• Kirill A. Shutemov's avatar
    mm, thp: fix infinite loop on memcg OOM · 9845cbbd
    Kirill A. Shutemov authored
    Masayoshi Mizuma reported a bug with the hang of an application under
    the memcg limit.  It happens on write-protection fault to huge zero page
    
    If we successfully allocate a huge page to replace zero page but hit the
    memcg limit we need to split the zero page with split_huge_page_pmd()
    and fallback to small pages.
    
    The other part of the problem is that VM_FAULT_OOM has special meaning
    in do_huge_pmd_wp_page() context.  __handle_mm_fault() expects the page
    to be split if it sees VM_FAULT_OOM and it will will retry page fault
    handling.  This causes an infinite loop if the page was not split.
    
    do_huge_pmd_wp_zero_page_fallback() can return VM_FAULT_OOM if it failed
    to allocate one small page, so fallback to small pages will not help.
    
    The solution for this part is to replace VM_FAULT_OOM with
    VM_FAULT_FALLBACK is fallback required.
    Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Reported-by: default avatarMasayoshi Mizuma <m.mizuma@jp.fujitsu.com>
    Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    9845cbbd
memory.c 116 KB