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 CFF4017BBF; Fri, 7 Feb 2025 00:23:40 +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=1738887820; cv=none; b=gC7mq5RaHfMPQkugxt2CKuwLJxsaYhbrchzHg9e6LpMVqkVegAOyIuG0RHCjO2ObTR0gG4eu+8m/JgA+L5FTS/hexd2quTyG7oHZrewITOVjZvR1XUornvkaHvUWs9ekTkeiiYgTIAF8/o/3G0TiKH9+HARXnJyt0PsMWVI6EuU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738887820; c=relaxed/simple; bh=WsDlcnI4bhIi7Crlb2pW1EAhVlKyqIiH9J9KBTUr7LE=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=UAnd28Hctr7uwSl7E+lvSI4MIyXWn9F/e7iTuPLvTLOZqn1R41v1b6JqPo0Y6TJ02jQOpysddODymMYF2ySZTgK2PnV5n2M2d6YtZASE3vRpek6Clo9q10NWNQ5bLtx4EOvB5aEKVHb6nwBUEgs3WnsU55kD2RKovHPZGJQ9Kv0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FxyYXnNG; 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="FxyYXnNG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BA428C4CEDF; Fri, 7 Feb 2025 00:23:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738887820; bh=WsDlcnI4bhIi7Crlb2pW1EAhVlKyqIiH9J9KBTUr7LE=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=FxyYXnNGgBq85SSrmx3iNwV7UkZ67o29TDME13PfdiSvQnBea0WIc4T2yxxD+4iaY ZnllMXF1x/XiQblOIA5cFGCFjD5fg+p21TTA+BbL3/wv3KHJ/6CdouCQXWMhCdtJjE C5cw756Ykk62jIlzgFRn3FzceIJVHNNLHM9MPQVxEwglgMchQAW33MzOZsc3i9kjVE 8ZJsUItaS0ukmtco5yErCQBgG8zGZpo8itLQboJjUOWzhkJTU9c/3LjLM43IQ3qSaO sTlOOr3QhYEdZ0HtiR7Qg2Tq6e59c88Br3ilyfcOBKBuBUw4k4+pb8HOol13hV+6Sl ks7tIqym+eatg== Message-ID: <6f63593946ef08dc9535b2d7c51d17c884b7aafe.camel@kernel.org> Subject: Re: [PATCH 03/19] VFS: use d_alloc_parallel() in lookup_one_qstr_excl() and rename it. From: Jeff Layton To: NeilBrown Cc: Alexander Viro , Christian Brauner , Jan Kara , Linus Torvalds , Dave Chinner , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 06 Feb 2025 19:23:38 -0500 In-Reply-To: <173888666051.22054.2064348642111556769@noble.neil.brown.name> References: <>, <017ca787f3a167302281b65e60d301d9f1c0f5de.camel@kernel.org> <173888666051.22054.2064348642111556769@noble.neil.brown.name> 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 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2025-02-07 at 11:04 +1100, NeilBrown wrote: > On Fri, 07 Feb 2025, Jeff Layton wrote: > > On Thu, 2025-02-06 at 16:42 +1100, NeilBrown wrote: > > > lookup_one_qstr_excl() is used for lookups prior to directory > > > modifications, whether create, unlink, rename, or whatever. > > >=20 > > > To prepare for allowing modification to happen in parallel, change > > > lookup_one_qstr_excl() to use d_alloc_parallel(). > > >=20 > > > To reflect this, name is changed to lookup_one_qtr() - as the directo= ry > > > may be locked shared. > > >=20 > > > If any for the "intent" LOOKUP flags are passed, the caller must ensu= re > > > d_lookup_done() is called at an appropriate time. If none are passed > > > then we can be sure ->lookup() will do a real lookup and d_lookup_don= e() > > > is called internally. > > >=20 > > > Signed-off-by: NeilBrown > > > --- > > > fs/namei.c | 47 +++++++++++++++++++++++++----------------= -- > > > fs/smb/server/vfs.c | 7 ++++--- > > > include/linux/namei.h | 9 ++++++--- > > > 3 files changed, 37 insertions(+), 26 deletions(-) > > >=20 > > > diff --git a/fs/namei.c b/fs/namei.c > > > index 5cdbd2eb4056..d684102d873d 100644 > > > --- a/fs/namei.c > > > +++ b/fs/namei.c > > > @@ -1665,15 +1665,13 @@ static struct dentry *lookup_dcache(const str= uct qstr *name, > > > } > > > =20 > > > /* > > > - * Parent directory has inode locked exclusive. This is one > > > - * and only case when ->lookup() gets called on non in-lookup > > > - * dentries - as the matter of fact, this only gets called > > > - * when directory is guaranteed to have no in-lookup children > > > - * at all. > > > + * Parent directory has inode locked: exclusive or shared. > > > + * If @flags contains any LOOKUP_INTENT_FLAGS then d_lookup_done() > > > + * must be called after the intended operation is performed - or abo= rted. > > > */ > > > -struct dentry *lookup_one_qstr_excl(const struct qstr *name, > > > - struct dentry *base, > > > - unsigned int flags) > > > +struct dentry *lookup_one_qstr(const struct qstr *name, > > > + struct dentry *base, > > > + unsigned int flags) > > > { > > > struct dentry *dentry =3D lookup_dcache(name, base, flags); > > > struct dentry *old; > > > @@ -1686,18 +1684,25 @@ struct dentry *lookup_one_qstr_excl(const str= uct qstr *name, > > > if (unlikely(IS_DEADDIR(dir))) > > > return ERR_PTR(-ENOENT); > > > =20 > > > - dentry =3D d_alloc(base, name); > > > - if (unlikely(!dentry)) > > > + dentry =3D d_alloc_parallel(base, name); > > > + if (unlikely(IS_ERR_OR_NULL(dentry))) > > > return ERR_PTR(-ENOMEM); > > > + if (!d_in_lookup(dentry)) > > > + /* Raced with another thread which did the lookup */ > > > + return dentry; > > > =20 > > > old =3D dir->i_op->lookup(dir, dentry, flags); > > > if (unlikely(old)) { > > > + d_lookup_done(dentry); > > > dput(dentry); > > > dentry =3D old; > > > } > > > + if ((flags & LOOKUP_INTENT_FLAGS) =3D=3D 0) > > > + /* ->lookup must have given final answer */ > > > + d_lookup_done(dentry); > >=20 > > This is kind of an ugly thing for the callers to get right. I think it > > would be cleaner to just push the d_lookup_done() into all of the > > callers that don't pass any intent flags, and do away with this. >=20 > I don't understand your concern. This does not impose on callers, > rather it relieves them of a burden. d_lookup_done() is fully > idempotent so if a caller does call it, there is no harm done. >=20 > In the final result of my series there are 4 callers of this function. > 1/ lookup_and_lock() which must always be balanced with > done_lookup_and_lock(), which calls d_lookup_done() > 2/ lookup_and_lock_rename() which is similarly balance with > done_lookup_and_lock_rename().=20 > 3/ ksmbd_vfs_path_lookup_locked() which passes zero for the flags and so > doesn't need d_lookup_done() > 4/ ksmbd_vfs_rename() which calls d_lookup_done() as required. >=20 > So if I dropped this code it would only affect one caller which would > need to add a call to d_lookup_done() probably immediately after the > successful return of lookup_one_qstr(). > While that wouldn't hurt much, I don't see that it would help much > either. >=20 My concern is about the complex return handling. If the flags are 0, then I don't need to call d_lookup_done(), but if they aren't 0, then I do. That's just an easy opportunity to get it wrong if new callers are added. My preference would be that the caller must always call d_lookup_done() on a successful return. If ksmbd_vfs_path_lookup_locked() has to call it immediately afterward, then that's fine. No need for this special handling in a generic function, just for a single caller. --=20 Jeff Layton