Re: [PATCH 2/4] io_uring: switch deferred task_work to an io_wq_work_list

[Jens Axboe <axboe@kernel.dk>]

On 3/27/24 9:45 AM, Jens Axboe wrote:
>> smp_mb(), see the comment below, and fwiw "_after_atomic" would not
>> work.
> 
> For this one, I think all we need to do is have the wq_list_empty()
> check be fully stable. If we read:
> 
> nr_wait = atomic_read(&ctx->cq_wait_nr);
> 
> right before a waiter does:
> 
> atomic_set(&ctx->cq_wait_nr, foo);
> set_current_state(TASK_INTERRUPTIBLE);
> 
> then we need to ensure that the "I have work" check in
> io_cqring_wait_schedule() sees the work. The spin_unlock() has release
> semantics, and the current READ_ONCE() for work check sbould be enough,
> no?

To answer my own question - no, it's not enough. Let me think about this
a bit.

-- 
Jens Axboe