[SCSI] sd: fix medium-removal bug

Commit 409f3499 (scsi/sd: remove big
kernel lock) introduced a bug in the sd_release routine.  Medium
removal should be allowed when the number of open file references
drops to 0, not when it becomes non-zero.

This patch (as1414) adjusts the test to fix the bug.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NJames Bottomley <James.Bottomley@suse.de>

drivers/scsi/sd.c

@@ -870,7 +870,7 @@ static int sd_release(struct gendisk *disk, fmode_t mode)
 
 	SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp, "sd_release\n"));
 
-	if (atomic_dec_return(&sdkp->openers) && sdev->removable) {
+	if (atomic_dec_return(&sdkp->openers) == 0 && sdev->removable) {
 		if (scsi_block_when_processing_errors(sdev))
 			scsi_set_medium_removal(sdev, SCSI_REMOVAL_ALLOW);
 	}