Date:   Tue, 30 Nov 2021 14:52:50 -0800
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     linux-nfs@vger.kernel.org
Subject: Re: [PATCH v2] NFSD: Fix RCU-related sparse splat
Message-ID: <20211130225250.GC641268@paulmck-ThinkPad-P17-Gen-1>
Reply-To: paulmck@kernel.org
References: <163821156142.90770.4019362941494014139.stgit@bazille.1015granger.net>
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On Mon, Nov 29, 2021 at 01:46:07PM -0500, Chuck Lever wrote:
> To address this error:
> 
>   CC [M]  fs/nfsd/filecache.o
>   CHECK   /home/cel/src/linux/linux/fs/nfsd/filecache.c
> /home/cel/src/linux/linux/fs/nfsd/filecache.c:772:9: error: incompatible types in comparison expression (different address spaces):
> /home/cel/src/linux/linux/fs/nfsd/filecache.c:772:9:    struct net [noderef] __rcu *
> /home/cel/src/linux/linux/fs/nfsd/filecache.c:772:9:    struct net *
> 
> The "net" field in struct nfsd_fcache_disposal is not annotated as
> requiring an RCU assignment, so replace the macro that includes an
> invocation of rcu_check_sparse() with an equivalent that does not.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

From an RCU perspective:

Acked-by: Paul E. McKenney <paulmck@kernel.org>

But it would be good to get someone more familiar with the code to
look at this.

							Thanx, Paul

> ---
>  fs/nfsd/filecache.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index fdf89fcf1a0c..3b172eda0e9a 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -772,7 +772,7 @@ nfsd_alloc_fcache_disposal(struct net *net)
>  static void
>  nfsd_free_fcache_disposal(struct nfsd_fcache_disposal *l)
>  {
> -	rcu_assign_pointer(l->net, NULL);
> +	WRITE_ONCE(l->net, NULL);
>  	cancel_work_sync(&l->work);
>  	nfsd_file_dispose_list(&l->freeme);
>  	kfree_rcu(l, rcu);
>