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@redhat.com>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/20200723150526.19931-1-lczerner@redhat.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 1cbe3f2..a6de88f 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5512,7 +5512,7 @@ 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;
@@ -5555,6 +5555,14 @@ 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;
@@ -5608,9 +5616,6 @@ 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;
@@ -5758,7 +5763,13 @@ 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;