khugepaged: adjust VM_BUG_ON_MM() in __khugepaged_enter()
[ Upstream commitf3f99d63a8
] 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:bbe98f9cad
("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>
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@ -438,7 +438,7 @@ int __khugepaged_enter(struct mm_struct *mm)
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return -ENOMEM;
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/* __khugepaged_exit() must not run from under us */
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VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
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VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm);
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if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
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free_mm_slot(mm_slot);
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return 0;
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