Re: [RFC v7 11/19] lockdep: Fix recursive read lock related safe->unsafe detection

From: Qian Cai
Date: Wed Sep 16 2020 - 18:13:19 EST

On Thu, 2020-09-17 at 00:14 +0800, Boqun Feng wrote:
> Found a way to resolve this while still keeping the BFS. Every time when
> we want to enqueue a lock_list, we basically enqueue a whole dep list of
> entries from the previous lock_list, so we can use a trick here: instead
> enqueue all the entries, we only enqueue the first entry and we can
> fetch other silbing entries with list_next_or_null_rcu(). Patch as
> below, I also took the chance to clear the code up and add more
> comments. I could see this number (in /proc/lockdep_stats):
> max bfs queue depth: 201
> down to (after apply this patch)
> max bfs queue depth: 61
> with x86_64_defconfig along with lockdep and selftest configs.
> Qian, could you give it a try?

It works fine as the number went down from around 3000 to 500 on our workloads.