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 7D8083AE70E; Thu, 5 Feb 2026 12:38:07 +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=1770295087; cv=none; b=Gw/+IHJsseLpRf3hz83Izk7yBR+Xda2v74AEvNRZjw5yckwm8pVmY8hv/xrqkIwRhCnKXeJbNb/6ZS8Zzj/AGxlYkwsn4XzEFMnK2hWzwKmXXwAgVrn12DqsaM2a3XjoEuZWMLtgDEl+eg8vK2hyclHDEZ2HLH/ssjRWPPVzMkg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770295087; c=relaxed/simple; bh=QbRCtR0CacyYKzFJoIJunN+5tZHIJYiysqUP3sn1Aqc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Nm847cGv8l1pFxgDv1xUQDcoEOTr3CQ4i6zE2qx1tEqj2KRcbljJQYdY0zqODudVnAX+/VCeYdaKm7MLeCvXyOuXFrX4CMJ9hrFeOZQK+avdcj3PhWTmE42mVqFbsHE6apZzN2LinlM7/d3mjQrPYqA961taicyMCWLKrELhnFk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qSHNMtIn; 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="qSHNMtIn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2A69C16AAE; Thu, 5 Feb 2026 12:38:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770295087; bh=QbRCtR0CacyYKzFJoIJunN+5tZHIJYiysqUP3sn1Aqc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=qSHNMtIn2aYx7PISfiGAyJQ1vWR63E1VyXMRnILSIUleY28dg+XQ8lfpFgpLmC5lI 5JY94j5zofPxM4tDfogBiYojMv291jnvC/1OTe6kQTRGBXHBosRlUQhQ/MPMmV1XaO pbD0VlyOR4TJP2mKeJvVP7wFkUFs+ySFPCAe0dKdCGM0j35SzMe4GOrt931U+yEKP+ c4Lb6rd5NKQFR30D0YqwATn9IP/9nCvVcFInpXmBon+VwCbRVidWZm+K6dMagp9DTB rD6r/o8JQ7mpqJ836GNtcImMjLksL9+c3djR4Xmtyg4XQyabJOIlKkIeaUEnQsqJ35 l0tdvX9eXc0Gw== Message-ID: <5d273a008fc51a2fded785efbe30e5bd2a89b985.camel@kernel.org> Subject: Re: [PATCH 08/13] ovl: Simplify ovl_lookup_real_one() From: Jeff Layton To: NeilBrown , Christian Brauner , Alexander Viro , David Howells , Jan Kara , Chuck Lever , Miklos Szeredi , Amir Goldstein , John Johansen , Paul Moore , James Morris , "Serge E. Hallyn" , Stephen Smalley Cc: linux-kernel@vger.kernel.org, netfs@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-unionfs@vger.kernel.org, apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, selinux@vger.kernel.org Date: Thu, 05 Feb 2026 07:38:03 -0500 In-Reply-To: <20260204050726.177283-9-neilb@ownmail.net> References: <20260204050726.177283-1-neilb@ownmail.net> <20260204050726.177283-9-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 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-02-04 at 15:57 +1100, NeilBrown wrote: > From: NeilBrown >=20 > The primary purpose of this patch is to remove the locking from > ovl_lookup_real_one() as part of centralising all locking of directories > for name operations. >=20 > The locking here isn't needed. By performing consistency tests after > the lookup we can be sure that the result of the lookup was valid at > least for a moment, which is all the original code promised. >=20 > lookup_noperm_unlocked() is used for the lookup and it will take the > lock if needed only where it is needed. >=20 > Also: > - don't take a reference to real->d_parent. The parent is > only use for a pointer comparison, and no reference is needed for > that. > - Several "if" statements have a "goto" followed by "else" - the > else isn't needed: the following statement can directly follow > the "if" as a new statement > - Use a consistent pattern of setting "err" before performing a test > and possibly going to "fail". > - remove the "out" label (now that we don't need to dput(parent) or > unlock) and simply return from fail:. >=20 > Signed-off-by: NeilBrown > --- > fs/overlayfs/export.c | 61 ++++++++++++++++++------------------------- > 1 file changed, 26 insertions(+), 35 deletions(-) >=20 > diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c > index 83f80fdb1567..dcd28ffc4705 100644 > --- a/fs/overlayfs/export.c > +++ b/fs/overlayfs/export.c > @@ -359,59 +359,50 @@ static struct dentry *ovl_lookup_real_one(struct de= ntry *connected, > struct dentry *real, > const struct ovl_layer *layer) > { > - struct inode *dir =3D d_inode(connected); > - struct dentry *this, *parent =3D NULL; > + struct dentry *this; > struct name_snapshot name; > int err; > =20 > /* > - * Lookup child overlay dentry by real name. The dir mutex protects us > - * from racing with overlay rename. If the overlay dentry that is above > - * real has already been moved to a parent that is not under the > - * connected overlay dir, we return -ECHILD and restart the lookup of > - * connected real path from the top. > + * @connected is a directory in the overlay and @real is an object > + * on @layer which is expected to be a child of @connected. > + * The goal is to return a dentry from the overlay which corresponds > + * to @real. This is done by looking up the name from @real in > + * @connected and checking that the result meets expectations. > + * > + * Return %-ECHILD if the parent of @real no-longer corresponds to > + * @connected, and %-ESTALE if the dentry found by lookup doesn't > + * correspond to @real. > */ > - inode_lock_nested(dir, I_MUTEX_PARENT); > - err =3D -ECHILD; > - parent =3D dget_parent(real); > - if (ovl_dentry_real_at(connected, layer->idx) !=3D parent) > - goto fail; > =20 > - /* > - * We also need to take a snapshot of real dentry name to protect us > - * from racing with underlying layer rename. In this case, we don't > - * care about returning ESTALE, only from dereferencing a free name > - * pointer because we hold no lock on the real dentry. > - */ > take_dentry_name_snapshot(&name, real); > - /* > - * No idmap handling here: it's an internal lookup. > - */ > - this =3D lookup_noperm(&name.name, connected); > + this =3D lookup_noperm_unlocked(&name.name, connected); > release_dentry_name_snapshot(&name); > + > + err =3D -ECHILD; > + if (ovl_dentry_real_at(connected, layer->idx) !=3D real->d_parent) > + goto fail; > + > err =3D PTR_ERR(this); > - if (IS_ERR(this)) { > + if (IS_ERR(this)) > goto fail; > - } else if (!this || !this->d_inode) { > - dput(this); > - err =3D -ENOENT; > + > + err =3D -ENOENT; > + if (!this || !this->d_inode) > goto fail; > - } else if (ovl_dentry_real_at(this, layer->idx) !=3D real) { > - dput(this); > - err =3D -ESTALE; > + > + err =3D -ESTALE; > + if (ovl_dentry_real_at(this, layer->idx) !=3D real) > goto fail; > - } > =20 > -out: > - dput(parent); > - inode_unlock(dir); > return this; > =20 > fail: > pr_warn_ratelimited("failed to lookup one by real (%pd2, layer=3D%d, co= nnected=3D%pd2, err=3D%i)\n", > real, layer->idx, connected, err); > - this =3D ERR_PTR(err); > - goto out; > + if (!IS_ERR(this)) > + dput(this); > + return ERR_PTR(err); > } > =20 > static struct dentry *ovl_lookup_real(struct super_block *sb, Reviewed-by: Jeff Layton