On Mon 05-05-25 22:38:29, Al Viro wrote:
> On Mon, May 05, 2025 at 12:55:34PM +0200, Jan Kara wrote:
> > > if (!type)
> > > return NULL;
> > > - mnt = vfs_submount(mntpt, type, "tracefs", NULL);
> > > +
> > > + fc = fs_context_for_submount(type, mntpt);
> > > + if (IS_ERR(fc))
> > > + return ERR_CAST(fc);
> >
> > Missing put_filesystem() here?
>
> Actually, I'd rather have it done unconditionally right after
> fc_context_for_submount() - fs_context allocation grabs
> a reference and it's held until put_fs_context, so...
>
> [PATCH] kill vfs_submount()
>
> The last remaining user of vfs_submount() (tracefs) is easy to convert
> to fs_context_for_submount(); do that and bury that thing, along with
> SB_SUBMOUNT
>
> Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Indeed this works as well. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 018e95fe5459..0577a9fb6050 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -1329,21 +1329,6 @@ struct vfsmount *vfs_kern_mount(struct file_system_type *type,
> }
> EXPORT_SYMBOL_GPL(vfs_kern_mount);
>
> -struct vfsmount *
> -vfs_submount(const struct dentry *mountpoint, struct file_system_type *type,
> - const char *name, void *data)
> -{
> - /* Until it is worked out how to pass the user namespace
> - * through from the parent mount to the submount don't support
> - * unprivileged mounts with submounts.
> - */
> - if (mountpoint->d_sb->s_user_ns != &init_user_ns)
> - return ERR_PTR(-EPERM);
> -
> - return vfs_kern_mount(type, SB_SUBMOUNT, name, data);
> -}
> -EXPORT_SYMBOL_GPL(vfs_submount);
> -
> static struct mount *clone_mnt(struct mount *old, struct dentry *root,
> int flag)
> {
> diff --git a/fs/super.c b/fs/super.c
> index 97a17f9d9023..1886e4c930e0 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -823,13 +823,6 @@ struct super_block *sget(struct file_system_type *type,
> struct super_block *old;
> int err;
>
> - /* We don't yet pass the user namespace of the parent
> - * mount through to here so always use &init_user_ns
> - * until that changes.
> - */
> - if (flags & SB_SUBMOUNT)
> - user_ns = &init_user_ns;
> -
> retry:
> spin_lock(&sb_lock);
> if (test) {
> @@ -849,7 +842,7 @@ struct super_block *sget(struct file_system_type *type,
> }
> if (!s) {
> spin_unlock(&sb_lock);
> - s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
> + s = alloc_super(type, flags, user_ns);
> if (!s)
> return ERR_PTR(-ENOMEM);
> goto retry;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 016b0fe1536e..515e702d98ae 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1240,7 +1240,6 @@ extern int send_sigurg(struct file *file);
> /* These sb flags are internal to the kernel */
> #define SB_DEAD BIT(21)
> #define SB_DYING BIT(24)
> -#define SB_SUBMOUNT BIT(26)
> #define SB_FORCE BIT(27)
> #define SB_NOSEC BIT(28)
> #define SB_BORN BIT(29)
> diff --git a/include/linux/mount.h b/include/linux/mount.h
> index dcc17ce8a959..d4eb90a367af 100644
> --- a/include/linux/mount.h
> +++ b/include/linux/mount.h
> @@ -98,9 +98,6 @@ extern struct vfsmount *vfs_create_mount(struct fs_context *fc);
> extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
> int flags, const char *name,
> void *data);
> -extern struct vfsmount *vfs_submount(const struct dentry *mountpoint,
> - struct file_system_type *type,
> - const char *name, void *data);
>
> extern void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list);
> extern void mark_mounts_for_expiry(struct list_head *mounts);
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index e22aacb0028a..936a615e8c56 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -51,6 +51,7 @@
> #include <linux/workqueue.h>
> #include <linux/sort.h>
> #include <linux/io.h> /* vmap_page_range() */
> +#include <linux/fs_context.h>
>
> #include <asm/setup.h> /* COMMAND_LINE_SIZE */
>
> @@ -10075,6 +10076,8 @@ static struct vfsmount *trace_automount(struct dentry *mntpt, void *ingore)
> {
> struct vfsmount *mnt;
> struct file_system_type *type;
> + struct fs_context *fc;
> + int ret;
>
> /*
> * To maintain backward compatibility for tools that mount
> @@ -10084,10 +10087,20 @@ static struct vfsmount *trace_automount(struct dentry *mntpt, void *ingore)
> type = get_fs_type("tracefs");
> if (!type)
> return NULL;
> - mnt = vfs_submount(mntpt, type, "tracefs", NULL);
> +
> + fc = fs_context_for_submount(type, mntpt);
> put_filesystem(type);
> - if (IS_ERR(mnt))
> - return NULL;
> + if (IS_ERR(fc))
> + return ERR_CAST(fc);
> +
> + ret = vfs_parse_fs_string(fc, "source",
> + "tracefs", strlen("tracefs"));
> + if (!ret)
> + mnt = fc_mount(fc);
> + else
> + mnt = ERR_PTR(ret);
> +
> + put_fs_context(fc);
> return mnt;
> }
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
