Re: Regression in io_uring, leading to data corruption

[Timothy Pearson <tpearson@raptorengineering.com>]

----- Original Message -----
> From: "Jens Axboe" <axboe@kernel.dk>
> To: "Timothy Pearson" <tpearson@raptorengineering.com>
> Cc: "regressions" <regressions@lists.linux.dev>, "Pavel Begunkov" <asml.silence@gmail.com>
> Sent: Thursday, November 9, 2023 11:38:10 AM
> Subject: Re: Regression in io_uring, leading to data corruption

> On 11/9/23 10:36 AM, Timothy Pearson wrote:
>>> Hmm ok, that is odd. How quickly does it trigger for you?
>> 
>> Almost immediately.  Third pass in this case, which is pretty typical
>> -- without any delays etc. it will normally fail in under 10
>> iterations.  When I add other delays in e.g. the worker thread it
>> becomes less likely to fail, but still fails.   Only adding the udelay
>> in the one specific (IRQ locked) location allows it to pass all 200
>> iterations.
> 
> What specific IRQ locked location? Hard to know where you are adding
> these things without seeing the patches.
> 
> --
> Jens Axboe

Sorry about that.  Here's the patch that automagically makes things work (bear in mind line numbers etc. are munged since I have a bunch of other debug stuff in here at this point):

 static void io_wqe_dec_running(struct io_worker *worker)
@@ -312,19 +326,39 @@ static void io_wqe_dec_running(struct io_worker *worker)
        if (!(worker->flags & IO_WORKER_F_UP))
                return;

+       udelay(1000);
        if (atomic_dec_and_test(&acct->nr_running) && io_wqe_run_queue(wqe)) {
                atomic_inc(&acct->nr_running);
                atomic_inc(&wqe->wq->worker_refs);