Re: [PATCH v1 07/12] f2fs: cache: use node cache

[Wenjie Qi]

Hi Chao,

> entry = fn->entry;
> f2fs_cache_get(entry);
> spin_unlock_irqrestore(&sbi->fsync_node_lock, flags);
>
> f2fs_cache_wait_writeback(entry);

The entry reference keeps the entry allocated, but the waiter does not hold
the entry lock.  After WRITEBACK is cleared, invalidation can detach the
entry and set `entry->cache` to NULL.  `f2fs_cache_wait_writeback()` checks
and uses `entry->cache` through separate accesses.

Does the reference taken here also guarantee that the parent cache remains
attached across the wait helper's check and use?