mm: memcontrol: do not miss MEMCG_MAX events for enforced allocations

Yafang Shao reported an issue related to the accounting of bpf memory:
if a bpf map is charged indirectly for memory consumed from an
interrupt context and allocations are enforced, MEMCG_MAX events are
not raised.

It's not/less of an issue in a generic case because consequent
allocations from a process context will trigger the direct reclaim and
MEMCG_MAX events will be raised.  However a bpf map can belong to a
dying/abandoned memory cgroup, so there will be no allocations from a
process context and no MEMCG_MAX events will be triggered.

Link: https://lkml.kernel.org/r/20220702033521.64630-1-roman.gushchin@linux.dev
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Reported-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c5bfb3e..767f49a 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2577,6 +2577,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
        bool passed_oom = false;
        bool may_swap = true;
        bool drained = false;
+       bool raised_max_event = false;
        unsigned long pflags;
 
 retry:
@@ -2616,6 +2617,7 @@ retry:
                goto nomem;
 
        memcg_memory_event(mem_over_limit, MEMCG_MAX);
+       raised_max_event = true;
 
        psi_memstall_enter(&pflags);
        nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,
@@ -2682,6 +2684,13 @@ nomem:
        if (!(gfp_mask & (__GFP_NOFAIL | __GFP_HIGH)))
                return -ENOMEM;
 force:
+       /*
+        * If the allocation has to be enforced, don't forget to raise
+        * a MEMCG_MAX event.
+        */
+       if (!raised_max_event)
+               memcg_memory_event(mem_over_limit, MEMCG_MAX);
+
        /*
         * The allocation either can't fail or will lead to more memory
         * being freed very soon.  Allow memory usage go over the limit