, committed by Linus Torvalds on 28 February 2015, 17:57:51 UTC
A memcg is considered low limited even when the current usage is equal to the low limit. This leads to interesting side effects e.g. groups/hierarchies with no memory accounted are considered protected and so the reclaim will emit MEMCG_LOW event when encountering them. Another and much bigger issue was reported by Joonsoo Kim. He has hit a NULL ptr dereference with the legacy cgroup API which even doesn't have low limit exposed. The limit is 0 by default but the initial check fails for memcg with 0 consumption and parent_mem_cgroup() would return NULL if use_hierarchy is 0 and so page_counter_read would try to dereference NULL. I suppose that the current implementation is just an overlook because the documentation in Documentation/cgroups/unified-hierarchy.txt says: "The memory.low boundary on the other hand is a top-down allocated reserve. A cgroup enjoys reclaim protection when it and all its ancestors are below their low boundaries" Fix the usage and the low limit comparision in mem_cgroup_low accordingly. Fixes: 241994ed8649 (mm: memcontrol: default hierarchy interface for memory) Reported-by: Joonsoo Kim <js1304@gmail.com> Signed-off-by: Michal Hocko <mhocko@suse.cz> 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>
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Kconfig
#
# For a description of the syntax of this configuration file,
# see Documentation/kbuild/kconfig-language.txt.
#
mainmenu "Linux/$ARCH $KERNELVERSION Kernel Configuration"
config SRCARCH
string
option env="SRCARCH"
source "arch/$SRCARCH/Kconfig"
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