ARM: Initialize ptl->lock for vector page

Without this patch, ARM can not use SPLIT_PTLOCK_CPUS if
PREEMPT_RT_FULL=y because vectors_user_mapping() creates a
VM_ALWAYSDUMP mapping of the vector page (address 0xffff0000), but no
ptl->lock has been allocated for the page.  An attempt to coredump
that page will result in a kernel NULL pointer dereference when
follow_page() attempts to lock the page.

The call tree to the NULL pointer dereference is:

   do_notify_resume()
      get_signal_to_deliver()
         do_coredump()
            elf_core_dump()
               get_dump_page()
                  __get_user_pages()
                     follow_page()
                        pte_offset_map_lock() <----- a #define
                           ...
                              rt_spin_lock()

The underlying problem is exposed by mm-shrink-the-page-frame-to-rt-size.patch.

Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
Cc: Frank <Frank_Rowand@sonyusa.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/4E87C535.2030907@am.sony.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

0 files changed, 0 insertions, 0 deletions