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Message-ID: <5b07e47d33925128400559f6c5eef694a9984279.camel@kernel.org>
Subject: Re: [PATCH 2/3] NFSD: restore delegation's sc_count if nfsd4_run_cb
 fails
From: Jeff Layton <jlayton@kernel.org>
To: Dai Ngo <dai.ngo@oracle.com>, chuck.lever@oracle.com
Cc: linux-nfs@vger.kernel.org, linux-nfs@stwm.de
Date: Fri, 15 Dec 2023 14:42:44 -0500
In-Reply-To: <1702667703-17978-3-git-send-email-dai.ngo@oracle.com>
References: <1702667703-17978-1-git-send-email-dai.ngo@oracle.com>
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On Fri, 2023-12-15 at 11:15 -0800, Dai Ngo wrote:
> Under some load conditions the callback work request can not be queued
> and nfsd4_run_cb returns 0 to caller. When this happens, the sc_count
> of the delegation state was left with an extra reference count preventing
> the state to be freed later.
>=20
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/nfsd/nfs4state.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
>=20
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 40415929e2ae..175f3e9f5822 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -2947,8 +2947,14 @@ void nfs4_cb_getattr(struct nfs4_cb_fattr *ncf)
> =20
>  	if (test_and_set_bit(CB_GETATTR_BUSY, &ncf->ncf_cb_flags))
>  		return;
> +
>  	refcount_inc(&dp->dl_stid.sc_count);
> -	nfsd4_run_cb(&ncf->ncf_getattr);
> +	if (!nfsd4_run_cb(&ncf->ncf_getattr)) {
> +		refcount_dec(&dp->dl_stid.sc_count);
> +		clear_bit(CB_GETATTR_BUSY, &ncf->ncf_cb_flags);
> +		wake_up_bit(&ncf->ncf_cb_flags, CB_GETATTR_BUSY);
> +		WARN_ON_ONCE(1);
> +	}
>  }
> =20
>  static struct nfs4_client *create_client(struct xdr_netobj name,
> @@ -4967,7 +4973,10 @@ static void nfsd_break_one_deleg(struct nfs4_deleg=
ation *dp)
>  	 * we know it's safe to take a reference.
>  	 */
>  	refcount_inc(&dp->dl_stid.sc_count);
> -	WARN_ON_ONCE(!nfsd4_run_cb(&dp->dl_recall));
> +	if (!nfsd4_run_cb(&dp->dl_recall)) {
> +		refcount_dec(&dp->dl_stid.sc_count);
> +		WARN_ON_ONCE(1);
> +	}
>  }
> =20
>  /* Called from break_lease() with flc_lock held. */
> @@ -8543,12 +8552,12 @@ nfsd4_deleg_getattr_conflict(struct svc_rqst *rqs=
tp, struct inode *inode,
>  				return 0;
>  			}
>  break_lease:
> -			spin_unlock(&ctx->flc_lock);
>  			nfsd_stats_wdeleg_getattr_inc();
> -
>  			dp =3D fl->fl_owner;
>  			ncf =3D &dp->dl_cb_fattr;
>  			nfs4_cb_getattr(&dp->dl_cb_fattr);
> +			spin_unlock(&ctx->flc_lock);
> +

The other hunks in this patch make sense, but what's going on here with
moving the lock down? Do we really need to hold the spinlock there? If
so, I would have expected to see an explanation in the changelog.

>  			wait_on_bit(&ncf->ncf_cb_flags, CB_GETATTR_BUSY, TASK_INTERRUPTIBLE);
>  			if (ncf->ncf_cb_status) {
>  				status =3D nfserrno(nfsd_open_break_lease(inode, NFSD_MAY_READ));

--=20
Jeff Layton <jlayton@kernel.org>