[PATCH v2 3/3] SUNRPC: Destroy the back channel when we destroy the host transport

[Trond Myklebust <trondmy@gmail.com>]

When we're destroying the host transport mechanism, we should ensure
that we do not leak memory by failing to release any back channel
slots that might still exist.

Reported-by: Neil Brown <neilb@suse.de>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 include/linux/sunrpc/bc_xprt.h | 5 +++++
 net/sunrpc/backchannel_rqst.c  | 2 +-
 net/sunrpc/xprt.c              | 5 +++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/linux/sunrpc/bc_xprt.h b/include/linux/sunrpc/bc_xprt.h
index 87d27e13d885..d796058cdff2 100644
--- a/include/linux/sunrpc/bc_xprt.h
+++ b/include/linux/sunrpc/bc_xprt.h
@@ -64,6 +64,11 @@ static inline int xprt_setup_backchannel(struct rpc_xprt *xprt,
 	return 0;
 }
 
+static inline void xprt_destroy_backchannel(struct rpc_xprt *xprt,
+					    unsigned int max_reqs)
+{
+}
+
 static inline bool svc_is_backchannel(const struct svc_rqst *rqstp)
 {
 	return false;
diff --git a/net/sunrpc/backchannel_rqst.c b/net/sunrpc/backchannel_rqst.c
index 7eb251372f94..195b40c5dae4 100644
--- a/net/sunrpc/backchannel_rqst.c
+++ b/net/sunrpc/backchannel_rqst.c
@@ -220,7 +220,7 @@ void xprt_destroy_bc(struct rpc_xprt *xprt, unsigned int max_reqs)
 		goto out;
 
 	spin_lock_bh(&xprt->bc_pa_lock);
-	xprt->bc_alloc_max -= max_reqs;
+	xprt->bc_alloc_max -= min(max_reqs, xprt->bc_alloc_max);
 	list_for_each_entry_safe(req, tmp, &xprt->bc_pa_list, rq_bc_pa_list) {
 		dprintk("RPC:        req=%p\n", req);
 		list_del(&req->rq_bc_pa_list);
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 8a45b3ccc313..41df4c507193 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1942,6 +1942,11 @@ static void xprt_destroy_cb(struct work_struct *work)
 	rpc_destroy_wait_queue(&xprt->sending);
 	rpc_destroy_wait_queue(&xprt->backlog);
 	kfree(xprt->servername);
+	/*
+	 * Destroy any existing back channel
+	 */
+	xprt_destroy_backchannel(xprt, UINT_MAX);
+
 	/*
 	 * Tear down transport state and free the rpc_xprt
 	 */
-- 
2.21.0