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From:   David Howells <dhowells@redhat.com>
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References: <20200117144055.GB3215@pi3> <CAJKOXPeCVwZfBsCVbc9RQUGi0UfWQw0uFamPiQasiO8fSthFsQ@mail.gmail.com> <433863.1579270803@warthog.procyon.org.uk>
To:     Krzysztof Kozlowski <krzk@kernel.org>
Cc:     dhowells@redhat.com,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        linux-nfs@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Scott Mayhew <smayhew@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>
Subject: Re: [BISECT BUG] NFS v4 root not working after 6d972518b821 ("NFS: Add fs_context support.")
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Date:   Fri, 17 Jan 2020 15:12:38 +0000
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Krzysztof Kozlowski <krzk@kernel.org> wrote:

> mount.nfs4 -o vers=4,nolock 192.168.1.10:/srv/nfs/odroidhc1 /new_root

Okay, it looks like the mount command makes two attempts at mounting.
Firstly, it does this:

> [   22.938314] NFSOP 'source=192.168.1.10:/srv/nfs/odroidhc1'
> [   22.942638] NFSOP 'nolock=(null)'
> [   22.945772] NFSOP 'vers=4.2'
> [   22.948660] NFSOP 'addr=192.168.1.10'
> [   22.952350] NFSOP 'clientaddr=192.168.1.12'
> [   22.956831] NFS4: Couldn't follow remote path

Which accepts the "vers=4.2" parameter as there's no check that that is
actually valid given the configuration, but then fails later.  Secondly, it
does this:

> [   22.971001] NFSOP 'source=192.168.1.10:/srv/nfs/odroidhc1'
> [   22.975217] NFSOP 'nolock=(null)'
> [   22.978444] NFSOP 'vers=4'
> [   22.981265] NFSOP 'minorversion=1'
> [   22.984513] NFS: Value for 'minorversion' out of range
> mount.nfs4: Numerical result out of range

which fails because of the minorversion=1 specification, where the kernel
config didn't enable NFS_V4_1.

It looks like it ought to have failed prior to these patches in the same way:

		case Opt_minorversion:
			if (nfs_get_option_ul(args, &option))
				goto out_invalid_value;
			if (option > NFS4_MAX_MINOR_VERSION)
				goto out_invalid_value;
			mnt->minorversion = option;
			break;

David