mm: do not call do_fault_around for non-linear fault
Ingo Korb reported that "repeated mapping of the same file on tmpfs using remap_file_pages sometimes triggers a BUG at mm/filemap.c:202 when the process exits". He bisected the bug to d7c17551 ("mm: implement ->map_pages for shmem/tmpfs"), although the bug was actually added by commit 8c6e50b0 ("mm: introduce vm_ops->map_pages()"). The problem is caused by calling do_fault_around for a _non-linear_ fault. In this case pgoff is shifted and might become negative during calculation. Faulting around non-linear page-fault makes no sense and breaks the logic in do_fault_around because pgoff is shifted. Signed-off-by: NKonstantin Khlebnikov <koct9i@gmail.com> Reported-by: NIngo Korb <ingo.korb@tu-dortmund.de> Tested-by: NIngo Korb <ingo.korb@tu-dortmund.de> Cc: Hugh Dickins <hughd@google.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Dave Jones <davej@redhat.com> Cc: Ning Qu <quning@google.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: <stable@vger.kernel.org> [3.15.x] Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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