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    Subject[PATCH 5.15 01/28] devtmpfs regression fix: reconfigure on each mount
    Date
    From: NeilBrown <neilb@suse.de>

    commit a6097180d884ddab769fb25588ea8598589c218c upstream.

    Prior to Linux v5.4 devtmpfs used mount_single() which treats the given
    mount options as "remount" options, so it updates the configuration of
    the single super_block on each mount.

    Since that was changed, the mount options used for devtmpfs are ignored.
    This is a regression which affect systemd - which mounts devtmpfs with
    "-o mode=755,size=4m,nr_inodes=1m".

    This patch restores the "remount" effect by calling reconfigure_single()

    Fixes: d401727ea0d7 ("devtmpfs: don't mix {ramfs,shmem}_fill_super() with mount_single()")
    Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: NeilBrown <neilb@suse.de>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/base/devtmpfs.c | 7 +++++++
    fs/super.c | 4 ++--
    include/linux/fs_context.h | 2 ++
    3 files changed, 11 insertions(+), 2 deletions(-)

    --- a/drivers/base/devtmpfs.c
    +++ b/drivers/base/devtmpfs.c
    @@ -59,8 +59,15 @@ static struct dentry *public_dev_mount(s
    const char *dev_name, void *data)
    {
    struct super_block *s = mnt->mnt_sb;
    + int err;
    +
    atomic_inc(&s->s_active);
    down_write(&s->s_umount);
    + err = reconfigure_single(s, flags, data);
    + if (err < 0) {
    + deactivate_locked_super(s);
    + return ERR_PTR(err);
    + }
    return dget(s->s_root);
    }

    --- a/fs/super.c
    +++ b/fs/super.c
    @@ -1421,8 +1421,8 @@ struct dentry *mount_nodev(struct file_s
    }
    EXPORT_SYMBOL(mount_nodev);

    -static int reconfigure_single(struct super_block *s,
    - int flags, void *data)
    +int reconfigure_single(struct super_block *s,
    + int flags, void *data)
    {
    struct fs_context *fc;
    int ret;
    --- a/include/linux/fs_context.h
    +++ b/include/linux/fs_context.h
    @@ -142,6 +142,8 @@ extern void put_fs_context(struct fs_con
    extern int vfs_parse_fs_param_source(struct fs_context *fc,
    struct fs_parameter *param);
    extern void fc_drop_locked(struct fs_context *fc);
    +int reconfigure_single(struct super_block *s,
    + int flags, void *data);

    /*
    * sget() wrappers to be called from the ->get_tree() op.

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