Re: [next:akpm 147/308] net/sunrpc/clnt.c:720:36: sparse: dereference of noderef expression

[Mel Gorman <mgorman@suse.de>]

On Fri, Jul 27, 2012 at 09:02:25PM +0800, Fengguang Wu wrote:
> Hi Mel,
> 
> There are new sparse warnings show up in
> 
> tree:   git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git akpm
> head:   247109fa112ac912f31efc28e130ed2a0cc1764c
> commit: 5bb176c86a868289d5d93d89919c3b5a339d6d20 [147/308] nfs: enable swap on NFS
> 

Thanks (adding Andrew to cc for picking up in mm)

How about the following?

---8<---

sparsefix: nfs: enable swap on NFS

Fengguang Wu reports the following sparse problem

	net/sunrpc/clnt.c:720:36: sparse: dereference of noderef expression

task->tk_client->cl_xprt is RCU protected and must be dereferenced using
rcu_dereference(). This patch checks if a socket is being used for swap
and if so it takes the RCU read lock and dereferences properly. This is
a fix for "nfs: enable swap on NFS"

Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 net/sunrpc/clnt.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 2848e5b..df27890 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -717,8 +717,15 @@ void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt)
 		atomic_inc(&clnt->cl_count);
 		if (clnt->cl_softrtry)
 			task->tk_flags |= RPC_TASK_SOFT;
-		if (task->tk_client->cl_xprt->swapper)
-			task->tk_flags |= RPC_TASK_SWAPPER;
+		if (sk_memalloc_socks()) {
+			struct rpc_xprt *xprt;
+
+			rcu_read_lock();
+			xprt = rcu_dereference(clnt->cl_xprt);
+			if (xprt->swapper)
+				task->tk_flags |= RPC_TASK_SWAPPER;
+			rcu_read_unlock();
+		}
 		/* Add to the client's list of all tasks */
 		spin_lock(&clnt->cl_lock);
 		list_add_tail(&task->tk_task, &clnt->cl_tasks);