On Tue, 22 Jul 2025, Jeff Layton wrote:
> 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@xxxxxxxxxx>
> > ---
> > 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.
Maybe... an ERR_PTR-safe done_dentry_lookup() implies that you generally
don't need to unlock if you have an error. But that isn't the case
until this patch.
But it is only a one-patch gap if I introduce that a bit earlier. Maybe
it doesn't matter.
I'll try it and see what I think.
Thanks,
NeilBrown
>
> > }
> > 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@xxxxxxxxxx>
>
