From: Johannes Weiner hannes@cmpxchg.org
mainline inclusion from mainline-v5.13-rc1 commit 9317d0fffeb4c3929069cfc7377cfa2a7cd36d1d category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5244N CVE: NA backport: openEuler-22.03-LTS
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When the unsigned page_counter underflows, even just by a few pages, a cgroup will not be able to run anything afterwards and trigger the OOM killer in a loop.
Underflows shouldn't happen, but when they do in practice, we may just be off by a small amount that doesn't interfere with the normal operation - consequences don't need to be that dire.
Reset the page_counter to 0 upon underflow. We'll issue a warning that the accounting will be off and then try to keep limping along.
[ We used to do this with the original res_counter, where it was a more straight-forward correction inside the spinlock section. I didn't carry it forward into the lockless page counters for simplicity, but it turns out this is quite useful in practice. ]
Link: https://lkml.kernel.org/r/20210408143155.2679744-1-hannes@cmpxchg.org Signed-off-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Michal Hocko mhocko@suse.com Acked-by: Chris Down chris@chrisdown.name Reviewed-by: Shakeel Butt shakeelb@google.com Cc: Hugh Dickins hughd@google.com Cc: Roman Gushchin guro@fb.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Ma Wupeng mawupeng1@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- mm/page_counter.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/mm/page_counter.c b/mm/page_counter.c index b24a60b28bb0..6d8715e3255d 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -52,9 +52,13 @@ void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages) long new;
new = atomic_long_sub_return(nr_pages, &counter->usage); - propagate_protected_usage(counter, new); /* More uncharges than charges? */ - WARN_ON_ONCE(new < 0); + if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n", + new, nr_pages)) { + new = 0; + atomic_long_set(&counter->usage, new); + } + propagate_protected_usage(counter, new); }
/**