[PATCH] rxrpc: Call state should be read with READ_ONCE() under some circumstances

The call state may be changed at any time by the data-ready routine in
response to received packets, so if the call state is to be read and acted
upon several times in a function, READ_ONCE() must be used unless the call
state lock is held.

Signed-off-by: Baptiste Lepers <redacted>
---
 net/rxrpc/input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 667c44aa5a63..dc201363f2c4 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c

@@ -430,7 +430,7 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
 		return;
 	}
 
-	if (call->state == RXRPC_CALL_SERVER_RECV_REQUEST) {
+	if (state == RXRPC_CALL_SERVER_RECV_REQUEST) {
 		unsigned long timo = READ_ONCE(call->next_req_timo);
 		unsigned long now, expect_req_by;
 

-- 
2.17.1

Baptiste Lepers [off-list ref] wrote:

The call state may be changed at any time by the data-ready routine in
response to received packets, so if the call state is to be read and acted
upon several times in a function, READ_ONCE() must be used unless the call
state lock is held.

I'm going to add:

    As it happens, we used READ_ONCE() to read the state a few lines above the
    unmarked read in rxrpc_input_data(), so use that value rather than
    re-reading it.

to the commit message, if that's okay by you.

David

Yes, that's fine with me. Thanks for the clarification of the commit message.
(Sorry for the double send, I forgot to enable plain text on my
previous answer.)

Baptiste.

On Thu, Jan 7, 2021 at 10:05 PM David Howells [off-list ref] wrote:

Baptiste Lepers [off-list ref] wrote:

quoted

The call state may be changed at any time by the data-ready routine in
response to received packets, so if the call state is to be read and acted
upon several times in a function, READ_ONCE() must be used unless the call
state lock is held.

I'm going to add:

    As it happens, we used READ_ONCE() to read the state a few lines above the
    unmarked read in rxrpc_input_data(), so use that value rather than
    re-reading it.

to the commit message, if that's okay by you.

David