Re: [PATCH 1/1] Revert "RDMA/rxe: Add workqueue support for rxe tasks"

[Leon Romanovsky <leon@kernel.org>]

On Wed, Sep 27, 2023 at 11:51:12AM -0500, Bob Pearson wrote:
> On 9/26/23 15:24, Bart Van Assche wrote:
> > On 9/26/23 11:34, Bob Pearson wrote:
> >> I am working to try to reproduce the KASAN warning. Unfortunately,
> >> so far I am not able to see it in Ubuntu + Linus' kernel (as you described) on metal. The config file is different but copies the CONFIG_KASAN_xxx exactly as yours. With KASAN enabled it hangs on every iteration of srp/002 but without a KASAN warning. I am now building an openSuSE VM for qemu and will see if that causes the warning.
> > 
> > Hi Bob,
> > 
> > Did you try to understand the report that I shared? My conclusion from
> > the report is that when using tasklets rxe_completer() only runs after
> > rxe_requester() has finished and also that when using work queues that
> > rxe_completer() may run concurrently with rxe_requester(). This patch
> > seems to fix all issues that I ran into with the rdma_rxe workqueue
> > patch (I have not tried to verify the performance implications of this
> > patch):
> > 
> > diff --git a/drivers/infiniband/sw/rxe/rxe_task.c b/drivers/infiniband/sw/rxe/rxe_task.c
> > index 1501120d4f52..6cd5d5a7a316 100644
> > --- a/drivers/infiniband/sw/rxe/rxe_task.c
> > +++ b/drivers/infiniband/sw/rxe/rxe_task.c
> > @@ -10,7 +10,7 @@ static struct workqueue_struct *rxe_wq;
> > 
> >  int rxe_alloc_wq(void)
> >  {
> > -       rxe_wq = alloc_workqueue("rxe_wq", WQ_UNBOUND, WQ_MAX_ACTIVE);
> > +       rxe_wq = alloc_workqueue("rxe_wq", WQ_UNBOUND, 1);
> >         if (!rxe_wq)
> >                 return -ENOMEM;
> > 
> > Thanks,
> > 
> > Bart.

<...>

> Nevertheless this is a good hint since it seems to imply that there is a race between the requester and
> completer which is certainly possible.

Bob, Bart

Can you please send this change as a formal patch?
As we prefer workqueue with bad performance implementation over tasklets.

Thanks

> 
> Bob
> 
>