linux-kernel - [PATCH] ext4: Fix journal_ioprio mount option handling

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Date:   Mon, 18 Apr 2022 14:05:45 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org
Cc:     "Theodore Ts'o" <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] ext4: Fix journal_ioprio mount option handling

In __ext4_super() we always overwrote the user specified journal_ioprio
value with a default value, expecting  parse_apply_sb_mount_options() to
later correctly set ctx->journal_ioprio to the user specified value.
However, if parse_apply_sb_mount_options() returned early because of
empty sbi->es_s->s_mount_opts, the correct journal_ioprio value was
never set.

This patch fixes __ext4_super() to only use the default value if the
user has not specified any value for journal_ioprio.

Similarly, the remount behavior was to either use journal_ioprio
value specified during initial mount, or use the default value
irrespective of the journal_ioprio value specified during remount.
This patch modifies this to first check if a new value for ioprio
has been passed during remount and apply it. Incase, no new value is
passed, use the value specified during initial mount.

Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
---
 fs/ext4/super.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c5a9ffbf7f4f..bfd767c51203 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4427,7 +4427,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 	int silent = fc->sb_flags & SB_SILENT;

 	/* Set defaults for the variables that will be set during parsing */
-	ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
+	if (!(ctx->spec & EXT4_SPEC_JOURNAL_IOPRIO))
+		ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;

 	sbi->s_inode_readahead_blks = EXT4_DEF_INODE_READAHEAD_BLKS;
 	sbi->s_sectors_written_start =
@@ -6289,7 +6290,6 @@ static int __ext4_remount(struct fs_context *fc, struct super_block *sb)
 	char *to_free[EXT4_MAXQUOTAS];
 #endif

-	ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;

 	/* Store the original options */
 	old_sb_flags = sb->s_flags;
@@ -6315,9 +6315,14 @@ static int __ext4_remount(struct fs_context *fc, struct super_block *sb)
 		} else
 			old_opts.s_qf_names[i] = NULL;
 #endif
-	if (sbi->s_journal && sbi->s_journal->j_task->io_context)
-		ctx->journal_ioprio =
-			sbi->s_journal->j_task->io_context->ioprio;
+	if (!(ctx->spec & EXT4_SPEC_JOURNAL_IOPRIO)) {
+		if (sbi->s_journal && sbi->s_journal->j_task->io_context)
+			ctx->journal_ioprio =
+				sbi->s_journal->j_task->io_context->ioprio;
+		else
+			ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
+
+	}

 	ext4_apply_options(fc, sb);

-- 
2.27.0