locking/lockdep: Remove !dir in lock irq usage check

In mark_lock_irq(), the following checks are performed:

   ----------------------------------
  |   ->      | unsafe | read unsafe |
  |----------------------------------|
  | safe      |  F  B  |    F* B*    |
  |----------------------------------|
  | read safe |  F? B* |      -      |
   ----------------------------------

Where:
F: check_usage_forwards
B: check_usage_backwards
*: check enabled by STRICT_READ_CHECKS
?: check enabled by the !dir condition

From checking point of view, the special F? case does not make sense,
whereas it perhaps is made for peroformance concern. As later patch will
address this issue, remove this exception, which makes the checks
consistent later.

With STRICT_READ_CHECKS = 1 which is default, there is no functional
change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-24-duyuyang@gmail.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/lockdep.c

@@ -3235,7 +3235,7 @@ mark_lock_irq(struct task_struct *curr, struct held_lock *this,
 	 * Validate that the lock dependencies don't have conflicting usage
 	 * states.
 	 */
-	if ((!read || !dir || STRICT_READ_CHECKS) &&
+	if ((!read || STRICT_READ_CHECKS) &&
 			!usage(curr, this, excl_bit, state_name(new_bit & ~LOCK_USAGE_READ_MASK)))
 		return 0;