linux-kernel - [PATCH net] rxrpc: Fix missing locking causing hanging calls

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Message-ID: <726660.1730898202@warthog.procyon.org.uk>
Date: Wed, 06 Nov 2024 13:03:22 +0000
From: David Howells <dhowells@...hat.com>
To: netdev@...r.kernel.org
cc: dhowells@...hat.com, Marc Dionne <marc.dionne@...istor.com>,
    "David S. Miller" <davem@...emloft.net>,
    Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
    Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
    linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH net] rxrpc: Fix missing locking causing hanging calls

If a call gets aborted (e.g. because kafs saw a signal) between it being
queued for connection and the I/O thread picking up the call, the abort
will be prioritised over the connection and it will be removed from
local->new_client_calls by rxrpc_disconnect_client_call() without a lock
being held.  This may cause other calls on the list to disappear if a race
occurs.

Fix this by taking the client_call_lock when removing a call from whatever
list its ->wait_link happens to be on.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Marc Dionne <marc.dionne@...istor.com>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: Simon Horman <horms@...nel.org>
cc: linux-afs@...ts.infradead.org
cc: netdev@...r.kernel.org
---
 include/trace/events/rxrpc.h |    1 +
 net/rxrpc/conn_client.c      |    4 ++++
 2 files changed, 5 insertions(+)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index c2f087e90fbe..d03e0bd8c028 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -287,6 +287,7 @@
 	EM(rxrpc_call_see_input,		"SEE input   ") \
 	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     ")
 
 #define rxrpc_txqueue_traces \
diff --git a/net/rxrpc/conn_client.c b/net/rxrpc/conn_client.c
index d25bf1cf3670..bb11e8289d6d 100644
--- a/net/rxrpc/conn_client.c
+++ b/net/rxrpc/conn_client.c
@@ -516,6 +516,7 @@ void rxrpc_connect_client_calls(struct rxrpc_local *local)
 
 		spin_lock(&local->client_call_lock);
 		list_move_tail(&call->wait_link, &bundle->waiting_calls);
+		rxrpc_see_call(call, rxrpc_call_see_waiting_call);
 		spin_unlock(&local->client_call_lock);
 
 		if (rxrpc_bundle_has_space(bundle))
@@ -586,7 +587,10 @@ void rxrpc_disconnect_client_call(struct rxrpc_bundle *bundle, struct rxrpc_call
 		_debug("call is waiting");
 		ASSERTCMP(call->call_id, ==, 0);
 		ASSERT(!test_bit(RXRPC_CALL_EXPOSED, &call->flags));
+		/* May still be on ->new_client_calls. */
+		spin_lock(&local->client_call_lock);
 		list_del_init(&call->wait_link);
+		spin_unlock(&local->client_call_lock);
 		return;
 	}