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authorHugh Dickins <hughd@google.com>2020-08-21 03:42:02 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-21 19:52:53 +0300
commitf3f99d63a8156c7a4a6b20aac22b53c5579c7dc1 (patch)
treec4fbc902f78e39e40b6dd07c55b31316eb38e7d8
parentd5a1695977cf60d3f7b387f4d18bd2fb2a9a7a01 (diff)
downloadlinux-f3f99d63a8156c7a4a6b20aac22b53c5579c7dc1.tar.xz
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: 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>
-rw-r--r--mm/khugepaged.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 15a9af791014..e749e568e1ea 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -466,7 +466,7 @@ 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;