sbitmap: Protect swap_lock from softirqs

The swap_lock used by sbitmap has a chain with locks taken from softirq,
but the swap_lock is not protected from being preempted by softirqs.

A chain exists of:

 sbq->ws[i].wait -> dispatch_wait_lock -> swap_lock

Where the sbq->ws[i].wait lock can be taken from softirq context, which
means all locks below it in the chain must also be protected from
softirqs.
Reported-by: NClark Williams <williams@redhat.com>
Fixes: 58ab5e32 ("sbitmap: silence bogus lockdep IRQ warning")
Fixes: ea86ea2c ("sbitmap: amortize cost of clearing bits")
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

lib/sbitmap.c

@@ -26,14 +26,9 @@
 static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
 {
 	unsigned long mask, val;
-	unsigned long __maybe_unused flags;
 	bool ret = false;
 
-	/* Silence bogus lockdep warning */
-#if defined(CONFIG_LOCKDEP)
-	local_irq_save(flags);
-#endif
-	spin_lock(&sb->map[index].swap_lock);
+	spin_lock_bh(&sb->map[index].swap_lock);
 
 	if (!sb->map[index].cleared)
 		goto out_unlock;
@@ -54,10 +49,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
 
 	ret = true;
 out_unlock:
-	spin_unlock(&sb->map[index].swap_lock);
-#if defined(CONFIG_LOCKDEP)
-	local_irq_restore(flags);
-#endif
+	spin_unlock_bh(&sb->map[index].swap_lock);
 	return ret;
 }