From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F33D4345757; Wed, 12 Nov 2025 14:46:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762958793; cv=none; b=Hkbl/5VMPuuKSD0BcbG74ZqWOOQwzXt8DL+R1SWsssvH4y998GljXUWko/4Xgupd5IEzcRHa7CWKqHKV17Sc9siHCgs0X6BIDiBHQXW18kIfmm2NdYI4EdFZDFNiNl3xQALnYMUhQxAd611BHUQsbd+8S+L4Ojra917XrIDb/Fs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762958793; c=relaxed/simple; bh=W09oq+HYxVgVN/kosChQDcZ+ebdWtAbR+9uFU7ZwbLc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=QT7hXbcgd7Iget85biBwR1ENfTXqV5goRml2q88sW+FDNZBPs8lpTGXG6TQsPqXKppFBQYXf+JN91bbGaYnnZR/XXWO9LguiHau+wonBqkokxDXjSlcsJnChmgZVOrFTx1mBgK5uPVVYqJBWF6J9BQuXnrC5VTP039U1Vble1dY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=daaqerkF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="daaqerkF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8509AC4CEF5; Wed, 12 Nov 2025 14:46:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762958791; bh=W09oq+HYxVgVN/kosChQDcZ+ebdWtAbR+9uFU7ZwbLc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=daaqerkF6xj5TaEr/77ce8B3DNX8JX+Dus7t1apkIl0GhPUei/291tbqIexB+BB0p /KyoISnE0t4xdRZpcMs2CoZOiudDrK3GHCcgq2yTHfzHeln2cpGxm/+npJ6AOX/yDA opHo54wDKao8o8/BwHwKA3SJkdsD2N/5bCmm21v7zgrRNps5sj4UsJ5U7rhh1VrE0R +GPXdxqc/Y7ui4Bh0kd0DS1ZceyVKxs4UX2f9XcTV6++mn1yYXr9t9x7Ng0VW3r09u A7YTdwC64Tkume+ZmW0WRawFCOwySmDmjGb7G3zZJRsCWEL9ZZ5m6Gc+U8yWq8ble0 ys72mKLOArnPg== Message-ID: <32e65149e7678ac3cbc7f8dbed26429fd9c7ae78.camel@kernel.org> Subject: Re: [PATCH v5 02/14] VFS: introduce start_dirop() and end_dirop() From: Jeff Layton To: NeilBrown , Alexander Viro , Christian Brauner , Amir Goldstein Cc: Jan Kara , linux-fsdevel@vger.kernel.org, Chris Mason , David Sterba , David Howells , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , Tyler Hicks , Miklos Szeredi , Chuck Lever , Olga Kornievskaia , Dai Ngo , Namjae Jeon , Steve French , Sergey Senozhatsky , Carlos Maiolino , John Johansen , Paul Moore , James Morris , "Serge E. Hallyn" , Stephen Smalley , Ondrej Mosnacek , Mateusz Guzik , Lorenzo Stoakes , Stefan Berger , "Darrick J. Wong" , linux-kernel@vger.kernel.org, netfs@lists.linux.dev, ecryptfs@vger.kernel.org, linux-nfs@vger.kernel.org, linux-unionfs@vger.kernel.org, linux-cifs@vger.kernel.org, linux-xfs@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org Date: Wed, 12 Nov 2025 09:46:27 -0500 In-Reply-To: <20251106005333.956321-3-neilb@ownmail.net> References: <20251106005333.956321-1-neilb@ownmail.net> <20251106005333.956321-3-neilb@ownmail.net> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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DfX/sn9XcfoVZIxMpCRE750zvJvcCUz9HojsrMQ1NFc7MFT1z3MOW2/RlzPcog7xvR5ENPH19ojRD CHqumUHRry+RF0lH00clzX/W8OrQJZtoBPXv9ahka/Vp7kEulcBJr1cH5Wz/WprhsIM7U9pse1f1g Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.1 (3.58.1-1.fc43) Precedence: bulk X-Mailing-List: netfs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2025-11-06 at 11:50 +1100, NeilBrown wrote: > From: NeilBrown >=20 > The fact that directory operations (create,remove,rename) are protected > by a lock on the parent is known widely throughout the kernel. > In order to change this - to instead lock the target dentry - it is > best to centralise this knowledge so it can be changed in one place. >=20 > This patch introduces start_dirop() which is local to VFS code. > It performs the required locking for create and remove. Rename > will be handled separately. >=20 > Various functions with names like start_creating() or start_removing_path= (), > some of which already exist, will export this functionality beyond the VF= S. >=20 > end_dirop() is the partner of start_dirop(). It drops the lock and > releases the reference on the dentry. > It *is* exported so that various end_creating etc functions can be inline= . >=20 > As vfs_mkdir() drops the dentry on error we cannot use end_dirop() as > that won't unlock when the dentry IS_ERR(). For now we need an explicit > unlock when dentry IS_ERR(). I hope to change vfs_mkdir() to unlock > when it drops a dentry so that explicit unlock can go away. >=20 > end_dirop() can always be called on the result of start_dirop(), but not > after vfs_mkdir(). After a vfs_mkdir() we still may need the explicit > unlock as seen in end_creating_path(). >=20 > As well as adding start_dirop() and end_dirop() > this patch uses them in: > - simple_start_creating (which requires sharing lookup_noperm_common() > with libfs.c) > - start_removing_path / start_removing_user_path_at > - filename_create / end_creating_path() > - do_rmdir(), do_unlinkat() >=20 > Reviewed-by: Amir Goldstein > Signed-off-by: NeilBrown > --- > fs/internal.h | 3 ++ > fs/libfs.c | 36 ++++++++--------- > fs/namei.c | 98 ++++++++++++++++++++++++++++++++++------------ > include/linux/fs.h | 2 + > 4 files changed, 95 insertions(+), 44 deletions(-) >=20 > diff --git a/fs/internal.h b/fs/internal.h > index 9b2b4d116880..d08d5e2235e9 100644 > --- a/fs/internal.h > +++ b/fs/internal.h > @@ -67,6 +67,9 @@ int vfs_tmpfile(struct mnt_idmap *idmap, > const struct path *parentpath, > struct file *file, umode_t mode); > struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *); > +struct dentry *start_dirop(struct dentry *parent, struct qstr *name, > + unsigned int lookup_flags); > +int lookup_noperm_common(struct qstr *qname, struct dentry *base); > =20 > /* > * namespace.c > diff --git a/fs/libfs.c b/fs/libfs.c > index 1661dcb7d983..2d6657947abd 100644 > --- a/fs/libfs.c > +++ b/fs/libfs.c > @@ -2290,27 +2290,25 @@ void stashed_dentry_prune(struct dentry *dentry) > cmpxchg(stashed, dentry, NULL); > } > =20 > -/* parent must be held exclusive */ > +/** > + * simple_start_creating - prepare to create a given name > + * @parent: directory in which to prepare to create the name > + * @name: the name to be created > + * > + * Required lock is taken and a lookup in performed prior to creating an > + * object in a directory. No permission checking is performed. > + * > + * Returns: a negative dentry on which vfs_create() or similar may > + * be attempted, or an error. > + */ > struct dentry *simple_start_creating(struct dentry *parent, const char *= name) > { > - struct dentry *dentry; > - struct inode *dir =3D d_inode(parent); > + struct qstr qname =3D QSTR(name); > + int err; > =20 > - inode_lock(dir); > - if (unlikely(IS_DEADDIR(dir))) { > - inode_unlock(dir); > - return ERR_PTR(-ENOENT); > - } > - dentry =3D lookup_noperm(&QSTR(name), parent); > - if (IS_ERR(dentry)) { > - inode_unlock(dir); > - return dentry; > - } > - if (dentry->d_inode) { > - dput(dentry); > - inode_unlock(dir); > - return ERR_PTR(-EEXIST); > - } > - return dentry; > + err =3D lookup_noperm_common(&qname, parent); > + if (err) > + return ERR_PTR(err); > + return start_dirop(parent, &qname, LOOKUP_CREATE | LOOKUP_EXCL); > } > EXPORT_SYMBOL(simple_start_creating); > diff --git a/fs/namei.c b/fs/namei.c > index 39c4d52f5b54..231e1ffd4b8d 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -2765,6 +2765,48 @@ static int filename_parentat(int dfd, struct filen= ame *name, > return __filename_parentat(dfd, name, flags, parent, last, type, NULL); > } > =20 > +/** > + * start_dirop - begin a create or remove dirop, performing locking and = lookup > + * @parent: the dentry of the parent in which the operation will o= ccur > + * @name: a qstr holding the name within that parent > + * @lookup_flags: intent and other lookup flags. > + * > + * The lookup is performed and necessary locks are taken so that, on suc= cess, > + * the returned dentry can be operated on safely. > + * The qstr must already have the hash value calculated. > + * > + * Returns: a locked dentry, or an error. > + * > + */ > +struct dentry *start_dirop(struct dentry *parent, struct qstr *name, > + unsigned int lookup_flags) > +{ > + struct dentry *dentry; > + struct inode *dir =3D d_inode(parent); > + > + inode_lock_nested(dir, I_MUTEX_PARENT); > + dentry =3D lookup_one_qstr_excl(name, parent, lookup_flags); > + if (IS_ERR(dentry)) > + inode_unlock(dir); > + return dentry; > +} > + > +/** > + * end_dirop - signal completion of a dirop > + * @de: the dentry which was returned by start_dirop or similar. > + * > + * If the de is an error, nothing happens. Otherwise any lock taken to > + * protect the dentry is dropped and the dentry itself is release (dput(= )). > + */ > +void end_dirop(struct dentry *de) > +{ > + if (!IS_ERR(de)) { > + inode_unlock(de->d_parent->d_inode); > + dput(de); > + } > +} > +EXPORT_SYMBOL(end_dirop); > + > /* does lookup, returns the object with parent locked */ > static struct dentry *__start_removing_path(int dfd, struct filename *na= me, > struct path *path) > @@ -2781,10 +2823,9 @@ static struct dentry *__start_removing_path(int df= d, struct filename *name, > return ERR_PTR(-EINVAL); > /* don't fail immediately if it's r/o, at least try to report other err= ors */ > error =3D mnt_want_write(parent_path.mnt); > - inode_lock_nested(parent_path.dentry->d_inode, I_MUTEX_PARENT); > - d =3D lookup_one_qstr_excl(&last, parent_path.dentry, 0); > + d =3D start_dirop(parent_path.dentry, &last, 0); > if (IS_ERR(d)) > - goto unlock; > + goto drop; > if (error) > goto fail; > path->dentry =3D no_free_ptr(parent_path.dentry); > @@ -2792,10 +2833,9 @@ static struct dentry *__start_removing_path(int df= d, struct filename *name, > return d; > =20 > fail: > - dput(d); > + end_dirop(d); > d =3D ERR_PTR(error); > -unlock: > - inode_unlock(parent_path.dentry->d_inode); > +drop: > if (!error) > mnt_drop_write(parent_path.mnt); > return d; > @@ -2910,7 +2950,7 @@ int vfs_path_lookup(struct dentry *dentry, struct v= fsmount *mnt, > } > EXPORT_SYMBOL(vfs_path_lookup); > =20 > -static int lookup_noperm_common(struct qstr *qname, struct dentry *base) > +int lookup_noperm_common(struct qstr *qname, struct dentry *base) > { > const char *name =3D qname->name; > u32 len =3D qname->len; > @@ -4223,21 +4263,18 @@ static struct dentry *filename_create(int dfd, st= ruct filename *name, > */ > if (last.name[last.len] && !want_dir) > create_flags &=3D ~LOOKUP_CREATE; > - inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT); > - dentry =3D lookup_one_qstr_excl(&last, path->dentry, > - reval_flag | create_flags); > + dentry =3D start_dirop(path->dentry, &last, reval_flag | create_flags); > if (IS_ERR(dentry)) > - goto unlock; > + goto out_drop_write; > =20 > if (unlikely(error)) > goto fail; > =20 > return dentry; > fail: > - dput(dentry); > + end_dirop(dentry); > dentry =3D ERR_PTR(error); > -unlock: > - inode_unlock(path->dentry->d_inode); > +out_drop_write: > if (!error) > mnt_drop_write(path->mnt); > out: > @@ -4256,11 +4293,26 @@ struct dentry *start_creating_path(int dfd, const= char *pathname, > } > EXPORT_SYMBOL(start_creating_path); > =20 > +/** > + * end_creating_path - finish a code section started by start_creating_p= ath() > + * @path: the path instantiated by start_creating_path() > + * @dentry: the dentry returned by start_creating_path() > + * > + * end_creating_path() will unlock and locks taken by start_creating_pat= h() > + * and drop an references that were taken. It should only be called > + * if start_creating_path() returned a non-error. > + * If vfs_mkdir() was called and it returned an error, that error *shoul= d* > + * be passed to end_creating_path() together with the path. > + */ > void end_creating_path(const struct path *path, struct dentry *dentry) > { > - if (!IS_ERR(dentry)) > - dput(dentry); > - inode_unlock(path->dentry->d_inode); > + if (IS_ERR(dentry)) > + /* The parent is still locked despite the error from > + * vfs_mkdir() - must unlock it. > + */ > + inode_unlock(path->dentry->d_inode); > + else > + end_dirop(dentry); > mnt_drop_write(path->mnt); > path_put(path); > } > @@ -4592,8 +4644,7 @@ int do_rmdir(int dfd, struct filename *name) > if (error) > goto exit2; > =20 > - inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT); > - dentry =3D lookup_one_qstr_excl(&last, path.dentry, lookup_flags); > + dentry =3D start_dirop(path.dentry, &last, lookup_flags); > error =3D PTR_ERR(dentry); > if (IS_ERR(dentry)) > goto exit3; > @@ -4602,9 +4653,8 @@ int do_rmdir(int dfd, struct filename *name) > goto exit4; > error =3D vfs_rmdir(mnt_idmap(path.mnt), path.dentry->d_inode, dentry); > exit4: > - dput(dentry); > + end_dirop(dentry); > exit3: > - inode_unlock(path.dentry->d_inode); > mnt_drop_write(path.mnt); > exit2: > path_put(&path); > @@ -4721,8 +4771,7 @@ int do_unlinkat(int dfd, struct filename *name) > if (error) > goto exit2; > retry_deleg: > - inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT); > - dentry =3D lookup_one_qstr_excl(&last, path.dentry, lookup_flags); > + dentry =3D start_dirop(path.dentry, &last, lookup_flags); > error =3D PTR_ERR(dentry); > if (!IS_ERR(dentry)) { > =20 > @@ -4737,9 +4786,8 @@ int do_unlinkat(int dfd, struct filename *name) > error =3D vfs_unlink(mnt_idmap(path.mnt), path.dentry->d_inode, > dentry, &delegated_inode); > exit3: > - dput(dentry); > + end_dirop(dentry); > } > - inode_unlock(path.dentry->d_inode); > if (inode) > iput(inode); /* truncate the inode here */ > inode =3D NULL; > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 03e450dd5211..9e7556e79d19 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -3196,6 +3196,8 @@ extern void iterate_supers_type(struct file_system_= type *, > void filesystems_freeze(void); > void filesystems_thaw(void); > =20 > +void end_dirop(struct dentry *de); > + > extern int dcache_dir_open(struct inode *, struct file *); > extern int dcache_dir_close(struct inode *, struct file *); > extern loff_t dcache_dir_lseek(struct file *, loff_t, int); Reviewed-by: Jeff Layton