Currently, in safe->unsafe detection, lockdep misses the fact that a
LOCK_ENABLED_IRQ_*_READ usage and a LOCK_USED_IN_IRQ_*_READ usage may
cause deadlock too, for example:

	P1                          P2
	<irq disabled>
	write_lock(l1);             <irq enabled>
				    read_lock(l2);
	write_lock(l2);
				    <in irq>
				    read_lock(l1);

Actually, all of the following cases may cause deadlocks:

	LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*
	LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*
	LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*_READ
	LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*_READ

To fix this, we need to 1) change the calculation of exclusive_mask() so
that READ bits are not dropped and 2) always call usage() in
mark_lock_irq() to check usage deadlocks, even when the new usage of the
lock is READ.

Besides, adjust usage_match() and usage_acculumate() to recursive read
lock changes.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-12-boqun.feng@gmail.com