futex: Test for pi_mutex on fault in futex_wait_requeue_pi()

futex: Test for pi_mutex on fault in futex_wait_requeue_pi()

If fixup_pi_state_owner() faults, pi_mutex may be NULL. Test
for pi_mutex != NULL before testing the owner against current
and possibly unlocking it.

Signed-off-by: Darren Hart <[email protected]>
Cc: Dave Jones <[email protected]>
Cc: Dan Carpenter <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/dc59890338fc413606f04e5c5b131530734dae3d.1342809673.git.dvhart@linux.intel.com
Signed-off-by: Thomas Gleixner <[email protected]>