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fuse: Call vfs_get_tree() for submounts
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We recently fixed an infinite loop by setting the SB_BORN flag on
submounts along with the write barrier needed by super_cache_count().
This is the job of vfs_get_tree() and FUSE shouldn't have to care
about the barrier at all.

Split out some code from fuse_dentry_automount() to the dedicated
fuse_get_tree_submount() handler for submounts and call vfs_get_tree().

Signed-off-by: Greg Kurz <[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>
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gkurz authored and Miklos Szeredi committed Jun 22, 2021
1 parent fe0a7bd commit 266eb3f
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Showing 2 changed files with 41 additions and 48 deletions.
53 changes: 5 additions & 48 deletions fs/fuse/dir.c
Original file line number Diff line number Diff line change
Expand Up @@ -309,12 +309,8 @@ static int fuse_dentry_delete(const struct dentry *dentry)
static struct vfsmount *fuse_dentry_automount(struct path *path)
{
struct fs_context *fsc;
struct fuse_mount *parent_fm = get_fuse_mount_super(path->mnt->mnt_sb);
struct fuse_conn *fc = parent_fm->fc;
struct fuse_mount *fm;
struct vfsmount *mnt;
struct fuse_inode *mp_fi = get_fuse_inode(d_inode(path->dentry));
struct super_block *sb;
int err;

fsc = fs_context_for_submount(path->mnt->mnt_sb->s_type, path->dentry);
Expand All @@ -323,48 +319,15 @@ static struct vfsmount *fuse_dentry_automount(struct path *path)
goto out;
}

err = -ENOMEM;
fm = kzalloc(sizeof(struct fuse_mount), GFP_KERNEL);
if (!fm)
goto out_put_fsc;
/* Pass the FUSE inode of the mount for fuse_get_tree_submount() */
fsc->fs_private = mp_fi;

fsc->s_fs_info = fm;
sb = sget_fc(fsc, NULL, set_anon_super_fc);
if (IS_ERR(sb)) {
err = PTR_ERR(sb);
kfree(fm);
err = vfs_get_tree(fsc);
if (err)
goto out_put_fsc;
}
fm->fc = fuse_conn_get(fc);

/* Initialize superblock, making @mp_fi its root */
err = fuse_fill_super_submount(sb, mp_fi);
if (err) {
fuse_conn_put(fc);
kfree(fm);
sb->s_fs_info = NULL;
goto out_put_sb;
}

down_write(&fc->killsb);
list_add_tail(&fm->fc_entry, &fc->mounts);
up_write(&fc->killsb);

sb->s_flags |= SB_ACTIVE;
fsc->root = dget(sb->s_root);

/*
* FIXME: setting SB_BORN requires a write barrier for
* super_cache_count(). We should actually come
* up with a proper ->get_tree() implementation
* for submounts and call vfs_get_tree() to take
* care of the write barrier.
*/
smp_wmb();
sb->s_flags |= SB_BORN;

/* We are done configuring the superblock, so unlock it */
up_write(&sb->s_umount);
up_write(&fsc->root->d_sb->s_umount);

/* Create the submount */
mnt = vfs_create_mount(fsc);
Expand All @@ -376,12 +339,6 @@ static struct vfsmount *fuse_dentry_automount(struct path *path)
put_fs_context(fsc);
return mnt;

out_put_sb:
/*
* Only jump here when fsc->root is NULL and sb is still locked
* (otherwise put_fs_context() will put the superblock)
*/
deactivate_locked_super(sb);
out_put_fsc:
put_fs_context(fsc);
out:
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36 changes: 36 additions & 0 deletions fs/fuse/inode.c
Original file line number Diff line number Diff line change
Expand Up @@ -1353,8 +1353,44 @@ int fuse_fill_super_submount(struct super_block *sb,
return 0;
}

/* Filesystem context private data holds the FUSE inode of the mount point */
static int fuse_get_tree_submount(struct fs_context *fsc)
{
struct fuse_mount *fm;
struct fuse_inode *mp_fi = fsc->fs_private;
struct fuse_conn *fc = get_fuse_conn(&mp_fi->inode);
struct super_block *sb;
int err;

fm = kzalloc(sizeof(struct fuse_mount), GFP_KERNEL);
if (!fm)
return -ENOMEM;

fsc->s_fs_info = fm;
sb = sget_fc(fsc, NULL, set_anon_super_fc);
if (IS_ERR(sb)) {
kfree(fm);
return PTR_ERR(sb);
}
fm->fc = fuse_conn_get(fc);

/* Initialize superblock, making @mp_fi its root */
err = fuse_fill_super_submount(sb, mp_fi);
if (err) {
fuse_conn_put(fc);
kfree(fm);
sb->s_fs_info = NULL;
deactivate_locked_super(sb);
return err;
}

down_write(&fc->killsb);
list_add_tail(&fm->fc_entry, &fc->mounts);
up_write(&fc->killsb);

sb->s_flags |= SB_ACTIVE;
fsc->root = dget(sb->s_root);

return 0;
}

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