Re: [PATCH v2 1/2] seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested()

Tetsuo Handa
2023-06-26T09:26:33Z

On 2023/06/26 17:12, Sebastian Andrzej Siewior wrote:
> On 2023-06-24 15:54:12 [+0900], Tetsuo Handa wrote:
>> Why not to do the same on the end side?
>>
>> static inline void do_write_seqcount_end(seqcount_t *s)
>> {
>> - seqcount_release(&s->dep_map, _RET_IP_);
>> do_raw_write_seqcount_end(s);
>> + seqcount_release(&s->dep_map, _RET_IP_);
>> }
>
> I don't have a compelling argument for doing it. It is probably better
> to release the lock from lockdep's point of view and then really release
> it (so it can't be acquired before it is released).

We must do it because this is a source of possible printk() deadlock.
Otherwise, I will nack on PATCH 2/2.

>
> Looking at other locking primitives (spin_lock_unlock(),
> mutex_unlock(),…) that is what they do in the unlock path: lockdep
> annotation followed by the actual operation. Therefore I would keep the
> current ordering to remain in-sync with the other primitives.