Re: WARNING bisected (was Re: [PATCH v7 08/10] mm: rework non-root kmem_cache lifecycle management)

[Roman Gushchin]

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:
> > > 
> > > 
> > > Yes, rmmod has to be called directly after the guest shutdown to
> > > see the issue.
> > > See my 2nd mail.
> > 
> > I see. Do you know, which kmem_cache it is? If not, can you, please,
> > figure it out?
> > 
> > I tried to reproduce the issue, but wasn't successful so far. So I
> > wonder
> > what can make your case special.
> 
> I do not know either, but have a guess.
> 
> 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.
> 

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!