[PATCH] ovl: sync dirty data when remounting to ro mode

[PATCH] ovl: sync dirty data when remounting to ro mode

[Chengguang Xu]

sync_filesystem() does not sync dirty data for readonly
filesystem during umount, so before changing to readonly
filesystem we should sync dirty data for data integrity.

Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
---
 fs/overlayfs/super.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index f57aa348dcd6..1bab326342bc 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -364,11 +364,20 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 static int ovl_remount(struct super_block *sb, int *flags, char *data)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;
+	struct super_block *upper_sb;
+	int ret = 0;
 
 	if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
 		return -EROFS;
 
-	return 0;
+	if (*flags & SB_RDONLY && !sb_rdonly(sb)) {
+		upper_sb = ofs->upper_mnt->mnt_sb;
+		down_read(&upper_sb->s_umount);
+		ret = sync_filesystem(upper_sb);
+		up_read(&upper_sb->s_umount);
+	}
+
+	return ret;
 }
 
 static const struct super_operations ovl_super_operations = {
-- 
2.20.1

Re: [PATCH] ovl: sync dirty data when remounting to ro mode

[Miklos Szeredi]

On Wed, Apr 22, 2020 at 6:29 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
>
> sync_filesystem() does not sync dirty data for readonly
> filesystem during umount, so before changing to readonly
> filesystem we should sync dirty data for data integrity.

Isn't the same true for ->put_super()?

Thanks,
Miklos

Re: [PATCH] ovl: sync dirty data when remounting to ro mode

[Chengguang Xu]

 ---- 在 星期三, 2020-04-22 15:29:33 Miklos Szeredi <miklos@szeredi.hu> 撰写 ----
 > On Wed, Apr 22, 2020 at 6:29 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
 > >
 > > sync_filesystem() does not sync dirty data for readonly
 > > filesystem during umount, so before changing to readonly
 > > filesystem we should sync dirty data for data integrity.
 > 
 > Isn't the same true for ->put_super()?
 > 

Before getting into ->put_super(),  dirty data have been synced through below functions,
so I think we don't have to worry about ->put_super().

kill_anon_super()
  generic_shutdown_super()
     sync_filesystem()


Thanks,
cgxu

Re: [PATCH] ovl: sync dirty data when remounting to ro mode

[Miklos Szeredi]

On Wed, Apr 22, 2020 at 10:13 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
>
>  ---- 在 星期三, 2020-04-22 15:29:33 Miklos Szeredi <miklos@szeredi.hu> 撰写 ----
>  > On Wed, Apr 22, 2020 at 6:29 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
>  > >
>  > > sync_filesystem() does not sync dirty data for readonly
>  > > filesystem during umount, so before changing to readonly
>  > > filesystem we should sync dirty data for data integrity.
>  >
>  > Isn't the same true for ->put_super()?
>  >
>
> Before getting into ->put_super(),  dirty data have been synced through below functions,
> so I think we don't have to worry about ->put_super().
>
> kill_anon_super()
>   generic_shutdown_super()
>      sync_filesystem()

Okay, makes sense.

Thanks,
Miklos