The patch titled
Subject: khugepaged: adjust VM_BUG_ON_MM() in __khugepaged_enter()
has been added to the -mm tree. Its filename is
khugepaged-adjust-vm_bug_on_mm-in-__khugepaged_enter.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/khugepaged-adjust-vm_bug_on_mm-in-__khugepaged_enter.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/khugepaged-adjust-vm_bug_on_mm-in-__khugepaged_enter.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: 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().
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008141503370.18085@eggly.anvils
Fixes: bbe98f9cadff ("khugepaged: khugepaged_test_exit() check mmget_still_valid()")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Song Liu <songliubraving@xxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.8+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/khugepaged.c~khugepaged-adjust-vm_bug_on_mm-in-__khugepaged_enter
+++ a/mm/khugepaged.c
@@ -466,7 +466,7 @@ int __khugepaged_enter(struct mm_struct
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;
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
dma-debug-fix-debug_dma_assert_idle-use-rcu_read_lock.patch
khugepaged-adjust-vm_bug_on_mm-in-__khugepaged_enter.patch
