[PATCH mptcp-next] mptcp: update misleading comments.

[PATCH mptcp-next] mptcp: update misleading comments.

[Paolo Abeni]

The MPTCP data path is quite complex and hard to understend even
without some foggy comments referring to modified code and/or
completely misleading from the beginning.

Update a few of them to more accurately describing the current
status.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/protocol.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index c99eb4ce948e..8feb684408f7 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -662,9 +662,9 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 
 		skb = skb_peek(&ssk->sk_receive_queue);
 		if (!skb) {
-			/* if no data is found, a racing workqueue/recvmsg
-			 * already processed the new data, stop here or we
-			 * can enter an infinite loop
+			/* With racing move_skbs_to_msk() and __mptcp_move_skbs(),
+			 * a different CPU can have already processed the pending
+			 * data, stop here or we can enter an infinite loop
 			 */
 			if (!moved)
 				done = true;
@@ -672,9 +672,9 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 		}
 
 		if (__mptcp_check_fallback(msk)) {
-			/* if we are running under the workqueue, TCP could have
-			 * collapsed skbs between dummy map creation and now
-			 * be sure to adjust the size
+			/* Under fallback skbs have no MPTCP extension and TCP could
+			 * collapse them between the dummy map creation and the
+			 * current dequeue. Be sure to adjust the map size.
 			 */
 			map_remaining = skb->len;
 			subflow->map_data_len = skb->len;
@@ -3767,7 +3767,7 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock,
 	if (sk->sk_shutdown & RCV_SHUTDOWN)
 		mask |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP;
 
-	/* This barrier is coupled with smp_wmb() in tcp_reset() */
+	/* This barrier is coupled with smp_wmb() in __mptcp_error_report() */
 	smp_rmb();
 	if (sk->sk_err)
 		mask |= EPOLLERR;
-- 
2.37.3

Re: mptcp: update misleading comments.: Tests Results

[MPTCP CI]

Hi Paolo,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal:
  - Unstable: 2 failed test(s): packetdrill_add_addr selftest_mptcp_join 🔴:
  - Task: https://cirrus-ci.com/task/6420352380174336
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/6420352380174336/summary/summary.txt

- KVM Validation: debug:
  - Success! ✅:
  - Task: https://cirrus-ci.com/task/5012977496621056
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/5012977496621056/summary/summary.txt

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/d9dfe29d53ec


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-debug

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (Tessares)

Re: [PATCH mptcp-next] mptcp: update misleading comments.

[Mat Martineau]

On Mon, 26 Sep 2022, Paolo Abeni wrote:

> The MPTCP data path is quite complex and hard to understend even
> without some foggy comments referring to modified code and/or
> completely misleading from the beginning.
>
> Update a few of them to more accurately describing the current
> status.
>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Thanks for updating the comments, Paolo. New comments look good to me:

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>


> ---
> net/mptcp/protocol.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index c99eb4ce948e..8feb684408f7 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -662,9 +662,9 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
>
> 		skb = skb_peek(&ssk->sk_receive_queue);
> 		if (!skb) {
> -			/* if no data is found, a racing workqueue/recvmsg
> -			 * already processed the new data, stop here or we
> -			 * can enter an infinite loop
> +			/* With racing move_skbs_to_msk() and __mptcp_move_skbs(),
> +			 * a different CPU can have already processed the pending
> +			 * data, stop here or we can enter an infinite loop
> 			 */
> 			if (!moved)
> 				done = true;
> @@ -672,9 +672,9 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
> 		}
>
> 		if (__mptcp_check_fallback(msk)) {
> -			/* if we are running under the workqueue, TCP could have
> -			 * collapsed skbs between dummy map creation and now
> -			 * be sure to adjust the size
> +			/* Under fallback skbs have no MPTCP extension and TCP could
> +			 * collapse them between the dummy map creation and the
> +			 * current dequeue. Be sure to adjust the map size.
> 			 */
> 			map_remaining = skb->len;
> 			subflow->map_data_len = skb->len;
> @@ -3767,7 +3767,7 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock,
> 	if (sk->sk_shutdown & RCV_SHUTDOWN)
> 		mask |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP;
>
> -	/* This barrier is coupled with smp_wmb() in tcp_reset() */
> +	/* This barrier is coupled with smp_wmb() in __mptcp_error_report() */
> 	smp_rmb();
> 	if (sk->sk_err)
> 		mask |= EPOLLERR;
> -- 
> 2.37.3
>
>
>

--
Mat Martineau
Intel

Re: mptcp: update misleading comments.: Tests Results

[MPTCP CI]

Hi Paolo,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal:
  - Unstable: 2 failed test(s): selftest_mptcp_join selftest_simult_flows 🔴:
  - Task: https://cirrus-ci.com/task/4956489147219968
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/4956489147219968/summary/summary.txt

- KVM Validation: debug:
  - Unstable: 1 failed test(s): packetdrill_add_addr 🔴:
  - Task: https://cirrus-ci.com/task/6082389054062592
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/6082389054062592/summary/summary.txt

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/2474bd2962c4


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-debug

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (Tessares)

Re: mptcp: update misleading comments.: Tests Results

[Matthieu Baerts]

Hi Davide,

Please see below: it looks like Patchew is re-creating tags again after
someone sends a Reviewed-by, etc.

Yesterday, Mat sent its RvB tag and you can see it has been added in the
commit that has been tested here:

https://github.com/multipath-tcp/mptcp_net-next/commit/2474bd2962c4

Do you see what to change to avoid this? :)

Cheers,
Matt

On 27/09/2022 01:07, MPTCP CI wrote:
> Hi Paolo,
> 
> Thank you for your modifications, that's great!
> 
> Our CI did some validations and here is its report:
> 
> - KVM Validation: normal:
>   - Unstable: 2 failed test(s): selftest_mptcp_join selftest_simult_flows 🔴:
>   - Task: https://cirrus-ci.com/task/4956489147219968
>   - Summary: https://api.cirrus-ci.com/v1/artifact/task/4956489147219968/summary/summary.txt
> 
> - KVM Validation: debug:
>   - Unstable: 1 failed test(s): packetdrill_add_addr 🔴:
>   - Task: https://cirrus-ci.com/task/6082389054062592
>   - Summary: https://api.cirrus-ci.com/v1/artifact/task/6082389054062592/summary/summary.txt
> 
> Initiator: Patchew Applier
> Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/2474bd2962c4
> 
> 
> If there are some issues, you can reproduce them using the same environment as
> the one used by the CI thanks to a docker image, e.g.:
> 
>     $ cd [kernel source code]
>     $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
>         --pull always mptcp/mptcp-upstream-virtme-docker:latest \
>         auto-debug
> 
> For more details:
> 
>     https://github.com/multipath-tcp/mptcp-upstream-virtme-docker
> 
> 
> Please note that despite all the efforts that have been already done to have a
> stable tests suite when executed on a public CI like here, it is possible some
> reported issues are not due to your modifications. Still, do not hesitate to
> help us improve that ;-)
> 
> Cheers,
> MPTCP GH Action bot
> Bot operated by Matthieu Baerts (Tessares)
> 

-- 
Tessares | Belgium | Hybrid Access Solutions
www.tessares.net

Re: [PATCH mptcp-next] mptcp: update misleading comments.

[Matthieu Baerts]

Hi Paolo, Mat,

On 26/09/2022 17:27, Paolo Abeni wrote:
> The MPTCP data path is quite complex and hard to understend even
> without some foggy comments referring to modified code and/or
> completely misleading from the beginning.
> 
> Update a few of them to more accurately describing the current
> status.

Good idea, thank you for the patch and the review!

Now in our tree (feat. for net-next) with Mat's RvB tag:

New patches for t/upstream:
- 2bf3d5448679: mptcp: update misleading comments.
- Results: 676709a1f80b..34c4fe0fbc95 (export)


Tests are now in progress:

https://cirrus-ci.com/github/multipath-tcp/mptcp_net-next/export/20220927T075707

Cheers,
Matt
-- 
Tessares | Belgium | Hybrid Access Solutions
www.tessares.net