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Mon, 28 Sep 2026 23:43:32 -0400 (EDT) From: NeilBrown To: Miklos Szeredi , Amir Goldstein , Kees Cook , Joel Granados , Richard Weinberger , Anton Ivanov , Johannes Berg , Breno Leitao , Andreas Hindborg , Jan Harkes , Hugh Dickins , Baolin Wang , Namjae Jeon , Hyunchul Lee , Carlos Maiolino , Alexander Viro , Christian Brauner Cc: Jeff Layton , Jan Kara , linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev, linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org, linux-um@lists.infradead.org, codalist@coda.cs.cmu.edu, coda@cs.cmu.edu, linux-mm@kvack.org, ntfs@lists.linux.dev, linux-xfs@vger.kernel.org Subject: [PATCH 7/7] ovl: stop using lookup_one() in ovl_iterate(). Date: Tue, 29 Sep 2026 13:36:07 +1000 Message-ID: <20260929034158.1455429-8-neilb@ownmail.net> X-Mailer: git-send-email 2.50.0.107.gf914562f5916.dirty In-Reply-To: <20260929034158.1455429-1-neilb@ownmail.net> References: <20260929034158.1455429-1-neilb@ownmail.net> Reply-To: NeilBrown Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: NeilBrown lookup_one() is expected to be removed as it does not fit well with proposed changes to directory locking. Specifically d_alloc_parallel() will be ordered outside of i_rwsem and as iterate_shared() is called with i_rwsem held it is not safe to call d_alloc_parallel(). We can instead call d_alloc_trylock() and then call the ->lookup, but that can fail if there is a lookup attempt concurrent with the readdir(). ovl cannot afford for the lookup to fail as that could produce incorrect results, and it cannot safely drop i_rwsem temporarily as that could introduce races with handling of the directory cache. Instead we rely on the fact that ovl_iterate() has an exclusive lock on the directory, so any concurrent lookup will wait for the ovl_iterate() call to complete. We allocate a separate dentry and if the lookup is successful, it is hashed with the result. When the concurrent lookup gets i_rwsem it mustn't do its own lookup - it must use the existing dentry. This is found, if it exists, using try_lookup_noperm(). Signed-off-by: NeilBrown --- fs/overlayfs/namei.c | 12 ++++++++++++ fs/overlayfs/readdir.c | 26 ++++++++++++++++++++++++-- 2 files changed, 36 insertions(+), 2 deletions(-) diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c index ca899fdfaafd..f56e33fd4d6b 100644 --- a/fs/overlayfs/namei.c +++ b/fs/overlayfs/namei.c @@ -1385,6 +1385,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry, struct ovl_fs *ofs = OVL_FS(dentry->d_sb); struct ovl_entry *poe = OVL_E(dentry->d_parent); bool check_redirect = (ovl_redirect_follow(ofs) || ofs->numdatalayer); + struct dentry *alias; int err; struct ovl_lookup_ctx ctx = { .dentry = dentry, @@ -1399,6 +1400,17 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry, if (dentry->d_name.len > ofs->namelen) return ERR_PTR(-ENAMETOOLONG); + /* + * The existence of this in-lookup dentry might have forced + * readdir to do the lookup with a new dentry. If so we must + * return that one. + */ + alias = try_lookup_noperm(&QSTR_LEN(dentry->d_name.name, + dentry->d_name.len), + dentry->d_parent); + if (alias && !IS_ERR(alias)) + return alias; + with_ovl_creds(dentry->d_sb) err = ovl_lookup_layers(&ctx, &d); diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index e7fe29cb6028..bc41da4bace8 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -574,8 +574,30 @@ static int ovl_cache_update(const struct path *path, struct ovl_cache_entry *p, } } /* This checks also for xwhiteouts */ - this = lookup_one(mnt_idmap(path->mnt), &QSTR_LEN(p->name, p->len), dir); - if (IS_ERR_OR_NULL(this) || !this->d_inode) { + this = d_alloc_trylock(dir, &QSTR_LEN(p->name, p->len)); + if (this == ERR_PTR(-EWOULDBLOCK)) { + /* + * Some other thread is looking up this name and will + * block on i_rwsem before it can complete the lookup. + * We will do the lookup in a new dentry and when that + * lookup gets a turn it will find and return this + * dentry. + */ + this = d_alloc_name(dir, p->name); + if (!this) + this = ERR_PTR(-ENOMEM); + } + if (!IS_ERR(this) && d_unhashed(this)) { + /* Either we got an in-lookup or we made our own unhashed */ + struct dentry *alias = ovl_lookup(dir->d_inode, this, 0); + + d_lookup_done(this); + if (alias) { + dput(this); + this = alias; + } + } + if (IS_ERR(this) || !this->d_inode) { /* Mark a stale entry */ p->is_whiteout = true; if (IS_ERR(this)) { -- 2.50.0.107.gf914562f5916.dirty