fix(cmrpc): release session when resend exhaustion aborts the AR

[acrews42]

Symptom

After a few AR churn cycles (controller connects, then aborts or disappears without answering the device's CControl/ApplicationReady request), a p-net device starts logging

CMRPC(4331): Out of session resources for incoming frame.

for every incoming RPC frame and never recovers. New Connects are still accepted, but record writes and PrmEnd stall until the controller's RPC timeout, and the AR then aborts with CMSM: Timeout for communication start up (0xFD/0x06). The device is effectively wedged until restart. A stale scheduler handle from the leaked session also produces SCHEDULER: Invalid value 0 for timeout "(null)". No removal.

Root cause

In pf_cmrpc_send_with_timeout, when resend_counter is exhausted:

• the from_me == true branch (CControl request, no response) aborts the AR and closes the socket, but never calls pf_session_release;
• the fragment-timeout branch aborts the AR and releases nothing at all.

The session stays in_use forever. With PF_MAX_SESSION = 2 * PNET_MAX_AR + 1 — three sessions in the default single-AR configuration — a handful of unanswered CControls exhausts the pool permanently.

Fix

Call pf_session_release in both exhaustion branches, after the AR abort (mirroring the release the normal completion paths perform).

Testing

Reproduced with a PROFINET controller performing repeated connect/abort cycles against 32 p-net-based simulated devices (Linux, default options):

• Before: each device wedged after ~3 unanswered CControls; subsequent establish attempts crawled (30 s RPC recv timeouts per step) and a 32-device reconnect train that normally takes ~45 s blew past 480 s.
• After: three consecutive full 32-device reconnect cycles completed with flat establish times (40/41/40 s) and zero session-exhaustion log lines on sampled devices.

Happy to sign a CLA or rework the patch to your conventions if needed — this is also offered under the project's GPLv3 terms for the dual-license arrangement at your discretion.

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