Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <162322846765.361452.17051755721944717990.stgit@web.messagingengine.com>
 <162322872534.361452.17619177755627322271.stgit@web.messagingengine.com>
In-Reply-To: <162322872534.361452.17619177755627322271.stgit@web.messagingengine.com>
From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Fri, 11 Jun 2021 15:13:37 +0200
Message-ID: <CAJfpegtQd-eYqdSee7CwOFz=uViDV4=P+BmKR_Ciryz1wEe0FQ@mail.gmail.com>
Subject: Re: [PATCH v6 6/7] kernfs: add kernfs_need_inode_refresh()
To:     Ian Kent <raven@themaw.net>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>, Eric Sandeen <sandeen@sandeen.net>,
        Fox Chen <foxhlchen@gmail.com>,
        Brice Goglin <brice.goglin@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Rick Lindsley <ricklind@linux.vnet.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Carlos Maiolino <cmaiolino@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, 9 Jun 2021 at 10:52, Ian Kent <raven@themaw.net> wrote:
>
> Now the kernfs_rwsem read lock is held for kernfs_refresh_inode() and
> the i_lock taken to protect inode updates there can be some contention
> introduced when .permission() is called with concurrent path walks in
> progress.
>
> Since .permission() is called frequently during path walks it's worth
> checking if the update is actually needed before taking the lock and
> performing the update.
>
> Signed-off-by: Ian Kent <raven@themaw.net>

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>