ext4: make mb_optimize_scan option work with set/unset mount cmd

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@kernel.org
Reported-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/c98970fe99f26718586d02e942f293300fb48ef3.1646732698.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 1e5f499..4120a74 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2021,12 +2021,12 @@ static int ext4_set_test_dummy_encryption(struct super_block *sb, char *arg)
 #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
@@ -2464,12 +2464,17 @@ static int ext4_parse_param(struct fs_context *fc, struct fs_parameter *param)
                        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;
        }
 
@@ -4398,7 +4403,6 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 
        /* 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 =
@@ -5349,12 +5353,12 @@ 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) {