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From:   "NeilBrown" <neilb@suse.de>
To:     "Daire Byrne" <daire@dneg.com>
Cc:     "Trond Myklebust" <trond.myklebust@hammerspace.com>,
        "Anna Schumaker" <Anna.Schumaker@netapp.com>,
        "linux-nfs" <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH/rfc v2] NFS: introduce NFS namespaces.
In-reply-to: <CAPt2mGPSeK6YHPQ8r6Z0UJv4mJnRAcEEc4VmLaENo91-K8P=fQ@mail.gmail.com>
References: <162458475606.28671.1835069742861755259@noble.neil.brown.name>,
 <162510089174.7211.449831430943803791@noble.neil.brown.name>,
 <CAPt2mGMgCHwvmy2MA4c2E316xVYPiRy4pRdcX4-1EAALfcxz+A@mail.gmail.com>,
 <162513954601.3001.5763461156445846045@noble.neil.brown.name>,
 <CAPt2mGNCV7Sh0uXA0ihpuSVcecXW=5cMUAfiS0tYr_cTQ0Du8w@mail.gmail.com>,
 <162535340922.16506.4184249866230493262@noble.neil.brown.name>,
 <CAPt2mGNOMh0uWozi=L5H6X7aKUuh_+-QxJ7OK9e6ELiKnSh1hg@mail.gmail.com>,
 <162562036711.12832.7541413783945987660@noble.neil.brown.name>,
 <CAPt2mGM6mcqM9orzHuyTVgX2pnG5Y7nLeM85tdZ5LoDO9XozBA@mail.gmail.com>,
 <162569314954.31036.11087071768390664533@noble.neil.brown.name>,
 <CAPt2mGPSeK6YHPQ8r6Z0UJv4mJnRAcEEc4VmLaENo91-K8P=fQ@mail.gmail.com>
Date:   Thu, 08 Jul 2021 09:18:55 +1000
Message-id: <162569993532.31036.942509527308749032@noble.neil.brown.name>
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On Thu, 08 Jul 2021, Daire Byrne wrote:
> On Wed, 7 Jul 2021 at 22:25, NeilBrown <neilb@suse.de> wrote:
> >
> > That's pretty solid evidence!
> >
> > I just realized that the stack trace you reported mentions
> > "kfree_const()".
> > My latest patch doesn't include that, and nfs doesn't use it at all.
> > Might you still be using the older patch?
> >
> > NeilBrown
>=20
> Oh... the last stack trace, the readdir one? I don't see kfree_const
> myself but I may have a case of word blindness. The first one I
> reported definitely has kfree_const but after your latest patch, this
> last one around readdir doesn't seem to?
>=20
> I'm pretty sure I have your latest patch (with kfree instead of
> kfree_const) correctly applied. Though, I will double check that the
> correct kernel and modules were then installed properly on my test VM.

sorry - my bad..

I think I've found it.  Rather than sending the whole patch, here is the
incremental fix.  But not clearing this pointer, I risk the value in it
being freed twice.  That might lead to what you saw.

Thanks,
NeilBrown


diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index 7c644a31d304..9e34af223ce6 100644
--- a/fs/nfs/fs_context.c
+++ b/fs/nfs/fs_context.c
@@ -1451,6 +1451,7 @@ static int nfs_fs_context_dup(struct fs_context *fc, st=
ruct fs_context *src_fc)
 	ctx->nfs_server.export_path	=3D NULL;
 	ctx->nfs_server.hostname	=3D NULL;
 	ctx->fscache_uniq		=3D NULL;
+	ctx->namespace			=3D NULL;
 	ctx->clone_data.fattr		=3D NULL;
 	fc->fs_private =3D ctx;
 	return 0;