Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220622085146.444516-1-sunliming@kylinos.cn> <YrLwU27DNm0YWOvB@ZenIV>
In-Reply-To: <YrLwU27DNm0YWOvB@ZenIV>
From:   sunliming <kelulanainsley@gmail.com>
Date:   Thu, 23 Jun 2022 11:44:29 +0800
Message-ID: <CAJncD7RuTTLoRS_pzvn729_SX5Xsv6Pub44eCD_RbbANjn9joA@mail.gmail.com>
Subject: Re: [PATCH] walk_component(): get inode in lookup_slow branch
 statement block
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        sunliming@kylino.cn
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Al Viro <viro@zeniv.linux.org.uk> =E4=BA=8E2022=E5=B9=B46=E6=9C=8822=E6=97=
=A5=E5=91=A8=E4=B8=89 18:35=E5=86=99=E9=81=93=EF=BC=9A
>
> On Wed, Jun 22, 2022 at 04:51:46PM +0800, sunliming wrote:
> > The inode variable is used as a parameter by the step_into function,
> > but is not assigned a value in the sub-lookup_slow branch path. So
> > get the inode in the sub-lookup_slow branch path.
>
> Take a good look at handle_mounts() and the things it does when
> *not* in RCU mode (i.e. LOOKUP_RCU is not set).  Specifically,
>                 *inode =3D d_backing_inode(path->dentry);
>                 *seqp =3D 0; /* out of RCU mode, so the value doesn't mat=
ter */
> this part.
>
> IOW, the values passed to step_into() in inode/seq are overridden unless
> we stay in RCU mode.  And if we'd been through lookup_slow(), we'd been
> out of RCU mode since before we called step_into().

It might be more appropriate and easier to understand to do this
before parameter passing in the top-level  walk_component function=EF=BC=9F