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 0AA0B1EA7F1; Thu, 6 Feb 2025 13:50:01 +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=1738849802; cv=none; b=mujSIrRzke9BveY7PgWcoNMnLrS5vcJ5cM30h4uky7bXVhnvUD3km7x9gzdxpbek2U1RQTTs8dH6GHMUmLbO8U2tcZCcds2MdkCFF+v6UOWAD/FK4X74TgC/0QUwkIJ179xnEUb9tYgrZfar6YRayMzYohgYlP1sMAQxtcna6dY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738849802; c=relaxed/simple; bh=U/mvtnUPLU7Tk9UJIF1UndA8CJrBix59gciTuECRuDA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UgCS5mUGNz6zhsClG/ZjaNRE9KqmSfQIf4oefIUghJWBtA4viMrn/GjVTwuqU0HdCVStKdV3eTHdeeJYaPbK+6MphNEMcrmRT70idbr8KnJ7w33n0N3k/JfGRgMiZws2YjE+mYvLCAhBwmPvQjPIMvMg5UFOoLbP/MLELb2EWSw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YQOJi6/+; 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="YQOJi6/+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 00A4FC4CEDD; Thu, 6 Feb 2025 13:49:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738849801; bh=U/mvtnUPLU7Tk9UJIF1UndA8CJrBix59gciTuECRuDA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YQOJi6/+luPLqDEEHUL/+DGZfhe1V4FvE0ZmkZd0oqf50iuAPuUgaEB08M0qjAEW8 ceTDq4ig4vKf9Fsb2fjNfvBkscZTG1we3+MP+fNfIihtNRsOz5kcrZT9Fe6+xodnZw TZTTYvuuQYtli/hvJIkuKw+M6w5tGh6QP3cpChEoZGm+UkPpPRl3DiFUCePx3o2ZPp EF7noGEXBwufF6QpN3bkEQISLbVdaXtUp0KlZhZ6HadKuqOmx9umcH7nwaJxbbeRMM Y5WCfleR8imimX4qknX6S9WSnik2HYH626TxWr0S75byeQ/+TS/fjVVHQOOAV8lq1G zdh+yeA6yZ4VQ== Date: Thu, 6 Feb 2025 14:49:56 +0100 From: Christian Brauner To: NeilBrown Cc: Alexander Viro , Jan Kara , Linus Torvalds , Jeff Layton , Dave Chinner , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 08/19] VFS: introduce lookup_and_lock() and friends Message-ID: <20250206-herde-zunutze-2ad5be3fea78@brauner> References: <20250206054504.2950516-1-neilb@suse.de> <20250206054504.2950516-9-neilb@suse.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250206054504.2950516-9-neilb@suse.de> On Thu, Feb 06, 2025 at 04:42:45PM +1100, NeilBrown wrote: > lookup_and_lock() combines locking the directory and performing a lookup > prior to a change to the directory. > Abstracting this prepares for changing the locking requirements. > > done_lookup_and_lock() provides the inverse of putting the dentry and > unlocking. > > For "silly_rename" we will need to lookup_and_lock() in a directory that > is already locked. For this purpose we add LOOKUP_PARENT_LOCKED. > > Like lookup_len_qstr(), lookup_and_lock() returns -ENOENT if > LOOKUP_CREATE was NOT given and the name cannot be found,, and returns > -EEXIST if LOOKUP_EXCL WAS given and the name CAN be found. > > These functions replace all uses of lookup_one_qstr() in namei.c > except for those used for rename. > > The name might seem backwards as the lock happens before the lookup. > A future patch will change this so that only a shared lock is taken > before the lookup, and an exclusive lock on the dentry is taken after a > successful lookup. So the order "lookup" then "lock" will make sense. > > This functionality is exported as lookup_and_lock_one() which takes a > name and len rather than a qstr. > > Signed-off-by: NeilBrown > --- > fs/namei.c | 102 ++++++++++++++++++++++++++++-------------- > include/linux/namei.h | 15 ++++++- > 2 files changed, 83 insertions(+), 34 deletions(-) > > diff --git a/fs/namei.c b/fs/namei.c > index 69610047f6c6..3c0feca081a2 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -1715,6 +1715,41 @@ struct dentry *lookup_one_qstr(const struct qstr *name, > } > EXPORT_SYMBOL(lookup_one_qstr); > > +static struct dentry *lookup_and_lock_nested(const struct qstr *last, > + struct dentry *base, > + unsigned int lookup_flags, > + unsigned int subclass) > +{ > + struct dentry *dentry; > + > + if (!(lookup_flags & LOOKUP_PARENT_LOCKED)) > + inode_lock_nested(base->d_inode, subclass); > + > + dentry = lookup_one_qstr(last, base, lookup_flags); > + if (IS_ERR(dentry) && !(lookup_flags & LOOKUP_PARENT_LOCKED)) { > + inode_unlock(base->d_inode); Nit: The indentation here is wrong and the {} aren't common practice. > + } > + return dentry; > +} > + > +static struct dentry *lookup_and_lock(const struct qstr *last, > + struct dentry *base, > + unsigned int lookup_flags) > +{ > + return lookup_and_lock_nested(last, base, lookup_flags, > + I_MUTEX_PARENT); > +} > + > +void done_lookup_and_lock(struct dentry *base, struct dentry *dentry, > + unsigned int lookup_flags) Did you mean done_lookup_and_unlock()? > +{ > + d_lookup_done(dentry); > + dput(dentry); > + if (!(lookup_flags & LOOKUP_PARENT_LOCKED)) > + inode_unlock(base->d_inode); > +} > +EXPORT_SYMBOL(done_lookup_and_lock); > + > /** > * lookup_fast - do fast lockless (but racy) lookup of a dentry > * @nd: current nameidata > @@ -2754,12 +2789,9 @@ static struct dentry *__kern_path_locked(int dfd, struct filename *name, struct > path_put(path); > return ERR_PTR(-EINVAL); > } > - inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT); > - d = lookup_one_qstr(&last, path->dentry, 0); > - if (IS_ERR(d)) { > - inode_unlock(path->dentry->d_inode); > + d = lookup_and_lock(&last, path->dentry, 0); > + if (IS_ERR(d)) > path_put(path); > - } > return d; > } > > @@ -3053,6 +3085,22 @@ struct dentry *lookup_positive_unlocked(const char *name, > } > EXPORT_SYMBOL(lookup_positive_unlocked); > > +struct dentry *lookup_and_lock_one(struct mnt_idmap *idmap, > + const char *name, int len, struct dentry *base, > + unsigned int lookup_flags) > +{ > + struct qstr this; > + int err; > + > + if (!idmap) > + idmap = &nop_mnt_idmap; The callers should pass nop_mnt_idmap. That's how every function that takes this argument works. This is a lot more explicit than magically fixing this up in the function. > + err = lookup_one_common(idmap, name, base, len, &this); > + if (err) > + return ERR_PTR(err); > + return lookup_and_lock(&this, base, lookup_flags); > +} > +EXPORT_SYMBOL(lookup_and_lock_one); > + > #ifdef CONFIG_UNIX98_PTYS > int path_pts(struct path *path) > { > @@ -4071,7 +4119,6 @@ static struct dentry *filename_create(int dfd, struct filename *name, > unsigned int reval_flag = lookup_flags & LOOKUP_REVAL; > unsigned int create_flags = LOOKUP_CREATE | LOOKUP_EXCL; > int type; > - int err2; > int error; > > error = filename_parentat(dfd, name, reval_flag, path, &last, &type); > @@ -4083,36 +4130,30 @@ static struct dentry *filename_create(int dfd, struct filename *name, > * (foo/., foo/.., /////) > */ > if (unlikely(type != LAST_NORM)) > - goto out; > + goto put; > > /* don't fail immediately if it's r/o, at least try to report other errors */ > - err2 = mnt_want_write(path->mnt); > + error = mnt_want_write(path->mnt); > /* > * Do the final lookup. Suppress 'create' if there is a trailing > * '/', and a directory wasn't requested. > */ > if (last.name[last.len] && !want_dir) > create_flags &= ~LOOKUP_CREATE; > - inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT); > - dentry = lookup_one_qstr(&last, path->dentry, > - reval_flag | create_flags); > + dentry = lookup_and_lock(&last, path->dentry, reval_flag | create_flags); > if (IS_ERR(dentry)) > - goto unlock; > + goto drop; > > - if (unlikely(err2)) { > - error = err2; > + if (unlikely(error)) > goto fail; > - } > return dentry; > fail: > - d_lookup_done(dentry); > - dput(dentry); > + done_lookup_and_lock(path->dentry, dentry, reval_flag | create_flags); > dentry = ERR_PTR(error); > -unlock: > - inode_unlock(path->dentry->d_inode); > - if (!err2) > +drop: > + if (!error) > mnt_drop_write(path->mnt); > -out: > +put: > path_put(path); > return dentry; > } > @@ -4130,14 +4171,13 @@ EXPORT_SYMBOL(kern_path_create); > > void done_path_create(struct path *path, struct dentry *dentry) > { > - dput(dentry); > - inode_unlock(path->dentry->d_inode); > + done_lookup_and_lock(path->dentry, dentry, LOOKUP_CREATE); > mnt_drop_write(path->mnt); > path_put(path); > } > EXPORT_SYMBOL(done_path_create); > > -inline struct dentry *user_path_create(int dfd, const char __user *pathname, > +struct dentry *user_path_create(int dfd, const char __user *pathname, > struct path *path, unsigned int lookup_flags) > { > struct filename *filename = getname(pathname); > @@ -4510,19 +4550,18 @@ int do_rmdir(int dfd, struct filename *name) > if (error) > goto exit2; > > - inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT); > - dentry = lookup_one_qstr(&last, path.dentry, lookup_flags); > + dentry = lookup_and_lock(&last, path.dentry, lookup_flags); > error = PTR_ERR(dentry); > if (IS_ERR(dentry)) > goto exit3; > + > error = security_path_rmdir(&path, dentry); > if (error) > goto exit4; > error = vfs_rmdir(mnt_idmap(path.mnt), path.dentry->d_inode, dentry); > exit4: > - dput(dentry); > + done_lookup_and_lock(path.dentry, dentry, lookup_flags); > exit3: > - inode_unlock(path.dentry->d_inode); > mnt_drop_write(path.mnt); > exit2: > path_put(&path); > @@ -4639,11 +4678,9 @@ 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 = lookup_one_qstr(&last, path.dentry, lookup_flags); > + dentry = lookup_and_lock(&last, path.dentry, lookup_flags); > error = PTR_ERR(dentry); > if (!IS_ERR(dentry)) { > - > /* Why not before? Because we want correct error value */ > if (last.name[last.len]) > goto slashes; > @@ -4655,9 +4692,8 @@ int do_unlinkat(int dfd, struct filename *name) > error = vfs_unlink(mnt_idmap(path.mnt), path.dentry->d_inode, > dentry, &delegated_inode); > exit3: > - dput(dentry); > + done_lookup_and_lock(path.dentry, dentry, lookup_flags); > } > - inode_unlock(path.dentry->d_inode); > if (inode) > iput(inode); /* truncate the inode here */ > inode = NULL; > diff --git a/include/linux/namei.h b/include/linux/namei.h > index 0d81e571a159..76c587a5ec3a 100644 > --- a/include/linux/namei.h > +++ b/include/linux/namei.h > @@ -29,7 +29,11 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT}; > #define LOOKUP_RCU BIT(8) /* RCU pathwalk mode; semi-internal */ > #define LOOKUP_CACHED BIT(9) /* Only do cached lookup */ > #define LOOKUP_PARENT BIT(10) /* Looking up final parent in path */ > -/* 5 spare bits for pathwalk */ > +#define LOOKUP_PARENT_LOCKED BIT(11) /* filesystem sets this for nested > + * "lookup_and_lock_one" when it knows > + * parent is sufficiently locked. > + */ > +/* 4 spare bits for pathwalk */ > > /* These tell filesystem methods that we are dealing with the final component... */ > #define LOOKUP_OPEN BIT(16) /* ... in open */ > @@ -82,6 +86,15 @@ struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap, > struct dentry *lookup_one_positive_unlocked(struct mnt_idmap *idmap, > const char *name, > struct dentry *base, int len); > +struct dentry *lookup_and_lock_one(struct mnt_idmap *idmap, > + const char *name, int len, struct dentry *base, > + unsigned int lookup_flags); > +struct dentry *__lookup_and_lock_one(struct mnt_idmap *idmap, > + const char *name, int len, struct dentry *base, > + unsigned int lookup_flags); > +void done_lookup_and_lock(struct dentry *base, struct dentry *dentry, > + unsigned int lookup_flags); > +void __done_lookup_and_lock(struct dentry *dentry); > > extern int follow_down_one(struct path *); > extern int follow_down(struct path *path, unsigned int flags); > -- > 2.47.1 >