af_packet: block BH in prb_shutdown_retire_blk_timer()

Currently we're using plain spin_lock() in prb_shutdown_retire_blk_timer(),
however the timer might fire right in the middle and thus try to re-aquire
the same spinlock, leaving us in a endless loop.

To fix that, use the spin_lock_bh() to block it.

Fixes: f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation.")
CC: "David S. Miller" <[e-mail]>
CC: Daniel Borkmann <[e-mail]>
CC: Willem de Bruijn <[e-mail]>
CC: Phil Sutter <[e-mail]>
CC: Eric Dumazet <[e-mail]>
Reported-by: Jan Stancek <[e-mail]>
Tested-by: Jan Stancek <[e-mail]>
Signed-off-by: Veaceslav Falico <[e-mail]>
Acked-by: Daniel Borkmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/packet/af_packet.c

···
 
 	pkc = tx_ring ? &po->tx_ring.prb_bdqc : &po->rx_ring.prb_bdqc;
 
-	spin_lock(&rb_queue->lock);
+	spin_lock_bh(&rb_queue->lock);
 	pkc->delete_blk_timer = 1;
-	spin_unlock(&rb_queue->lock);
+	spin_unlock_bh(&rb_queue->lock);
 
 	prb_del_retire_blk_timer(pkc);
 }