[Devel] [PATCH VZ10 v3 0/4] connector: do not lose exit events for in-CT listeners

[Vasileios Almpanis <vasileios.almpanis@virtuozzo.com>]

The proc connector reports the exit event after exit_notify(), so the
parent may already have reaped the exiting task. release_task() ->
exit_ve_namespace() then resets tsk->task_ve to ve0, and if that wins
the race the event is delivered to the host listeners only. A listener
inside the container never sees the exit event. LTP catches this as the
flaky cn_pec exit-test failure causing the test to hang for as long as 8
hours on GCOV kernels.

Patch 4 fixes this by pinning the task's VE for the exit notification
before exit_notify(). This means the delivery path can now run against
a VE whose last task is already reaped, i.e. concurrently with the
per-VE connector teardown, which was impossible before. Patches 1-3
prepare for that: annotate ve->cn with __rcu, free the per-VE connector
state only after an RCU grace period, and deliver per-VE events under
rcu_read_lock().

Testing:
KASAN, PROVE_LOCKING/PROVE_RCU, DEBUG_OBJECTS, kmemleak=on; HCI VM with one
container):
 - LTP cn_pec inside a CT: unpatched kernel loses exit events in 3 of
   10 runs (-n 50); patched kernel passes 30 of 30 runs.
 - Teardown stress: 15 cycles of an active in-CT pec_listener plus a
   200-process exit storm with vzctl stop/start while events are in
   flight: no KASAN/lockdep/RCU splats, kmemleak scans report 0
   unreferenced objects.

https://virtuozzo.atlassian.net/browse/VSTOR-140421

---
Changes in v3:
- Patch 2: also make the netlink receive path safe against the VE stop.
  cn_call_callback() can be reached by a host task in the CT netns
  (e.g. nsenter) after ve->cn is cleared but before the kernel socket
  is released in cn_fini_ve(); look up the callback device and walk the
  queue under rcu_read_lock() and bail out on NULL (Konstantin).
- Patch 2: wait for an RCU grace period in the cn_init_ve() error path
  too before freeing ve->cn, since it is published early with
  rcu_assign_pointer(); symmetric to cn_proc_fini_ve(). This also
  covers the early-publish concern raised on patch 1.
- Link to v2: https://lists.openvz.org/pipermail/devel/2026-August/084616.html

Changes in v2:
- Turned the single patch into a series: with the exit event now
  delivered for a possibly already-reaped task, the per-VE delivery
  path can race with the connector teardown in cn_fini_ve(). New
  patches 1-3 make that safe: annotate ve->cn with __rcu, free the
  per-VE connector state only after an RCU grace period, and run the
  delivery under rcu_read_lock().
- cn_proc.h: forward-declare struct ve_struct instead of including
  linux/ve.h.
- Link to v1: https://lists.openvz.org/pipermail/devel/2026-August/084581.html

---
Vasileios Almpanis (4):
      connector: annotate ve->cn with __rcu
      connector: free the per-VE connector state after an RCU grace period
      connector: deliver per-VE proc events under an RCU read lock
      proc connector: pin task VE for the exit event notification

 drivers/connector/cn_proc.c   | 105 ++++++++++++++++++++++++++++++++++--------
 drivers/connector/connector.c |  70 ++++++++++++++++++++++------
 include/linux/cn_proc.h       |   8 +++-
 include/linux/ve.h            |   2 +-
 kernel/exit.c                 |   5 +-
 5 files changed, 153 insertions(+), 37 deletions(-)
---
base-commit: 1e648e17487b16486de22cefcd27672a454a1c3e
change-id: 20260813-connectors-3571be4ae57b

-- 
Best regards, Vasileios Almpanis
Software Developer, Virtuozzo.