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From:   Roman Gushchin <guro@fb.com>
To:     Rik van Riel <riel@fb.com>
CC:     Christian Borntraeger <borntraeger@de.ibm.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
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        Janosch Frank <frankja@linux.ibm.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: WARNING bisected (was Re: [PATCH v7 08/10] mm: rework non-root
 kmem_cache lifecycle management)
Thread-Topic: WARNING bisected (was Re: [PATCH v7 08/10] mm: rework non-root
 kmem_cache lifecycle management)
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Date:   Thu, 21 Nov 2019 20:55:27 +0000
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On Thu, Nov 21, 2019 at 12:43:01PM -0800, Rik van Riel wrote:
> On Thu, 2019-11-21 at 13:45 -0500, Roman Gushchin wrote:
> > On Thu, Nov 21, 2019 at 05:59:54PM +0100, Christian Borntraeger
> > wrote:
> > >=20
> > >=20
> > > Yes, rmmod has to be called directly after the guest shutdown to
> > > see the issue.
> > > See my 2nd mail.
> >=20
> > I see. Do you know, which kmem_cache it is? If not, can you, please,
> > figure it out?
> >=20
> > I tried to reproduce the issue, but wasn't successful so far. So I
> > wonder
> > what can make your case special.
>=20
> I do not know either, but have a guess.
>=20
> My guess would be that either the slab object or the
> slab page is RCU freed, and the kmem_cache destruction
> is called before that RCU callback has completed.
>=20

I've a reproducer, but it requires SLAB_TYPESAFE_BY_RCU to panic.
The only question is if it's the same or different issues.
As soon as I'll have a fix, I'll post it here to test.

Thanks!