lua-lsm: fix unregister and module lifetime handling

[chenzongyao200127]

Lua-LSM module unregister has to coordinate several lifetimes at once: the global module list protected by modules_ss SRCU, per-VM loaded module references, shared dictionaries cached in Lua userdata, and the contexts where VM teardown is allowed to run.

This series keeps those pieces ordered so unregister no longer frees state that can still be reached from an existing Lua VM, and so lazy unload can finish modules once the last VM-local reference is gone.

The series contains these commits:

• lua-lsm: wait for SRCU readers before freeing module
• lua-lsm: fix shared dict lifetime on unregister
• lua-lsm: avoid leaking shared dict refs on userdata failure
• lua-lsm: avoid Lua teardown from task_call_func
• lua-lsm: finalize drained modules after lazy unload

Main fixes:

• Wait for modules_ss SRCU readers before freeing an unregistered module.
• Keep shared dictionaries refcounted while Lua userdata can still access them.
• Tombstone shared dictionaries at unregister so new lookups fail cleanly.
• Avoid taking shared-dict references before userdata exists to release them.
• Stop running Lua VM teardown through task_call_func(), which can execute under task/runqueue locks.
• Let non-current task VMs purge unloading modules lazily on their next Lua-LSM entry.
• Queue final teardown for zombie modules once lazy purge drains nloaded to zero.

Please use Rebase and merge, or another merge mode that preserves the individual commits. Please do not squash this PR, since each commit has its own kernel-style subject and message.

Validation:

• ./scripts/checkpatch.pl --git origin/lua-lsm..lua-lsm-unregister-lifetime-fixes
• git diff --check origin/lua-lsm..lua-lsm-unregister-lifetime-fixes

Signed-off-by: Zongyao Chen ZongYao.Chen@linux.alibaba.com

[chenzongyao200127]

The changes involved in this PR are kind of complex. I will add reproduction steps that clearly demonstrate the issues with the original implementation to prove its necessity.