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From:   Anna Schumaker <schumakeranna@gmail.com>
Date:   Thu, 12 Nov 2020 09:07:17 -0500
Message-ID: <CAFX2JfmNHLyTL+y5yG58AkSEmsXcmP65bk1KLT6NuOsgXd=4Qw@mail.gmail.com>
Subject: Re: [PATCH] NFSv4.2: fix failure to unregister shrinker
To:     "J. Bruce Fields" <bfields@fieldses.org>
Cc:     Trond Myklebust <trondmy@hammerspace.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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No need to resend! I'll make sure the fixes & cc line get added to the commit

On Thu, Nov 12, 2020 at 9:03 AM J. Bruce Fields <bfields@fieldses.org> wrote:
>
> Looks like this patch got lost, do you need me to resend?
>
> I should also have added a stable cc and a
>
>         Fixes: 95ad37f90c33 "NFSv4.2: add client side xattr caching."
>
> --b.
>
> On Wed, Oct 21, 2020 at 10:34:15AM -0400, bfields wrote:
> > From: "J. Bruce Fields" <bfields@redhat.com>
> >
> > We forgot to unregister the nfs4_xattr_large_entry_shrinker.
> >
> > That leaves the global list of shrinkers corrupted after unload of the
> > nfs module, after which possibly unrelated code that calls
> > register_shrinker() or unregister_shrinker() gets a BUG() with
> > "supervisor write access in kernel mode".
> >
> > And similarly for the nfs4_xattr_large_entry_lru.
> >
> > Reported-by: Kris Karas <bugs-a17@moonlit-rail.com>
> > Tested-By: Kris Karas <bugs-a17@moonlit-rail.com>
> > Signed-off-by: J. Bruce Fields <bfields@redhat.com>
> > ---
> >  fs/nfs/nfs42xattr.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/fs/nfs/nfs42xattr.c b/fs/nfs/nfs42xattr.c
> > index 86777996cfec..55b44a42d625 100644
> > --- a/fs/nfs/nfs42xattr.c
> > +++ b/fs/nfs/nfs42xattr.c
> > @@ -1048,8 +1048,10 @@ int __init nfs4_xattr_cache_init(void)
> >
> >  void nfs4_xattr_cache_exit(void)
> >  {
> > +     unregister_shrinker(&nfs4_xattr_large_entry_shrinker);
> >       unregister_shrinker(&nfs4_xattr_entry_shrinker);
> >       unregister_shrinker(&nfs4_xattr_cache_shrinker);
> > +     list_lru_destroy(&nfs4_xattr_large_entry_lru);
> >       list_lru_destroy(&nfs4_xattr_entry_lru);
> >       list_lru_destroy(&nfs4_xattr_cache_lru);
> >       kmem_cache_destroy(nfs4_xattr_cache_cachep);
> > --
> > 2.26.2
> >