Subject: + memcg-fix-endless-loop-caused-by-mem_cgroup_iter.patch added to -mm tree
To: mhocko@xxxxxxx,gthelen@xxxxxxxxxx,hannes@xxxxxxxxxxx,hughd@xxxxxxxxxx,stable@xxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Tue, 21 Jan 2014 11:41:21 -0800
The patch titled
Subject: memcg: fix endless loop caused by mem_cgroup_iter
has been added to the -mm tree. Its filename is
memcg-fix-endless-loop-caused-by-mem_cgroup_iter.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/memcg-fix-endless-loop-caused-by-mem_cgroup_iter.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/memcg-fix-endless-loop-caused-by-mem_cgroup_iter.patch
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------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxx>
Subject: memcg: fix endless loop caused by mem_cgroup_iter
Hugh has reported an endless loop when the hardlimit reclaim sees the same
group all the time. This might happen when the reclaim races with the
memcg removal.
shrink_zone
[rmdir root]
mem_cgroup_iter(root, NULL, reclaim)
// prev = NULL
rcu_read_lock()
mem_cgroup_iter_load
last_visited = iter->last_visited // gets root || NULL
css_tryget(last_visited) // failed
last_visited = NULL [1]
memcg = root = __mem_cgroup_iter_next(root, NULL)
mem_cgroup_iter_update
iter->last_visited = root;
reclaim->generation = iter->generation
mem_cgroup_iter(root, root, reclaim)
// prev = root
rcu_read_lock
mem_cgroup_iter_load
last_visited = iter->last_visited // gets root
css_tryget(last_visited) // failed
[1]
The issue seemed to be introduced by 5f5781619718 ("memcg: relax memcg
iter caching") which has replaced unconditional css_get/css_put by
css_tryget/css_put for the cached iterator.
This patch fixes the issue by skipping css_tryget on the root of the tree
walk in mem_cgroup_iter_load and symmetrically doesn't release it in
mem_cgroup_iter_update.
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [3.10+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff -puN mm/memcontrol.c~memcg-fix-endless-loop-caused-by-mem_cgroup_iter mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-fix-endless-loop-caused-by-mem_cgroup_iter
+++ a/mm/memcontrol.c
@@ -1117,7 +1117,15 @@ mem_cgroup_iter_load(struct mem_cgroup_r
if (iter->last_dead_count == *sequence) {
smp_rmb();
position = iter->last_visited;
- if (position && !css_tryget(&position->css))
+
+ /*
+ * We cannot take a reference to root because we might race
+ * with root removal and returning NULL would end up in
+ * an endless loop on the iterator user level when root
+ * would be returned all the time.
+ */
+ if (position && position != root &&
+ !css_tryget(&position->css))
position = NULL;
}
return position;
@@ -1126,9 +1134,11 @@ mem_cgroup_iter_load(struct mem_cgroup_r
static void mem_cgroup_iter_update(struct mem_cgroup_reclaim_iter *iter,
struct mem_cgroup *last_visited,
struct mem_cgroup *new_position,
+ struct mem_cgroup *root,
int sequence)
{
- if (last_visited)
+ /* root reference counting symmetric to mem_cgroup_iter_load */
+ if (last_visited && last_visited != root)
css_put(&last_visited->css);
/*
* We store the sequence count from the time @last_visited was
@@ -1203,7 +1213,8 @@ struct mem_cgroup *mem_cgroup_iter(struc
memcg = __mem_cgroup_iter_next(root, last_visited);
if (reclaim) {
- mem_cgroup_iter_update(iter, last_visited, memcg, seq);
+ mem_cgroup_iter_update(iter, last_visited, memcg, root,
+ seq);
if (!memcg)
iter->generation++;
_
Patches currently in -mm which might be from mhocko@xxxxxxx are
mm-mempolicy-remove-unneeded-functions-for-uma-configs.patch
mm-memblock-debug-correct-displaying-of-upper-memory-boundary.patch
memcg-fix-kmem_account_flags-check-in-memcg_can_account_kmem.patch
memcg-make-memcg_update_cache_sizes-static.patch
introduce-for_each_thread-to-replace-the-buggy-while_each_thread.patch
oom_kill-change-oom_killc-to-use-for_each_thread.patch
oom_kill-has_intersects_mems_allowed-needs-rcu_read_lock.patch
oom_kill-add-rcu_read_lock-into-find_lock_task_mm.patch
mm-page_alloc-allow-__gfp_nofail-to-allocate-below-watermarks-after-reclaim.patch
x86-memblock-set-current-limit-to-max-low-memory-address.patch
mm-memblock-debug-dont-free-reserved-array-if-arch_discard_memblock.patch
mm-bootmem-remove-duplicated-declaration-of-__free_pages_bootmem.patch
mm-memblock-remove-unnecessary-inclusions-of-bootmemh.patch
mm-memblock-drop-warn-and-use-smp_cache_bytes-as-a-default-alignment.patch
mm-memblock-reorder-parameters-of-memblock_find_in_range_node.patch
mm-memblock-switch-to-use-numa_no_node-instead-of-max_numnodes.patch
mm-memblock-add-memblock-memory-allocation-apis.patch
mm-memblock-add-memblock-memory-allocation-apis-fix.patch
mm-init-use-memblock-apis-for-early-memory-allocations.patch
mm-printk-use-memblock-apis-for-early-memory-allocations.patch
mm-page_alloc-use-memblock-apis-for-early-memory-allocations.patch
mm-power-use-memblock-apis-for-early-memory-allocations.patch
lib-swiotlbc-use-memblock-apis-for-early-memory-allocations.patch
lib-cpumaskc-use-memblock-apis-for-early-memory-allocations.patch
mm-sparse-use-memblock-apis-for-early-memory-allocations.patch
mm-hugetlb-use-memblock-apis-for-early-memory-allocations.patch
mm-page_cgroup-use-memblock-apis-for-early-memory-allocations.patch
mm-percpu-use-memblock-apis-for-early-memory-allocations.patch
mm-memory_hotplug-use-memblock-apis-for-early-memory-allocations.patch
drivers-firmware-memmapc-use-memblock-apis-for-early-memory-allocations.patch
arch-arm-kernel-use-memblock-apis-for-early-memory-allocations.patch
arch-arm-mm-initc-use-memblock-apis-for-early-memory-allocations.patch
arch-arm-mach-omap2-omap_hwmodc-use-memblock-apis-for-early-memory-allocations.patch
lib-show_memc-show-num_poisoned_pages-when-oom.patch
memcg-oom-lock-mem_cgroup_print_oom_info.patch
mm-page_alloc-warn-for-non-blockable-__gfp_nofail-allocation-failure.patch
memcg-do-not-use-vmalloc-for-mem_cgroup-allocations.patch
slab-clean-up-kmem_cache_create_memcg-error-handling.patch
memcg-slab-kmem_cache_create_memcg-fix-memleak-on-fail-path.patch
memcg-slab-kmem_cache_create_memcg-fix-memleak-on-fail-path-fix.patch
memcg-slab-clean-up-memcg-cache-initialization-destruction.patch
memcg-slab-fix-barrier-usage-when-accessing-memcg_caches.patch
memcg-fix-possible-null-deref-while-traversing-memcg_slab_caches-list.patch
memcg-slab-fix-races-in-per-memcg-cache-creation-destruction.patch
memcg-get-rid-of-kmem_cache_dup.patch
slab-do-not-panic-if-we-fail-to-create-memcg-cache.patch
memcg-slab-rcu-protect-memcg_params-for-root-caches.patch
memcg-remove-kmem_accounted_activated-flag.patch
memcg-rework-memcg_update_kmem_limit-synchronization.patch
mm-new_vma_page-cannot-see-null-vma-for-hugetlb-pages.patch
mm-prevent-setting-of-a-value-less-than-0-to-min_free_kbytes.patch
memcg-do-not-hang-on-oom-when-killed-by-userspace-oom-access-to-memory-reserves.patch
mm-vmscan-shrink-all-slab-objects-if-tight-on-memory.patch
mm-vmscan-call-numa-unaware-shrinkers-irrespective-of-nodemask.patch
mm-vmscan-respect-numa-policy-mask-when-shrinking-slab-on-direct-reclaim.patch
mm-vmscan-move-call-to-shrink_slab-to-shrink_zones.patch
mm-vmscan-remove-shrink_control-arg-from-do_try_to_free_pages.patch
mm-show-message-when-updating-min_free_kbytes-in-thp.patch
mm-memcg-fix-last_dead_count-memory-wastage.patch
mm-memcg-iteration-skip-memcgs-not-yet-fully-initialized.patch
mm-oom-prefer-thread-group-leaders-for-display-purposes.patch
memcg-fix-endless-loop-caused-by-mem_cgroup_iter.patch
memcg-fix-css-reference-leak-and-endless-loop-in-mem_cgroup_iter.patch
proc-fix-the-potential-use-after-free-in-first_tid.patch
proc-change-first_tid-to-use-while_each_thread-rather-than-next_thread.patch
proc-dont-abuse-group_leader-in-proc_task_readdir-paths.patch
proc-fix-f_pos-overflows-in-first_tid.patch
linux-next.patch
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