linux-kernel - Re: [PATCH] fs: inode: Reduce volatile inode wraparound risk when ino

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Date:   Fri, 20 Dec 2019 11:50:25 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Chris Down <chris@...isdown.name>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>, kernel-team@...com,
        Hugh Dickins <hughd@...gle.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        "zhengbin (A)" <zhengbin13@...wei.com>
Subject: Re: [PATCH] fs: inode: Reduce volatile inode wraparound risk when
 ino_t is 64 bit

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@...radead.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.