[PATCH v5 05/14] VFS/nfsd/cachefiles/ovl: introduce start_removing() and end_removing()

NeilBrown
2025-11-06T00:55:05Z

From: NeilBrown <neil@brown.name>

start_removing() is similar to start_creating() but will only return a
positive dentry with the expectation that it will be removed. This is
used by nfsd, cachefiles, and overlayfs. They are changed to also use
end_removing() to terminate the action begun by start_removing(). This
is a simple alias for end_dirop().

Apart from changes to the error paths, as we no longer need to unlock on
a lookup error, an effect on callers is that they don't need to test if
the found dentry is positive or negative - they can be sure it is
positive.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: NeilBrown <neil@brown.name>
---
fs/cachefiles/namei.c | 32 ++++++++++++++------------------
fs/namei.c | 27 +++++++++++++++++++++++++++
fs/nfsd/nfs4recover.c | 18 +++++-------------
fs/nfsd/vfs.c | 26 ++++++++++----------------
fs/overlayfs/dir.c | 15 +++++++--------
fs/overlayfs/overlayfs.h | 8 ++++++++
include/linux/namei.h | 18 ++++++++++++++++++
7 files changed, 89 insertions(+), 55 deletions(-)

diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index 0a136eb434da..c7f0c6ab9b88 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -260,6 +260,7 @@ static int cachefiles_unlink(struct cachefiles_cache *cache,
* - File backed objects are unlinked
* - Directory backed objects are stuffed into the graveyard for userspace to
* delete
+ * On entry dir must be locked. It will be unlocked on exit.
*/
int cachefiles_bury_object(struct cachefiles_cache *cache,
struct cachefiles_object *object,
@@ -274,28 +275,30 @@ int cachefiles_bury_object(struct cachefiles_cache *cache,

_enter(",'%pd','%pd'", dir, rep);

+ /* end_removing() will dput() @rep but we need to keep
+ * a ref, so take one now. This also stops the dentry
+ * being negated when unlinked which we need.
+ */
+ dget(rep);
+
if (rep->d_parent != dir) {
- inode_unlock(d_inode(dir));
+ end_removing(rep);
_leave(" = -ESTALE");
return -ESTALE;
}

/* non-directories can just be unlinked */
if (!d_is_dir(rep)) {
- dget(rep); /* Stop the dentry being negated if it's only pinned
- * by a file struct.
- */
ret = cachefiles_unlink(cache, object, dir, rep, why);
- dput(rep);
+ end_removing(rep);

- inode_unlock(d_inode(dir));
_leave(" = %d", ret);
return ret;
}

/* directories have to be moved to the graveyard */
_debug("move stale object to graveyard");
- inode_unlock(d_inode(dir));
+ end_removing(rep);

try_again:
/* first step is to make up a grave dentry in the graveyard */
@@ -749,26 +752,20 @@ static struct dentry *cachefiles_lookup_for_cull(struct cachefiles_cache *cache,
struct dentry *victim;
int ret = -ENOENT;

- inode_lock_nested(d_inode(dir), I_MUTEX_PARENT);
+ victim = start_removing(&nop_mnt_idmap, dir, &QSTR(filename));

- victim = lookup_one(&nop_mnt_idmap, &QSTR(filename), dir);
if (IS_ERR(victim))
goto lookup_error;
- if (d_is_negative(victim))
- goto lookup_put;
if (d_inode(victim)->i_flags & S_KERNEL_FILE)
goto lookup_busy;
return victim;

lookup_busy:
ret = -EBUSY;
-lookup_put:
- inode_unlock(d_inode(dir));
- dput(victim);
+ end_removing(victim);
return ERR_PTR(ret);

lookup_error:
- inode_unlock(d_inode(dir));
ret = PTR_ERR(victim);
if (ret == -ENOENT)
return ERR_PTR(-ESTALE); /* Probably got retired by the netfs */
@@ -816,18 +813,17 @@ int cachefiles_cull(struct cachefiles_cache *cache, struct dentry *dir,

ret = cachefiles_bury_object(cache, NULL, dir, victim,
FSCACHE_OBJECT_WAS_CULLED);
+ dput(victim);
if (ret < 0)
goto error;

fscache_count_culled();
- dput(victim);
_leave(" = 0");
return 0;

error_unlock:
- inode_unlock(d_inode(dir));
+ end_removing(victim);
error:
- dput(victim);
if (ret == -ENOENT)
return -ESTALE; /* Probably got retired by the netfs */

diff --git a/fs/namei.c b/fs/namei.c
index 8873ad0f05b0..38dda29552f6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3248,6 +3248,33 @@ struct dentry *start_creating(struct mnt_idmap *idmap, struct dentry *parent,
}
EXPORT_SYMBOL(start_creating);

+/**
+ * start_removing - prepare to remove a given name with permission checking
+ * @idmap: idmap of the mount
+ * @parent: directory in which to find the name
+ * @name: the name to be removed
+ *
+ * Locks are taken and a lookup in performed prior to removing
+ * an object from a directory. Permission checking (MAY_EXEC) is performed
+ * against @idmap.
+ *
+ * If the name doesn't exist, an error is returned.
+ *
+ * end_removing() should be called when removal is complete, or aborted.
+ *
+ * Returns: a positive dentry, or an error.
+ */
+struct dentry *start_removing(struct mnt_idmap *idmap, struct dentry *parent,
+ struct qstr *name)
+{
+ int err = lookup_one_common(idmap, name, parent);
+
+ if (err)
+ return ERR_PTR(err);
+ return start_dirop(parent, name, 0);
+}
+EXPORT_SYMBOL(start_removing);
+
#ifdef CONFIG_UNIX98_PTYS
int path_pts(struct path *path)
{
diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index c247a7c3291c..3eefaa2202e3 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -324,20 +324,12 @@ nfsd4_unlink_clid_dir(char *name, struct nfsd_net *nn)
dprintk("NFSD: nfsd4_unlink_clid_dir. name %s\n", name);

dir = nn->rec_file->f_path.dentry;
- inode_lock_nested(d_inode(dir), I_MUTEX_PARENT);
- dentry = lookup_one(&nop_mnt_idmap, &QSTR(name), dir);
- if (IS_ERR(dentry)) {
- status = PTR_ERR(dentry);
- goto out_unlock;
- }
- status = -ENOENT;
- if (d_really_is_negative(dentry))
- goto out;
+ dentry = start_removing(&nop_mnt_idmap, dir, &QSTR(name));
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+
status = vfs_rmdir(&nop_mnt_idmap, d_inode(dir), dentry);
-out:
- dput(dentry);
-out_unlock:
- inode_unlock(d_inode(dir));
+ end_removing(dentry);
return status;
}

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 24e501abad0e..6291c371caa7 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -2044,7 +2044,7 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
{
struct dentry *dentry, *rdentry;
struct inode *dirp;
- struct inode *rinode;
+ struct inode *rinode = NULL;
__be32 err;
int host_err;

@@ -2063,24 +2063,21 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,

dentry = fhp->fh_dentry;
dirp = d_inode(dentry);
- inode_lock_nested(dirp, I_MUTEX_PARENT);

- rdentry = lookup_one(&nop_mnt_idmap, &QSTR_LEN(fname, flen), dentry);
+ rdentry = start_removing(&nop_mnt_idmap, dentry, &QSTR_LEN(fname, flen));
+
host_err = PTR_ERR(rdentry);
if (IS_ERR(rdentry))
- goto out_unlock;
+ goto out_drop_write;

- if (d_really_is_negative(rdentry)) {
- dput(rdentry);
- host_err = -ENOENT;
- goto out_unlock;
- }
- rinode = d_inode(rdentry);
err = fh_fill_pre_attrs(fhp);
if (err != nfs_ok)
goto out_unlock;

+ rinode = d_inode(rdentry);
+ /* Prevent truncation until after locks dropped */
ihold(rinode);
+
if (!type)
type = d_inode(rdentry)->i_mode & S_IFMT;

@@ -2102,10 +2099,10 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
}
fh_fill_post_attrs(fhp);

- inode_unlock(dirp);
- if (!host_err)
+out_unlock:
+ end_removing(rdentry);
+ if (!err && !host_err)
host_err = commit_metadata(fhp);
- dput(rdentry);
iput(rinode); /* truncate the inode here */

out_drop_write:
@@ -2123,9 +2120,6 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
}
out:
return err != nfs_ok ? err : nfserrno(host_err);
-out_unlock:
- inode_unlock(dirp);
- goto out_drop_write;
}

/*
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index b9160fefbd00..20682afdbd20 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -866,17 +866,17 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir,
goto out;
}

- inode_lock_nested(dir, I_MUTEX_PARENT);
- upper = ovl_lookup_upper(ofs, dentry->d_name.name, upperdir,
- dentry->d_name.len);
+ upper = ovl_start_removing_upper(ofs, upperdir,
+ &QSTR_LEN(dentry->d_name.name,
+ dentry->d_name.len));
err = PTR_ERR(upper);
if (IS_ERR(upper))
- goto out_unlock;
+ goto out_dput;

err = -ESTALE;
if ((opaquedir && upper != opaquedir) ||
(!opaquedir && !ovl_matches_upper(dentry, upper)))
- goto out_dput_upper;
+ goto out_unlock;

if (is_dir)
err = ovl_do_rmdir(ofs, dir, upper);
@@ -892,10 +892,9 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir,
*/
if (!err)
d_drop(dentry);
-out_dput_upper:
- dput(upper);
out_unlock:
- inode_unlock(dir);
+ end_removing(upper);
+out_dput:
dput(opaquedir);
out:
return err;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index beeba96cfcb2..49ad65f829dc 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -423,6 +423,14 @@ static inline struct dentry *ovl_start_creating_upper(struct ovl_fs *ofs,
parent, name);
}

+static inline struct dentry *ovl_start_removing_upper(struct ovl_fs *ofs,
+ struct dentry *parent,
+ struct qstr *name)
+{
+ return start_removing(ovl_upper_mnt_idmap(ofs),
+ parent, name);
+}
+
static inline bool ovl_open_flags_need_copy_up(int flags)
{
if (!flags)
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 37b72f4a64f0..6d1069f93ebf 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -91,6 +91,8 @@ struct dentry *lookup_one_positive_killable(struct mnt_idmap *idmap,

struct dentry *start_creating(struct mnt_idmap *idmap, struct dentry *parent,
struct qstr *name);
+struct dentry *start_removing(struct mnt_idmap *idmap, struct dentry *parent,
+ struct qstr *name);

/**
* end_creating - finish action started with start_creating
@@ -122,6 +124,22 @@ static inline void end_creating(struct dentry *child, struct dentry *parent)
end_dirop(child);
}

+/**
+ * end_removing - finish action started with start_removing
+ * @child: dentry returned by start_removing()
+ * @parent: dentry given to start_removing()
+ *
+ * Unlock and release the child.
+ *
+ * This is identical to end_dirop(). It can be passed the result of
+ * start_removing() whether that was successful or not, but it not needed
+ * if start_removing() failed.
+ */
+static inline void end_removing(struct dentry *child)
+{
+ end_dirop(child);
+}
+
extern int follow_down_one(struct path *);
extern int follow_down(struct path *path, unsigned int flags);
extern int follow_up(struct path *);
--
2.50.0.107.gf914562f5916.dirty