linux-ext4 - [PATCH] ext4: handle option set by mount flags correctly

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Date:   Thu, 23 Jul 2020 17:05:26 +0200
From:   Lukas Czerner <lczerner@...hat.com>
To:     linux-ext4@...r.kernel.org
Cc:     tytso@....edu
Subject: [PATCH] ext4: handle option set by mount flags correctly

Currently there is a problem with mount options that can be both set by
vfs using mount flags or by a string parsing in ext4.

i_version/iversion options gets lost after remount, for example

$ mount -o i_version /dev/pmem0 /mnt
$ grep pmem0 /proc/self/mountinfo | grep i_version
310 95 259:0 / /mnt rw,relatime shared:163 - ext4 /dev/pmem0 rw,seclabel,i_version
$ mount -o remount,ro /mnt
$ grep pmem0 /proc/self/mountinfo | grep i_version

nolazytime gets ignored by ext4 on remount, for example

$ mount -o lazytime /dev/pmem0 /mnt
$ grep pmem0 /proc/self/mountinfo | grep lazytime
310 95 259:0 / /mnt rw,relatime shared:163 - ext4 /dev/pmem0 rw,lazytime,seclabel
$ mount -o remount,nolazytime /mnt
$ grep pmem0 /proc/self/mountinfo | grep lazytime
310 95 259:0 / /mnt rw,relatime shared:163 - ext4 /dev/pmem0 rw,lazytime,seclabel

Fix it by applying the SB_LAZYTIME and SB_I_VERSION flags from *flags to
s_flags before we parse the option and use the resulting state of the
same flags in *flags at the end of successful remount.

Signed-off-by: Lukas Czerner <lczerner@...hat.com>
---
 fs/ext4/super.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 330957ed1f05..caab4c57f909 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5445,7 +5445,7 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
 {
 	struct ext4_super_block *es;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
-	unsigned long old_sb_flags;
+	unsigned long old_sb_flags, vfs_flags;
 	struct ext4_mount_options old_opts;
 	int enable_quota = 0;
 	ext4_group_t g;
@@ -5488,6 +5488,14 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
 	if (sbi->s_journal && sbi->s_journal->j_task->io_context)
 		journal_ioprio = sbi->s_journal->j_task->io_context->ioprio;
 
+	/*
+	 * Some options can be enabled by ext4 and/or by VFS mount flag
+	 * either way we need to make sure it matches in both *flags and
+	 * s_flags. Copy those selected flags from *flags to s_flags
+	 */
+	vfs_flags = SB_LAZYTIME | SB_I_VERSION;
+	sb->s_flags = (sb->s_flags & ~vfs_flags) | (*flags & vfs_flags);
+
 	if (!parse_options(data, sb, NULL, &journal_ioprio, 1)) {
 		err = -EINVAL;
 		goto restore_opts;
@@ -5541,9 +5549,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
 		set_task_ioprio(sbi->s_journal->j_task, journal_ioprio);
 	}
 
-	if (*flags & SB_LAZYTIME)
-		sb->s_flags |= SB_LAZYTIME;
-
 	if ((bool)(*flags & SB_RDONLY) != sb_rdonly(sb)) {
 		if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED) {
 			err = -EROFS;
@@ -5675,7 +5680,13 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
 	}
 #endif
 
-	*flags = (*flags & ~SB_LAZYTIME) | (sb->s_flags & SB_LAZYTIME);
+	/*
+	 * Some options can be enabled by ext4 and/or by VFS mount flag
+	 * either way we need to make sure it matches in both *flags and
+	 * s_flags. Copy those selected flags from s_flags to *flags
+	 */
+	*flags = (*flags & ~vfs_flags) | (sb->s_flags & vfs_flags);
+
 	ext4_msg(sb, KERN_INFO, "re-mounted. Opts: %s", orig_data);
 	kfree(orig_data);
 	return 0;
-- 
2.21.3