Re: [PATCH 3/3] pnfs-submit: callbacks cannot use an nfs_client that is being freed

[Benny Halevy <bhalevy@panasas.com>]

On 2010-11-11 16:10, andros@netapp.com wrote:
> From: Andy Adamson <andros@netapp.com>
> 
> Guarantee that the nfs_client exists when referenced to by callback processing
> by not procssing callbacks on an nfs_client in the process of being freed.
> 
> Signed-off-by: Andy Adamson <andros@netapp.com>
> ---
>  fs/nfs/client.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/client.c b/fs/nfs/client.c
> index dbf43e7..86657ee 100644
> --- a/fs/nfs/client.c
> +++ b/fs/nfs/client.c
> @@ -392,7 +392,9 @@ struct nfs_client *nfs_find_client(const struct sockaddr *addr, u32 nfsversion)
>  		if (!nfs_sockaddr_match_ipaddr(addr, clap))
>  			continue;
>  
> -		atomic_inc(&clp->cl_count);
> +		/* Don't return an nfs_client that is being freed */
> +		if (!atomic_inc_not_zero(&clp->cl_count))
> +			continue;
>  		spin_unlock(&nfs_client_lock);
>  		return clp;
>  	}
> @@ -425,7 +427,9 @@ struct nfs_client *nfs_find_client_next(struct nfs_client *clp)
>  		if (!nfs_sockaddr_match_ipaddr(sap, clap))
>  			continue;
>  
> -		atomic_inc(&clp->cl_count);
> +		/* Don't return an nfs_client that is being freed */
> +		if (!atomic_inc_not_zero(&clp->cl_count))
> +			continue;
>  		spin_unlock(&nfs_client_lock);
>  		return clp;
>  	}

Hmm, nfs_put_client deletes the client when cl_count reaches zero
so how can cl_count be zero while clp is listed?

Benny

In put_nfs_client