oops-pattern: add new WARNING pattern

To capture below error:

kern  :warn  : [   57.182374 ] ============================================
kern  :warn  : [   57.182582 ] WARNING: possible recursive locking detected
kern  :warn  : [   57.182788 ] 4.12.0-rc4-wt-ath-05992-g2728455 fengguang#1 Not tainted
kern  :warn  : [   57.183009 ] --------------------------------------------
kern  :warn  : [   57.183237 ] repro-8659a50e./13114 is trying to acquire lock:
kern  :warn  : [   57.183449 ]  (sb_writers#5){.+.+.+}, at: [<ffffffff816956c2>] do_iter_write+0x352/0x7d0
kern  :warn  : [   57.183781 ]
                              but task is already holding lock:
kern  :warn  : [   57.184087 ]  (sb_writers#5){.+.+.+}, at: [<ffffffff81696f6d>] do_sendfile+0x9bd/0xcc0
kern  :warn  : [   57.184407 ]
                              other info that might help us debug this:
kern  :warn  : [   57.184705 ]  Possible unsafe locking scenario:

kern  :warn  : [   57.184998 ]        CPU0
kern  :warn  : [   57.185170 ]        ----
kern  :warn  : [   57.185332 ]   lock(sb_writers#5);
kern  :warn  : [   57.185510 ]   lock(sb_writers#5);
kern  :warn  : [   57.185685 ]
                               *** DEADLOCK ***

kern  :warn  : [   57.186067 ]  May be due to missing lock nesting notation

Signed-off-by: Xiaolong Ye <[email protected]>
Signed-off-by: Philip Li <[email protected]>

etc/oops-pattern

@@ -9,6 +9,7 @@ BUG .* \(.*\): .*
 Oops: .*
 WARNING: at .*
 WARNING: CPU: [0-9]+ PID: [0-9]+ at .*
+WARNING: possible recursive locking detected
 INFO: .*detected stall.*
 INFO: .* cpu=.*
 INFO: Slab 0x.*