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Message-ID: <15970691ac14728701c4e94e91cb3614caf5b503.camel@kernel.org>
Date: Mon, 21 Jul 2025 10:46:04 -0400
From: Jeff Layton <jlayton@...nel.org>
To: NeilBrown <neil@...wn.name>, Linus Torvalds
<torvalds@...ux-foundation.org>, Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] VFS: Change vfs_mkdir() to unlock on failure.
On Mon, 2025-07-21 at 17:59 +1000, NeilBrown wrote:
> Proposed changes to directory-op locking will lock the dentry rather
> than the whole directory. So the dentry will need to be unlocked.
>
> vfs_mkdir() consumes the dentry on error, so there will be no dentry to
> be unlocked.
>
> So this patch changes vfs_mkdir() to unlock on error as well as
> releasing the dentry. This requires various other functions in various
> callers to also unlock on error.
>
> At present this results in some clumsy code. Once the transition to
> dentry locking is complete the clumsiness will be gone.
>
> Signed-off-by: NeilBrown <neil@...wn.name>
> ---
> fs/cachefiles/namei.c | 9 +++++----
> fs/ecryptfs/inode.c | 3 ++-
> fs/namei.c | 24 ++++++++++++++++--------
> fs/nfsd/nfs4recover.c | 12 +++++-------
> fs/nfsd/vfs.c | 12 ++++++++++--
> fs/overlayfs/dir.c | 13 +++++++------
> fs/overlayfs/overlayfs.h | 1 +
> fs/overlayfs/super.c | 5 +++--
> fs/xfs/scrub/orphanage.c | 2 +-
> 9 files changed, 50 insertions(+), 31 deletions(-)
>
> diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
> index d1edb2ac3837..732d78911bed 100644
> --- a/fs/cachefiles/namei.c
> +++ b/fs/cachefiles/namei.c
> @@ -131,8 +131,11 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
> ret = cachefiles_inject_write_error();
> if (ret == 0)
> subdir = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), subdir, 0700);
> - else
> + else {
> + /* vfs_mkdir() unlocks on failure so we must too */
> + inode_unlock(d_inode(dir));
> subdir = ERR_PTR(ret);
> + }
> if (IS_ERR(subdir)) {
> trace_cachefiles_vfs_error(NULL, d_inode(dir), ret,
> cachefiles_trace_mkdir_error);
> @@ -196,9 +199,7 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
> return ERR_PTR(-EBUSY);
>
> mkdir_error:
> - inode_unlock(d_inode(dir));
> - if (!IS_ERR(subdir))
> - dput(subdir);
> + done_dentry_lookup(subdir);
> pr_err("mkdir %s failed with error %d\n", dirname, ret);
> return ERR_PTR(ret);
>
> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> index abd954c6a14e..5d8cb042aa57 100644
> --- a/fs/ecryptfs/inode.c
> +++ b/fs/ecryptfs/inode.c
> @@ -520,7 +520,7 @@ static struct dentry *ecryptfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
> lower_dentry, mode);
> rc = PTR_ERR(lower_dentry);
> if (IS_ERR(lower_dentry))
> - goto out;
> + goto out_unlocked;
> rc = 0;
> if (d_unhashed(lower_dentry))
> goto out;
> @@ -532,6 +532,7 @@ static struct dentry *ecryptfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
> set_nlink(dir, lower_dir->i_nlink);
> out:
> inode_unlock(lower_dir);
> +out_unlocked:
> if (d_really_is_negative(dentry))
> d_drop(dentry);
> return ERR_PTR(rc);
> diff --git a/fs/namei.c b/fs/namei.c
> index da160a01e23d..950a0d0d54da 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1723,13 +1723,18 @@ EXPORT_SYMBOL(lookup_one_qstr_excl);
> * rmdir) a dentry. After this, done_dentry_lookup() can be used to both
> * unlock the parent directory and dput() the dentry.
> *
> + * If the dentry is an error - as can happen after vfs_mkdir() -
> + * the unlock is skipped as unneeded.
> + *
> * This interface allows a smooth transition from parent-dir based
> * locking to dentry based locking.
> */
> void done_dentry_lookup(struct dentry *dentry)
> {
> - inode_unlock(dentry->d_parent->d_inode);
> - dput(dentry);
> + if (!IS_ERR(dentry)) {
> + inode_unlock(dentry->d_parent->d_inode);
> + dput(dentry);
> + }
nit: could you introduce these versions of done_dentry_lookup() and
done_dentry_lookup_return() in patch #2, even if not strictly needed
yet? Better to introduce it as ERR_PTR-safe from the start.
> }
> EXPORT_SYMBOL(done_dentry_lookup);
>
> @@ -1742,12 +1747,16 @@ EXPORT_SYMBOL(done_dentry_lookup);
> * rmdir) a dentry. After this, done_dentry_lookup_return() can be used to
> * unlock the parent directory. The dentry is returned for further use.
> *
> + * If the dentry is an error - as can happen after vfs_mkdir() -
> + * the unlock is skipped as unneeded.
> + *
> * This interface allows a smooth transition from parent-dir based
> * locking to dentry based locking.
> */
> struct dentry *done_dentry_lookup_return(struct dentry *dentry)
> {
> - inode_unlock(dentry->d_parent->d_inode);
> + if (!IS_ERR(dentry))
> + inode_unlock(dentry->d_parent->d_inode);
> return dentry;
> }
> EXPORT_SYMBOL(done_dentry_lookup_return);
> @@ -4210,9 +4219,7 @@ EXPORT_SYMBOL(kern_path_create);
>
> void done_path_create(struct path *path, struct dentry *dentry)
> {
> - if (!IS_ERR(dentry))
> - dput(dentry);
> - inode_unlock(path->dentry->d_inode);
> + done_dentry_lookup(dentry);
> mnt_drop_write(path->mnt);
> path_put(path);
> }
> @@ -4375,7 +4382,8 @@ SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, d
> * negative or unhashes it and possibly splices a different one returning it,
> * the original dentry is dput() and the alternate is returned.
> *
> - * In case of an error the dentry is dput() and an ERR_PTR() is returned.
> + * In case of an error the dentry is dput(), the parent is unlocked, and
> + * an ERR_PTR() is returned.
> */
> struct dentry *vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
> struct dentry *dentry, umode_t mode)
> @@ -4413,7 +4421,7 @@ struct dentry *vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
> return dentry;
>
> err:
> - dput(dentry);
> + done_dentry_lookup(dentry);
> return ERR_PTR(error);
> }
> EXPORT_SYMBOL(vfs_mkdir);
> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> index 82785db730d9..693fa95fa678 100644
> --- a/fs/nfsd/nfs4recover.c
> +++ b/fs/nfsd/nfs4recover.c
> @@ -222,7 +222,8 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
> dentry = lookup_one(&nop_mnt_idmap, &QSTR(dname), dir);
> if (IS_ERR(dentry)) {
> status = PTR_ERR(dentry);
> - goto out_unlock;
> + inode_unlock(d_inode(dir));
> + goto out;
> }
> if (d_really_is_positive(dentry))
> /*
> @@ -233,15 +234,12 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
> * In the 4.0 case, we should never get here; but we may
> * as well be forgiving and just succeed silently.
> */
> - goto out_put;
> + goto out;
> dentry = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), dentry, S_IRWXU);
> if (IS_ERR(dentry))
> status = PTR_ERR(dentry);
> -out_put:
> - if (!status)
> - dput(dentry);
> -out_unlock:
> - inode_unlock(d_inode(dir));
> +out:
> + done_dentry_lookup(dentry);
> if (status == 0) {
> if (nn->in_grace)
> __nfsd4_create_reclaim_record_grace(clp, dname,
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index a21940cadede..e85195e858a2 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1489,7 +1489,9 @@ nfsd_check_ignore_resizing(struct iattr *iap)
> iap->ia_valid &= ~ATTR_SIZE;
> }
>
> -/* The parent directory should already be locked: */
> +/* The parent directory should already be locked. The lock
> + * will be dropped on error.
> + */
> __be32
> nfsd_create_locked(struct svc_rqst *rqstp, struct svc_fh *fhp,
> struct nfsd_attrs *attrs,
> @@ -1555,8 +1557,11 @@ nfsd_create_locked(struct svc_rqst *rqstp, struct svc_fh *fhp,
> err = nfsd_create_setattr(rqstp, fhp, resfhp, attrs);
>
> out:
> - if (!IS_ERR(dchild))
> + if (!IS_ERR(dchild)) {
> + if (err)
> + inode_unlock(dirp);
> dput(dchild);
> + }
> return err;
>
> out_nfserr:
> @@ -1613,6 +1618,9 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> if (err != nfs_ok)
> goto out_unlock;
> err = nfsd_create_locked(rqstp, fhp, attrs, type, rdev, resfhp);
> + if (err)
> + /* lock will have been dropped */
> + return err;
> fh_fill_post_attrs(fhp);
> out_unlock:
> inode_unlock(dentry->d_inode);
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index 30619777f0f6..74b52595ea0e 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -161,14 +161,17 @@ int ovl_cleanup_and_whiteout(struct ovl_fs *ofs, struct dentry *dir,
> goto out;
> }
>
> +/* dir will be unlocked on return */
> struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent,
> struct dentry *newdentry, struct ovl_cattr *attr)
> {
> struct inode *dir = parent->d_inode;
> int err;
>
> - if (IS_ERR(newdentry))
> + if (IS_ERR(newdentry)) {
> + inode_unlock(dir);
> return newdentry;
> + }
>
> err = -ESTALE;
> if (newdentry->d_inode)
> @@ -213,11 +216,11 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent,
> }
> out:
> if (err) {
> - if (!IS_ERR(newdentry))
> - dput(newdentry);
> + done_dentry_lookup(newdentry);
> return ERR_PTR(err);
> + } else {
> + return done_dentry_lookup_return(newdentry);
> }
> - return newdentry;
> }
>
> struct dentry *ovl_create_temp(struct ovl_fs *ofs, struct dentry *workdir,
> @@ -227,7 +230,6 @@ struct dentry *ovl_create_temp(struct ovl_fs *ofs, struct dentry *workdir,
> inode_lock(workdir->d_inode);
> ret = ovl_create_real(ofs, workdir,
> ovl_lookup_temp(ofs, workdir), attr);
> - inode_unlock(workdir->d_inode);
> return ret;
> }
>
> @@ -335,7 +337,6 @@ static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
> ovl_lookup_upper(ofs, dentry->d_name.name,
> upperdir, dentry->d_name.len),
> attr);
> - inode_unlock(udir);
> if (IS_ERR(newdentry))
> return PTR_ERR(newdentry);
>
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 4f84abaa0d68..238c26142318 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -250,6 +250,7 @@ static inline struct dentry *ovl_do_mkdir(struct ovl_fs *ofs,
>
> ret = vfs_mkdir(ovl_upper_mnt_idmap(ofs), dir, dentry, mode);
> pr_debug("mkdir(%pd2, 0%o) = %i\n", dentry, mode, PTR_ERR_OR_ZERO(ret));
> + /* Note: dir will have been unlocked on failure */
> return ret;
> }
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 4afa91882075..df99a6fa17ef 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -328,11 +328,11 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> }
>
> work = ovl_do_mkdir(ofs, dir, work, attr.ia_mode);
> - inode_unlock(dir);
> err = PTR_ERR(work);
> if (IS_ERR(work))
> goto out_err;
>
> + done_dentry_lookup_return(work);
> /* Weird filesystem returning with hashed negative (kernfs)? */
> err = -EINVAL;
> if (d_really_is_negative(work))
> @@ -623,7 +623,8 @@ static struct dentry *ovl_lookup_or_create(struct ovl_fs *ofs,
> child = ovl_lookup_upper(ofs, name, parent, len);
> if (!IS_ERR(child) && !child->d_inode)
> child = ovl_create_real(ofs, parent, child, OVL_CATTR(mode));
> - inode_unlock(parent->d_inode);
> + else
> + inode_unlock(parent->d_inode);
> dput(parent);
>
> return child;
> diff --git a/fs/xfs/scrub/orphanage.c b/fs/xfs/scrub/orphanage.c
> index 9c12cb844231..c95bded4e8a7 100644
> --- a/fs/xfs/scrub/orphanage.c
> +++ b/fs/xfs/scrub/orphanage.c
> @@ -170,7 +170,7 @@ xrep_orphanage_create(
> orphanage_dentry, 0750);
> error = PTR_ERR(orphanage_dentry);
> if (IS_ERR(orphanage_dentry))
> - goto out_unlock_root;
> + goto out_dput_root;
> }
>
> /* Not a directory? Bail out. */
This does make for some awkward code. Fortunately there aren't that
many vfs_mkdir() callers.
--
Jeff Layton <jlayton@...nel.org>
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