linux-kernel - Re: [PATCH] xfs: use kmem_cache_free() for kmem

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Message-ID: <20211012204320.GP24307@magnolia>
Date:   Tue, 12 Oct 2021 13:43:20 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Rustam Kovhaev <rkovhaev@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dave Chinner <david@...morbit.com>, linux-xfs@...r.kernel.org,
        cl@...ux.com, penberg@...nel.org, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, gregkh@...uxfoundation.org,
        Al Viro <viro@...iv.linux.org.uk>, dvyukov@...gle.com
Subject: Re: [PATCH] xfs: use kmem_cache_free() for kmem_cache objects

On Sun, Oct 03, 2021 at 06:07:20PM -0700, David Rientjes wrote:
> On Thu, 30 Sep 2021, Rustam Kovhaev wrote:
> 
> > > >> I think it's fair if something like XFS (not meant for tiny systems AFAIK?)
> > > >> excludes SLOB (meant for tiny systems). Clearly nobody tried to use these
> > > >> two together last 5 years anyway.
> > > > 
> > > > +1 for adding Kconfig option, it seems like some things are not meant to
> > > > be together.
> > > 
> > > But if we patch SLOB, we won't need it.
> > 
> > OK, so we consider XFS on SLOB a supported configuration that might be
> > used and should be tested.
> > I'll look into maybe adding a config with CONFIG_SLOB and CONFIG_XFS_FS
> > to syzbot.
> > 
> > It seems that we need to patch SLOB anyway, because any other code can
> > hit the very same issue.
> > 
> 
> It's probably best to introduce both (SLOB fix and Kconfig change for 
> XFS), at least in the interim because the combo of XFS and SLOB could be 
> broken in other ways.  If syzbot doesn't complain with a patched kernel to 
> allow SLOB to be used with XFS, then we could potentially allow them to be 
> used together.
> 
> (I'm not sure that this freeing issue is the *only* thing that is broken, 
> nor that we have sufficient information to make that determination right 
> now..)

I audited the entire xfs (kernel) codebase and didn't find any other
usage errors.  Thanks for the patch; I'll apply it to for-next.

--D