mm/ksm: fix race with VMA iteration and mm_struct teardown

exit_mmap() will tear down the VMAs and maple tree with the mmap_lock held
in write mode.  Ensure that the maple tree is still valid by checking
ksm_test_exit() after taking the mmap_lock in read mode, but before the
for_each_vma() iterator dereferences a destroyed maple tree.

Since the maple tree is destroyed, the flags telling lockdep to check an
external lock has been cleared.  Skip the for_each_vma() iterator to avoid
dereferencing a maple tree without the external lock flag, which would
create a lockdep warning.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: a5f18ba07276 ("mm/ksm: use vma iterators instead of vma linked list")
Signed-off-by: Liam R. Howlett <[email protected]>
Reported-by: Pengfei Xu <[email protected]>
  Link: https://lore.kernel.org/lkml/[email protected]/
Reported-by: [email protected]
  Link: https://syzkaller.appspot.com/bug?id=64a3e95957cd3deab99df7cd7b5a9475af92c93e
Acked-by: David Hildenbrand <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions