Hello. 홍신 shin hong wrote:
Hi. I have a question on lock ordering while I read ReiserFS code in Linux 2.6.30.4. At write_ordered_buffers() function in reiserfs/journal.c, What is the lock ordering between spin_lock(lock) and lock_buffer(bh)? It seems that the lock ordering between spin_lock(lock) and lock_buffer(bh) is inconsistent. At line 858, the lock ordering is spin_lock(lock) → lock_buffer(bh).
Nup, at line 858 we have trylock_buffer, which is not the same as lock_buffer: in our case the process won't wait for the lock to be released.
However, at line 881, lock_buffer(bh) → spin_lock(lock) since add_to_chunk() releases and re-takes spin_lock(lock). Is it necessary that the ordering between two locks is consistent?
This is sufficient, but not necessary condition to prevent deadlock. However, breaking a lock ordering is ugly, and you will need to defend every such case explaining why there is no way to keep the ordering, and writing a lot of (unclear) comments why the deadlock is impossible :) -- To unsubscribe from this list: send the line "unsubscribe reiserfs-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
