[PATCH net v4 04/15] rxrpc: Fix call removal to use RCU safe deletion

[David Howells <dhowells@redhat.com>]

Fix rxrpc call removal from the rxnet->calls list to use list_del_rcu()
rather than list_del_init() to prevent stuffing up reading
/proc/net/rxrpc/calls from potentially getting into an infinite loop.

This, however, means that list_empty() no longer works on an entry that's
been deleted from the list, making it harder to detect prior deletion.  Fix
this by:

Firstly, make rxrpc_destroy_all_calls() only dump the first ten calls that
are unexpectedly still on the list.  Limiting the number of steps means
there's no need to call cond_resched() or to remove calls from the list
here, thereby eliminating the need for rxrpc_put_call() to check for that.

rxrpc_put_call() can then be fixed to unconditionally delete the call from
the list as it is the only place that the deletion occurs.

Closes: https://sashiko.dev/#/patchset/20260319150150.4189381-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Eric Dumazet <edumazet@google.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
cc: stable@kernel.org
---
 include/trace/events/rxrpc.h |  2 +-
 net/rxrpc/call_object.c      | 24 +++++++++---------------
 2 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 869f97c9bf73..a826cd80007b 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -347,7 +347,7 @@
 	EM(rxrpc_call_see_release,		"SEE release ") \
 	EM(rxrpc_call_see_userid_exists,	"SEE u-exists") \
 	EM(rxrpc_call_see_waiting_call,		"SEE q-conn  ") \
-	E_(rxrpc_call_see_zap,			"SEE zap     ")
+	E_(rxrpc_call_see_still_live,		"SEE !still-l")
 
 #define rxrpc_txqueue_traces \
 	EM(rxrpc_txqueue_await_reply,		"AWR") \
diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index 918f41d97a2f..59329cfe1532 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -654,11 +654,9 @@ void rxrpc_put_call(struct rxrpc_call *call, enum rxrpc_call_trace why)
 	if (dead) {
 		ASSERTCMP(__rxrpc_call_state(call), ==, RXRPC_CALL_COMPLETE);
 
-		if (!list_empty(&call->link)) {
-			spin_lock(&rxnet->call_lock);
-			list_del_init(&call->link);
-			spin_unlock(&rxnet->call_lock);
-		}
+		spin_lock(&rxnet->call_lock);
+		list_del_rcu(&call->link);
+		spin_unlock(&rxnet->call_lock);
 
 		rxrpc_cleanup_call(call);
 	}
@@ -730,24 +728,20 @@ void rxrpc_destroy_all_calls(struct rxrpc_net *rxnet)
 	_enter("");
 
 	if (!list_empty(&rxnet->calls)) {
-		spin_lock(&rxnet->call_lock);
+		int shown = 0;
 
-		while (!list_empty(&rxnet->calls)) {
-			call = list_entry(rxnet->calls.next,
-					  struct rxrpc_call, link);
-			_debug("Zapping call %p", call);
+		spin_lock(&rxnet->call_lock);
 
-			rxrpc_see_call(call, rxrpc_call_see_zap);
-			list_del_init(&call->link);
+		list_for_each_entry(call, &rxnet->calls, link) {
+			rxrpc_see_call(call, rxrpc_call_see_still_live);
 
 			pr_err("Call %p still in use (%d,%s,%lx,%lx)!\n",
 			       call, refcount_read(&call->ref),
 			       rxrpc_call_states[__rxrpc_call_state(call)],
 			       call->flags, call->events);
 
-			spin_unlock(&rxnet->call_lock);
-			cond_resched();
-			spin_lock(&rxnet->call_lock);
+			if (++shown >= 10)
+				break;
 		}
 
 		spin_unlock(&rxnet->call_lock);