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Date:   Sun, 3 Oct 2021 18:07:20 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Rustam Kovhaev <rkovhaev@gmail.com>
cc:     Vlastimil Babka <vbabka@suse.cz>,
        Dave Chinner <david@fromorbit.com>, djwong@kernel.org,
        linux-xfs@vger.kernel.org, cl@linux.com, penberg@kernel.org,
        iamjoonsoo.kim@lge.com, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        gregkh@linuxfoundation.org, Al Viro <viro@zeniv.linux.org.uk>,
        dvyukov@google.com
Subject: Re: [PATCH] xfs: use kmem_cache_free() for kmem_cache objects
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References: <20210929212347.1139666-1-rkovhaev@gmail.com> <20210930044202.GP2361455@dread.disaster.area> <17f537b3-e2eb-5d0a-1465-20f3d3c960e2@suse.cz> <YVYGcLbu/aDKXkag@nuc10> <a9b3cd91-8ee6-a654-b2a8-00c3efb69559@suse.cz> <YVZXF3mbaW+Pe+Ji@nuc10>
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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..)