[PATCH 5.17 0135/1126] ext4: make mb_optimize_scan option work with set/unset mount cmd

[Greg Kroah-Hartman]

From: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>

commit 27b38686a3bb601db48901dbc4e2fc5d77ffa2c1 upstream.

After moving to the new mount API, mb_optimize_scan mount option
handling was not working as expected due to the parsed value always
being overwritten by default. Refactor and fix this to the expected
behavior described below:

*  mb_optimize_scan=1 - On
*  mb_optimize_scan=0 - Off
*  mb_optimize_scan not passed - On if no. of BGs > threshold else off
*  Remounts retain previous value unless we explicitly pass the option
   with a new value

Fixes: cebe85d570cf ("ext4: switch to the new mount api")
Cc: stable@xxxxxxxxxx
Reported-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
Reviewed-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/c98970fe99f26718586d02e942f293300fb48ef3.1646732698.git.ojaswin@xxxxxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/ext4/super.c |   24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2021,12 +2021,12 @@ static int ext4_set_test_dummy_encryptio
 #define EXT4_SPEC_s_commit_interval		(1 << 16)
 #define EXT4_SPEC_s_fc_debug_max_replay		(1 << 17)
 #define EXT4_SPEC_s_sb_block			(1 << 18)
+#define EXT4_SPEC_mb_optimize_scan		(1 << 19)
 
 struct ext4_fs_context {
 	char		*s_qf_names[EXT4_MAXQUOTAS];
 	char		*test_dummy_enc_arg;
 	int		s_jquota_fmt;	/* Format of quota to use */
-	int		mb_optimize_scan;
 #ifdef CONFIG_EXT4_DEBUG
 	int s_fc_debug_max_replay;
 #endif
@@ -2451,12 +2451,17 @@ static int ext4_parse_param(struct fs_co
 			ctx_clear_mount_opt(ctx, m->mount_opt);
 		return 0;
 	case Opt_mb_optimize_scan:
-		if (result.int_32 != 0 && result.int_32 != 1) {
+		if (result.int_32 == 1) {
+			ctx_set_mount_opt2(ctx, EXT4_MOUNT2_MB_OPTIMIZE_SCAN);
+			ctx->spec |= EXT4_SPEC_mb_optimize_scan;
+		} else if (result.int_32 == 0) {
+			ctx_clear_mount_opt2(ctx, EXT4_MOUNT2_MB_OPTIMIZE_SCAN);
+			ctx->spec |= EXT4_SPEC_mb_optimize_scan;
+		} else {
 			ext4_msg(NULL, KERN_WARNING,
 				 "mb_optimize_scan should be set to 0 or 1.");
 			return -EINVAL;
 		}
-		ctx->mb_optimize_scan = result.int_32;
 		return 0;
 	}
 
@@ -4369,7 +4374,6 @@ static int __ext4_fill_super(struct fs_c
 
 	/* Set defaults for the variables that will be set during parsing */
 	ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
-	ctx->mb_optimize_scan = DEFAULT_MB_OPTIMIZE_SCAN;
 
 	sbi->s_inode_readahead_blks = EXT4_DEF_INODE_READAHEAD_BLKS;
 	sbi->s_sectors_written_start =
@@ -5320,12 +5324,12 @@ no_journal:
 	 * turned off by passing "mb_optimize_scan=0". This can also be
 	 * turned on forcefully by passing "mb_optimize_scan=1".
 	 */
-	if (ctx->mb_optimize_scan == 1)
-		set_opt2(sb, MB_OPTIMIZE_SCAN);
-	else if (ctx->mb_optimize_scan == 0)
-		clear_opt2(sb, MB_OPTIMIZE_SCAN);
-	else if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
-		set_opt2(sb, MB_OPTIMIZE_SCAN);
+	if (!(ctx->spec & EXT4_SPEC_mb_optimize_scan)) {
+		if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
+			set_opt2(sb, MB_OPTIMIZE_SCAN);
+		else
+			clear_opt2(sb, MB_OPTIMIZE_SCAN);
+	}
 
 	err = ext4_mb_init(sb);
 	if (err) {