Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 20 Dec 2019 11:50:25 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Amir Goldstein <amir73il@gmail.com>
Cc:     Chris Down <chris@chrisdown.name>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jeff Layton <jlayton@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tejun Heo <tj@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>, kernel-team@fb.com,
        Hugh Dickins <hughd@google.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        "zhengbin (A)" <zhengbin13@huawei.com>
Subject: Re: [PATCH] fs: inode: Reduce volatile inode wraparound risk when
 ino_t is 64 bit
Message-ID: <20191220195025.GA9469@bombadil.infradead.org>
References: <20191220024936.GA380394@chrisdown.name>
 <CAOQ4uxjqSWcrA1reiyit9DRt+aq2tXBxLdPE31RrYw1yr=4hjg@mail.gmail.com>
 <20191220121615.GB388018@chrisdown.name>
 <CAOQ4uxgo_kAttnB4N1+om5gScYSDn3FXAr+_GUiqNy_79iiLXQ@mail.gmail.com>
 <20191220164632.GA26902@bombadil.infradead.org>
 <CAOQ4uxhYY9Ep1ncpU+E3bWg4ZpR8pjvLJMA5vj+7frEJ2KTwsg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAOQ4uxhYY9Ep1ncpU+E3bWg4ZpR8pjvLJMA5vj+7frEJ2KTwsg@mail.gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Dec 20, 2019 at 07:35:38PM +0200, Amir Goldstein wrote:
> On Fri, Dec 20, 2019 at 6:46 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Fri, Dec 20, 2019 at 03:41:11PM +0200, Amir Goldstein wrote:
> > > Suggestion:
> > > 1. Extend the kmem_cache API to let the ctor() know if it is
> > > initializing an object
> > >     for the first time (new page) or recycling an object.
> >
> > Uh, what?  The ctor is _only_ called when new pages are allocated.
> > Part of the contract with the slab user is that objects are returned to
> > the slab in an initialised state.
> 
> Right. I mixed up the ctor() with alloc_inode().
> So is there anything stopping us from reusing an existing non-zero
> value of  i_ino in shmem_get_inode()? for recycling shmem ino
> numbers?

I think that would be an excellent solution to the problem!  At least,
I can't think of any problems with it.