From: Hugh Dickins <hughd@google.com> stable inclusion from linux-4.19.142 commit 2ef7ebb143705147bc74db2bc1bd0214c212e6bc -------------------------------- [ Upstream commit f3f99d63a8156c7a4a6b20aac22b53c5579c7dc1 ] syzbot crashes on the VM_BUG_ON_MM(khugepaged_test_exit(mm), mm) in __khugepaged_enter(): yes, when one thread is about to dump core, has set core_state, and is waiting for others, another might do something calling __khugepaged_enter(), which now crashes because I lumped the core_state test (known as "mmget_still_valid") into khugepaged_test_exit(). I still think it's best to lump them together, so just in this exceptional case, check mm->mm_users directly instead of khugepaged_test_exit(). Fixes: bbe98f9cadff ("khugepaged: khugepaged_test_exit() check mmget_still_valid()") Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Yang Shi <shy828301@gmail.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Song Liu <songliubraving@fb.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Eric Dumazet <edumazet@google.com> Cc: <stable@vger.kernel.org> [4.8+] Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008141503370.18085@eggly.anvils Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com> --- mm/khugepaged.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index fbb3ac9ce086..f37be43f8cae 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -427,7 +427,7 @@ int __khugepaged_enter(struct mm_struct *mm) return -ENOMEM; /* __khugepaged_exit() must not run from under us */ - VM_BUG_ON_MM(khugepaged_test_exit(mm), mm); + VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm); if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) { free_mm_slot(mm_slot); return 0; -- 2.25.1