afs: Fix access after dec in put functions

Reference-putting functions should not access the object being put after
decrementing the refcount unless they reduce the refcount to zero.

Fix a couple of instances of this in afs by copying the information to be
logged by tracepoint to local variables before doing the decrement.

[Fixed a bit in afs_put_server() that I'd missed but Marc caught]

Fixes: 341f741 ("afs: Refcount the afs_call struct")
Fixes: 4521819 ("afs: Trace afs_server usage")
Fixes: 977e5f8 ("afs: Split the usage count on struct afs_server")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/165911278430.3745403.16526310736054780645.stgit@warthog.procyon.org.uk/ # v1

fs/afs/cmservice.c

@@ -212,7 +212,7 @@ static void SRXAFSCB_CallBack(struct work_struct *work)
 	 * to maintain cache coherency.
 	 */
 	if (call->server) {
-		trace_afs_server(call->server,
+		trace_afs_server(call->server->debug_id,
 				 refcount_read(&call->server->ref),
 				 atomic_read(&call->server->active),
 				 afs_server_trace_callback);

fs/afs/rxrpc.c

@@ -152,7 +152,7 @@ static struct afs_call *afs_alloc_call(struct afs_net *net,
 	call->iter = &call->def_iter;
 
 	o = atomic_inc_return(&net->nr_outstanding_calls);
-	trace_afs_call(call, afs_call_trace_alloc, 1, o,
+	trace_afs_call(call->debug_id, afs_call_trace_alloc, 1, o,
 		       __builtin_return_address(0));
 	return call;
 }
@@ -163,12 +163,13 @@ static struct afs_call *afs_alloc_call(struct afs_net *net,
 void afs_put_call(struct afs_call *call)
 {
 	struct afs_net *net = call->net;
+	unsigned int debug_id = call->debug_id;
 	bool zero;
 	int r, o;
 
 	zero = __refcount_dec_and_test(&call->ref, &r);
 	o = atomic_read(&net->nr_outstanding_calls);
-	trace_afs_call(call, afs_call_trace_put, r - 1, o,
+	trace_afs_call(debug_id, afs_call_trace_put, r - 1, o,
 		       __builtin_return_address(0));
 
 	if (zero) {
@@ -186,7 +187,7 @@ void afs_put_call(struct afs_call *call)
 		afs_put_addrlist(call->alist);
 		kfree(call->request);
 
-		trace_afs_call(call, afs_call_trace_free, 0, o,
+		trace_afs_call(call->debug_id, afs_call_trace_free, 0, o,
 			       __builtin_return_address(0));
 		kfree(call);
 
@@ -203,7 +204,7 @@ static struct afs_call *afs_get_call(struct afs_call *call,
 
 	__refcount_inc(&call->ref, &r);
 
-	trace_afs_call(call, why, r + 1,
+	trace_afs_call(call->debug_id, why, r + 1,
 		       atomic_read(&call->net->nr_outstanding_calls),
 		       __builtin_return_address(0));
 	return call;
@@ -677,7 +678,7 @@ static void afs_wake_up_async_call(struct sock *sk, struct rxrpc_call *rxcall,
 	call->need_attention = true;
 
 	if (__refcount_inc_not_zero(&call->ref, &r)) {
-		trace_afs_call(call, afs_call_trace_wake, r + 1,
+		trace_afs_call(call->debug_id, afs_call_trace_wake, r + 1,
 			       atomic_read(&call->net->nr_outstanding_calls),
 			       __builtin_return_address(0));
 

fs/afs/server.c

@@ -243,7 +243,7 @@ static struct afs_server *afs_alloc_server(struct afs_cell *cell,
 	server->rtt = UINT_MAX;
 
 	afs_inc_servers_outstanding(net);
-	trace_afs_server(server, 1, 1, afs_server_trace_alloc);
+	trace_afs_server(server->debug_id, 1, 1, afs_server_trace_alloc);
 	_leave(" = %p", server);
 	return server;
 
@@ -352,10 +352,12 @@ void afs_servers_timer(struct timer_list *timer)
 struct afs_server *afs_get_server(struct afs_server *server,
 				  enum afs_server_trace reason)
 {
+	unsigned int a;
 	int r;
 
 	__refcount_inc(&server->ref, &r);
-	trace_afs_server(server, r + 1, atomic_read(&server->active), reason);
+	a = atomic_read(&server->active);
+	trace_afs_server(server->debug_id, r + 1, a, reason);
 	return server;
 }
 
@@ -372,7 +374,7 @@ static struct afs_server *afs_maybe_use_server(struct afs_server *server,
 		return NULL;
 
 	a = atomic_inc_return(&server->active);
-	trace_afs_server(server, r + 1, a, reason);
+	trace_afs_server(server->debug_id, r + 1, a, reason);
 	return server;
 }
 
@@ -387,7 +389,7 @@ struct afs_server *afs_use_server(struct afs_server *server, enum afs_server_tra
 	__refcount_inc(&server->ref, &r);
 	a = atomic_inc_return(&server->active);
 
-	trace_afs_server(server, r + 1, a, reason);
+	trace_afs_server(server->debug_id, r + 1, a, reason);
 	return server;
 }
 
@@ -397,14 +399,16 @@ struct afs_server *afs_use_server(struct afs_server *server, enum afs_server_tra
 void afs_put_server(struct afs_net *net, struct afs_server *server,
 		    enum afs_server_trace reason)
 {
+	unsigned int a, debug_id = server->debug_id;
 	bool zero;
 	int r;
 
 	if (!server)
 		return;
 
+	a = atomic_inc_return(&server->active);
 	zero = __refcount_dec_and_test(&server->ref, &r);
-	trace_afs_server(server, r - 1, atomic_read(&server->active), reason);
+	trace_afs_server(debug_id, r - 1, a, reason);
 	if (unlikely(zero))
 		__afs_put_server(net, server);
 }
@@ -441,7 +445,7 @@ static void afs_server_rcu(struct rcu_head *rcu)
 {
 	struct afs_server *server = container_of(rcu, struct afs_server, rcu);
 
-	trace_afs_server(server, refcount_read(&server->ref),
+	trace_afs_server(server->debug_id, refcount_read(&server->ref),
 			 atomic_read(&server->active), afs_server_trace_free);
 	afs_put_addrlist(rcu_access_pointer(server->addresses));
 	kfree(server);
@@ -492,7 +496,7 @@ static void afs_gc_servers(struct afs_net *net, struct afs_server *gc_list)
 
 		active = atomic_read(&server->active);
 		if (active == 0) {
-			trace_afs_server(server, refcount_read(&server->ref),
+			trace_afs_server(server->debug_id, refcount_read(&server->ref),
 					 active, afs_server_trace_gc);
 			next = rcu_dereference_protected(
 				server->uuid_next, lockdep_is_held(&net->fs_lock.lock));
@@ -558,7 +562,7 @@ void afs_manage_servers(struct work_struct *work)
 		_debug("manage %pU %u", &server->uuid, active);
 
 		if (purging) {
-			trace_afs_server(server, refcount_read(&server->ref),
+			trace_afs_server(server->debug_id, refcount_read(&server->ref),
 					 active, afs_server_trace_purging);
 			if (active != 0)
 				pr_notice("Can't purge s=%08x\n", server->debug_id);
@@ -638,7 +642,7 @@ static noinline bool afs_update_server_record(struct afs_operation *op,
 
 	_enter("");
 
-	trace_afs_server(server, refcount_read(&server->ref),
+	trace_afs_server(server->debug_id, refcount_read(&server->ref),
 			 atomic_read(&server->active),
 			 afs_server_trace_update);
 

include/trace/events/afs.h

@@ -727,10 +727,10 @@ TRACE_EVENT(afs_cb_call,
 	    );
 
 TRACE_EVENT(afs_call,
-	    TP_PROTO(struct afs_call *call, enum afs_call_trace op,
+	    TP_PROTO(unsigned int call_debug_id, enum afs_call_trace op,
 		     int ref, int outstanding, const void *where),
 
-	    TP_ARGS(call, op, ref, outstanding, where),
+	    TP_ARGS(call_debug_id, op, ref, outstanding, where),
 
 	    TP_STRUCT__entry(
 		    __field(unsigned int,		call		)
@@ -741,7 +741,7 @@ TRACE_EVENT(afs_call,
 			     ),
 
 	    TP_fast_assign(
-		    __entry->call = call->debug_id;
+		    __entry->call = call_debug_id;
 		    __entry->op = op;
 		    __entry->ref = ref;
 		    __entry->outstanding = outstanding;
@@ -1433,10 +1433,10 @@ TRACE_EVENT(afs_cb_miss,
 	    );
 
 TRACE_EVENT(afs_server,
-	    TP_PROTO(struct afs_server *server, int ref, int active,
+	    TP_PROTO(unsigned int server_debug_id, int ref, int active,
 		     enum afs_server_trace reason),
 
-	    TP_ARGS(server, ref, active, reason),
+	    TP_ARGS(server_debug_id, ref, active, reason),
 
 	    TP_STRUCT__entry(
 		    __field(unsigned int,		server		)
@@ -1446,7 +1446,7 @@ TRACE_EVENT(afs_server,
 			     ),
 
 	    TP_fast_assign(
-		    __entry->server = server->debug_id;
+		    __entry->server = server_debug_id;
 		    __entry->ref = ref;
 		    __entry->active = active;
 		    __entry->reason = reason;