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Message-ID: <40e1bf417c635ce303f9e42ddb0e3dbd90022477.camel@kernel.org>
Subject: Re: [PATCH 1/9] nfsd: hold ->cl_lock for hash_delegation_locked()
From:   Jeff Layton <jlayton@kernel.org>
To:     NeilBrown <neilb@suse.de>, Chuck Lever <chuck.lever@oracle.com>
Cc:     linux-nfs@vger.kernel.org, Olga Kornievskaia <kolga@netapp.com>,
        Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey <tom@talpey.com>
Date:   Fri, 17 Nov 2023 05:59:13 -0500
In-Reply-To: <20231117022121.23310-2-neilb@suse.de>
References: <20231117022121.23310-1-neilb@suse.de>
         <20231117022121.23310-2-neilb@suse.de>
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On Fri, 2023-11-17 at 13:18 +1100, NeilBrown wrote:
> The protocol for creating a new state in nfsd is to allocated the state
> leaving it largely uninitialised, add that state to the ->cl_stateids
> idr so as to reserve a state id, then complete initialisation of the
> state and only set ->sc_type to non-zero once the state is fully
> initialised.
>=20
> If a state is found in the idr with ->sc_type =3D=3D 0, it is ignored.
> The ->cl_lock list is used to avoid races - it is held while checking
> sc_type during lookup, and held when a non-zero value is stored in
> ->sc_type.
>=20
> ... except... hash_delegation_locked() finalises the initialisation of a
> delegation state, but does NOT hold ->cl_lock.
>=20
> So this patch takes ->cl_lock at the appropriate time w.r.t other locks,
> and so ensures there are no races (which are extremely unlikely in any
> case).
>=20
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
>  fs/nfsd/nfs4state.c | 3 +++
>  1 file changed, 3 insertions(+)
>=20
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 65fd5510323a..6368788a7d4e 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1317,6 +1317,7 @@ hash_delegation_locked(struct nfs4_delegation *dp, =
struct nfs4_file *fp)
> =20
>  	lockdep_assert_held(&state_lock);
>  	lockdep_assert_held(&fp->fi_lock);
> +	lockdep_assert_held(&clp->cl_lock);
> =20
>  	if (nfs4_delegation_exists(clp, fp))
>  		return -EAGAIN;
> @@ -5609,12 +5610,14 @@ nfs4_set_delegation(struct nfsd4_open *open, stru=
ct nfs4_ol_stateid *stp,
>  		goto out_unlock;
> =20
>  	spin_lock(&state_lock);
> +	spin_lock(&clp->cl_lock);
>  	spin_lock(&fp->fi_lock);
>  	if (fp->fi_had_conflict)
>  		status =3D -EAGAIN;
>  	else
>  		status =3D hash_delegation_locked(dp, fp);
>  	spin_unlock(&fp->fi_lock);
> +	spin_unlock(&clp->cl_lock);
>  	spin_unlock(&state_lock);
> =20
>  	if (status)

I know it's (supposedly) an unlikely race, but should we send this to
stable?

Reviewed-by: Jeff Layton <jlayton@kernel.org>