Commit f3f99d63 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds

khugepaged: adjust VM_BUG_ON_MM() in __khugepaged_enter()

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: bbe98f9c ("khugepaged: khugepaged_test_exit() check mmget_still_valid()")
Reported-by: default avatarsyzbot <syzkaller@googlegroups.com>
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Acked-by: default avatarYang 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.anvilsSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d5a16959
...@@ -466,7 +466,7 @@ int __khugepaged_enter(struct mm_struct *mm) ...@@ -466,7 +466,7 @@ int __khugepaged_enter(struct mm_struct *mm)
return -ENOMEM; return -ENOMEM;
/* __khugepaged_exit() must not run from under us */ /* __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))) { if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
free_mm_slot(mm_slot); free_mm_slot(mm_slot);
return 0; return 0;
......
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