[PATCH v4 01/11] SUNRPC: Assign a unique identifier to each svc_xprt

[Chuck Lever <cel@kernel.org>]

A consumer that associates state with a transport without holding a
reference cannot detect ABA collisions: once a transport is freed,
SLUB may hand out a new svc_xprt at the same address.

Assign each transport a 32-bit identifier from a global sequential
counter in svc_xprt_init(). An identifier is reused only after 2^32
further transports have been created, so a consumer whose
association is shorter-lived than that needs no release when the
transport is freed. The NFSD duplicate reply cache is the first
consumer. A 32-bit value fits the padding in its cache entry, and a
cache entry is retained for two minutes, not for 2^32 connections.

Assisted-by: LLM
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 include/linux/sunrpc/svc_xprt.h |  1 +
 include/trace/events/sunrpc.h   |  8 ++++++--
 net/sunrpc/svc_xprt.c           | 17 ++++++++++++++---
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index 2af222f3ea2c..9f940c892eca 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -56,6 +56,7 @@ struct svc_xprt {
 	struct svc_xprt_class	*xpt_class;
 	const struct svc_xprt_ops *xpt_ops;
 	struct kref		xpt_ref;
+	u32			xpt_id;
 	ktime_t			xpt_qtime;
 	struct list_head	xpt_list;
 	struct lwq_node		xpt_ready;
diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index ff855197880d..30d5fbb07e0a 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -1986,7 +1986,8 @@ TRACE_EVENT(svc_xprt_create_err,
 		__sockaddr(server, (x)->xpt_locallen) \
 		__sockaddr(client, (x)->xpt_remotelen) \
 		__field(unsigned long, flags) \
-		__field(unsigned int, netns_ino)
+		__field(unsigned int, netns_ino) \
+		__field(u32, xpt_id)
 
 #define SVC_XPRT_ENDPOINT_ASSIGNMENTS(x) \
 		do { \
@@ -1996,13 +1997,15 @@ TRACE_EVENT(svc_xprt_create_err,
 					  (x)->xpt_remotelen); \
 			__entry->flags = (x)->xpt_flags; \
 			__entry->netns_ino = (x)->xpt_net->ns.inum; \
+			__entry->xpt_id = (x)->xpt_id; \
 		} while (0)
 
 #define SVC_XPRT_ENDPOINT_FORMAT \
-		"server=%pISpc client=%pISpc flags=%s"
+		"server=%pISpc client=%pISpc xpt_id=%u flags=%s"
 
 #define SVC_XPRT_ENDPOINT_VARARGS \
 		__get_sockaddr(server), __get_sockaddr(client), \
+		__entry->xpt_id, \
 		show_svc_xprt_flags(__entry->flags)
 
 TRACE_EVENT(svc_xprt_enqueue,
@@ -2024,6 +2027,7 @@ TRACE_EVENT(svc_xprt_enqueue,
 				  xprt->xpt_remotelen);
 		__entry->flags = flags;
 		__entry->netns_ino = xprt->xpt_net->ns.inum;
+		__entry->xpt_id = xprt->xpt_id;
 	),
 
 	TP_printk(SVC_XPRT_ENDPOINT_FORMAT, SVC_XPRT_ENDPOINT_VARARGS)
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index d5634dd6d6cc..f836a7aebd64 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -26,6 +26,8 @@
 static unsigned int svc_rpc_per_connection_limit __read_mostly;
 module_param(svc_rpc_per_connection_limit, uint, 0644);
 
+static atomic_t svc_xprt_id_seq;
+
 
 static struct svc_deferred_req *svc_deferred_dequeue(struct svc_xprt *xprt);
 static int svc_deferred_recv(struct svc_rqst *rqstp);
@@ -190,9 +192,17 @@ void svc_xprt_put(struct svc_xprt *xprt)
 }
 EXPORT_SYMBOL_GPL(svc_xprt_put);
 
-/*
- * Called by transport drivers to initialize the transport independent
- * portion of the transport instance.
+/**
+ * svc_xprt_init - initialize transport-independent portion of a transport
+ * @net: network namespace in which the transport operates
+ * @xcl: transport class providing operations and metadata
+ * @xprt: svc_xprt to initialize
+ * @serv: RPC service that owns this transport
+ *
+ * @xprt->xpt_id is reused only after 2^32 further transports have
+ * been initialized.
+ *
+ * Context: Process context. May sleep.
  */
 void svc_xprt_init(struct net *net, struct svc_xprt_class *xcl,
 		   struct svc_xprt *xprt, struct svc_serv *serv)
@@ -210,6 +220,7 @@ void svc_xprt_init(struct net *net, struct svc_xprt_class *xcl,
 	set_bit(XPT_BUSY, &xprt->xpt_flags);
 	xprt->xpt_net = get_net_track(net, &xprt->ns_tracker, GFP_ATOMIC);
 	strcpy(xprt->xpt_remotebuf, "uninitialized");
+	xprt->xpt_id = atomic_inc_return(&svc_xprt_id_seq);
 }
 EXPORT_SYMBOL_GPL(svc_xprt_init);
 

-- 
2.55.0