linux-kernel - Re: [PATCH v6 3/7] kernfs: use VFS negative dentry caching

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <2ee74cbed729d66a38a5c7de9c4608d02fb89f26.camel@themaw.net>
Date:   Sat, 12 Jun 2021 08:43:13 +0800
From:   Ian Kent <raven@...maw.net>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, Eric Sandeen <sandeen@...deen.net>,
        Fox Chen <foxhlchen@...il.com>,
        Brice Goglin <brice.goglin@...il.com>,
        Rick Lindsley <ricklind@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 3/7] kernfs: use VFS negative dentry caching

On Sat, 2021-06-12 at 00:07 +0000, Al Viro wrote:
> On Wed, Jun 09, 2021 at 04:50:27PM +0800, Ian Kent wrote:
> 
> > +       if (d_really_is_negative(dentry)) {
> > +               struct dentry *d_parent = dget_parent(dentry);
> > +               struct kernfs_node *parent;
> 
> What the hell is dget_parent() for?  You don't do anything blocking
> here, so why not simply grab dentry->d_lock - that'll stabilize
> the value of ->d_parent just fine.  Just don't forget to drop the
> lock before returning and that's it...

Thanks Al, I'll change it.

> 
> > +               /* If the kernfs parent node has changed discard
> > and
> > +                * proceed to ->lookup.
> > +                */
> > +               parent = kernfs_dentry_node(d_parent);
> > +               if (parent) {
> > +                       if (kernfs_dir_changed(parent, dentry)) {
> > +                               dput(d_parent);
> > +                               return 0;
> > +                       }
> > +               }
> > +               dput(d_parent);
> > +
> > +               /* The kernfs node doesn't exist, leave the dentry
> > +                * negative and return success.
> > +                */
> > +               return 1;
> > +       }