Re: [RFC PATCH v5] ntfs: serialize attribute-list replacement with lookups

[Hyunchul Lee]

Hi Cen,

This approach introduces too many changes. I apologize as I originally
recommended this design.

Therefore, I am now considering alternative approaches:

Design A:
  * Eliminates the raw pointer (ctx->al_entry) entirely from search_ctx.
  * Instead, it tracks the cursor using 'al_cursor.off' (offset within
    the buffer) and 'al_cursor.gen' (generation counter matching
    base_ni->attr_list_gen).
  * If the generation counter changes, the lookup detects this and
    restarts safely using an exact search key (al_exact).
  * Since we no longer carry raw pointers, attr_list_lock only needs to
    be held briefly during in-memory list operations.
  * To strictly maintain the lock order (runlist.lock -> attr_list_lock)
    and prevent deadlocks, functions that previously held attr_list_lock
    while calling runlist-locking operations must be refactored.
  * Pros:
    - Short-lived locks.
    - Narrow lock scope makes it easy to maintain codes.
  * Cons:
    - More complex implementation.

Design B (runlist.lock style):
  * Retains ctx->al_entry (raw pointers), but manages attr_list_lock as
    a top-level coarse-grained lock similar to runlist.lock.
  * We must establish a strict global lock hierarchy: runlist.lock ->
    attr_list_lock.
  * Pros:
    - Simpler implementation.
  * Cons:
    - Could reduce performance.
    - Wide lock scope makes it difficult to maintain codes.
    - May introduce a lot of '_nolock' helper functions to avoid
      self-deadlock.

Which approaches do you think would be better, or other approaches?
And please let me know if you would like me to implement it.