swim3: fix interruptible_sleep_on race

interruptible_sleep_on is racy and going away. This replaces the one
caller in the swim3 driver with the equivalent race-free
wait_event_interruptible call. Since we're here already, this
also fixes the case where we get interrupted from atomic context,
which used to just spin in the loop.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/swim3.c

@@ -30,6 +30,7 @@
 #include <linux/mutex.h>
 #include <linux/module.h>
 #include <linux/spinlock.h>
+#include <linux/wait.h>
 #include <asm/io.h>
 #include <asm/dbdma.h>
 #include <asm/prom.h>
@@ -840,14 +841,17 @@ static int grab_drive(struct floppy_state *fs, enum swim_state state,
 	spin_lock_irqsave(&swim3_lock, flags);
 	if (fs->state != idle && fs->state != available) {
 		++fs->wanted;
-		while (fs->state != available) {
+		/* this will enable irqs in order to sleep */
+		if (!interruptible)
+			wait_event_lock_irq(fs->wait,
+                                        fs->state == available,
+                                        swim3_lock);
+		else if (wait_event_interruptible_lock_irq(fs->wait,
+					fs->state == available,
+					swim3_lock)) {
+			--fs->wanted;
 			spin_unlock_irqrestore(&swim3_lock, flags);
-			if (interruptible && signal_pending(current)) {
-				--fs->wanted;
-				return -EINTR;
-			}
-			interruptible_sleep_on(&fs->wait);
-			spin_lock_irqsave(&swim3_lock, flags);
+			return -EINTR;
 		}
 		--fs->wanted;
 	}