__replace_page() wronlgy calls mem_cgroup_cancel_charge() in "success" path, it should only do this if page_check_address() fails.
This means that every enable/disable leads to unbalanced mem_cgroup_uncharge() from put_page(old_page), it is trivial to underflow the page_counter->count and trigger OOM. Reported-and-tested-by: Brenden Blanco <[email protected]> Signed-off-by: Oleg Nesterov <[email protected]> Acked-by: Michal Hocko <[email protected]> Reviewed-by: Johannes Weiner <[email protected]> Fixes: 00501b531c47 ("mm: memcontrol: rewrite charge API") Cc: [email protected] # 3.17+ --- kernel/events/uprobes.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index b7a525a..8c50276 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -172,8 +172,10 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); err = -EAGAIN; ptep = page_check_address(page, mm, addr, &ptl, 0); - if (!ptep) + if (!ptep) { + mem_cgroup_cancel_charge(kpage, memcg, false); goto unlock; + } get_page(kpage); page_add_new_anon_rmap(kpage, vma, addr, false); @@ -200,7 +202,6 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, err = 0; unlock: - mem_cgroup_cancel_charge(kpage, memcg, false); mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); unlock_page(page); return err; -- 2.5.0
