fix(section_list): add spinlock for free list and fix use-after-unmap

[0xfullex]

Summary

• Add pthread_spinlock to protect free list operations from race conditions
• Fix use-after-unmap bug in detach_article_block_shm()

Changes

Race Condition Fix (Free List)

Added pthread_spinlock_t free_list_spinlock to protect concurrent access to the article block free list:

1. pop_free_article_block(): Lock before accessing p_block_free_list, unlock after
2. push_free_article_block(): Lock before modifying p_block_free_list, unlock after

Spinlock is chosen over mutex because:

• Critical section is very short (only a few pointer operations)
• No blocking operations inside critical section
• Lower latency than mutex for short critical sections

Use-After-Unmap Fix

In detach_article_block_shm(), the code was accessing p_article_block_pool->shm_count and p_article_block_pool->shm_size after potentially unmapping memory. Fixed by:

1. Saving shm_count and shm_size to local variables before any unmap operations
2. Using saved values for loop iteration and final unmap

Lifecycle Management

• Initialize spinlock in article_block_init()
• Destroy spinlock in detach_article_block_shm()

Test Plan

• Compile verification
• Concurrent access testing with multiple processes
• Verify no memory leaks on cleanup

🤖 Generated with Claude Code

[leafok88]

pthread spinlock is not proper for this multi-process application.