ext4: remove the obsolete/broken EXT4_IOC_WAIT_FOR_READONLY ioctl

There are no users of the EXT4_IOC_WAIT_FOR_READONLY ioctl, and it is
also broken.  No one sets the set_ro_timer, no one wakes up us and our
state is set to TASK_INTERRUPTIBLE not RUNNING.  So remove it.
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -564,9 +564,6 @@ struct ext4_new_group_data {
 #define	EXT4_IOC_SETVERSION		_IOW('f', 4, long)
 #define	EXT4_IOC_GETVERSION_OLD		FS_IOC_GETVERSION
 #define	EXT4_IOC_SETVERSION_OLD		FS_IOC_SETVERSION
-#ifdef CONFIG_JBD2_DEBUG
-#define EXT4_IOC_WAIT_FOR_READONLY	_IOR('f', 99, long)
-#endif
 #define EXT4_IOC_GETRSVSZ		_IOR('f', 5, long)
 #define EXT4_IOC_SETRSVSZ		_IOW('f', 6, long)
 #define EXT4_IOC_GROUP_EXTEND		_IOW('f', 7, unsigned long)
@@ -589,9 +586,6 @@ struct ext4_new_group_data {
 #define EXT4_IOC32_SETRSVSZ		_IOW('f', 6, int)
 #define EXT4_IOC32_GROUP_EXTEND		_IOW('f', 7, unsigned int)
 #define EXT4_IOC32_GROUP_ADD		_IOW('f', 8, struct compat_ext4_new_group_input)
-#ifdef CONFIG_JBD2_DEBUG
-#define EXT4_IOC32_WAIT_FOR_READONLY	_IOR('f', 99, int)
-#endif
 #define EXT4_IOC32_GETVERSION_OLD	FS_IOC32_GETVERSION
 #define EXT4_IOC32_SETVERSION_OLD	FS_IOC32_SETVERSION
 #endif
@@ -1171,10 +1165,6 @@ struct ext4_sb_info {
 	u32 s_max_batch_time;
 	u32 s_min_batch_time;
 	struct block_device *journal_bdev;
-#ifdef CONFIG_JBD2_DEBUG
-	struct timer_list turn_ro_timer;	/* For turning read-only (crash simulation) */
-	wait_queue_head_t ro_wait_queue;	/* For people waiting for the fs to go read-only */
-#endif
 #ifdef CONFIG_QUOTA
 	char *s_qf_names[MAXQUOTAS];		/* Names of quota files with journalled quota */
 	int s_jquota_fmt;			/* Format of quota to use */

fs/ext4/ioctl.c

@@ -174,29 +174,6 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		mnt_drop_write(filp->f_path.mnt);
 		return err;
 	}
-#ifdef CONFIG_JBD2_DEBUG
-	case EXT4_IOC_WAIT_FOR_READONLY:
-		/*
-		 * This is racy - by the time we're woken up and running,
-		 * the superblock could be released.  And the module could
-		 * have been unloaded.  So sue me.
-		 *
-		 * Returns 1 if it slept, else zero.
-		 */
-		{
-			DECLARE_WAITQUEUE(wait, current);
-			int ret = 0;
-
-			set_current_state(TASK_INTERRUPTIBLE);
-			add_wait_queue(&EXT4_SB(sb)->ro_wait_queue, &wait);
-			if (timer_pending(&EXT4_SB(sb)->turn_ro_timer)) {
-				schedule();
-				ret = 1;
-			}
-			remove_wait_queue(&EXT4_SB(sb)->ro_wait_queue, &wait);
-			return ret;
-		}
-#endif
 	case EXT4_IOC_GROUP_EXTEND: {
 		ext4_fsblk_t n_blocks_count;
 		int err, err2=0;
@@ -421,11 +398,6 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case EXT4_IOC32_SETVERSION_OLD:
 		cmd = EXT4_IOC_SETVERSION_OLD;
 		break;
-#ifdef CONFIG_JBD2_DEBUG
-	case EXT4_IOC32_WAIT_FOR_READONLY:
-		cmd = EXT4_IOC_WAIT_FOR_READONLY;
-		break;
-#endif
 	case EXT4_IOC32_GETRSVSZ:
 		cmd = EXT4_IOC_GETRSVSZ;
 		break;