Re: [PATCH] RDMA/rxe: Fix a race condition related to the QP error state

[Bart Van Assche <Bart.VanAssche@wdc.com>]

On Thu, 2018-01-11 at 21:00 +0200, Leon Romanovsky wrote:
> On Thu, Jan 11, 2018 at 04:02:33PM +0000, Bart Van Assche wrote:
> > On Thu, 2018-01-11 at 08:22 +0200, Leon Romanovsky wrote:
> > > The proposed patch definitely decreases the chance of races, but it is not fixing them.
> > > There is a chance to have change in qp state immediately after your "if ..." check.
> > 
> > Hello Leon,
> > 
> > Please have a look at rxe_qp_error() and you will see that the patch I posted
> > is a proper fix. In the scenario you described rxe_qp_error() will trigger a
> > run of rxe_completer().
> 
> Bart,
> 
> What am I missing?
> 
> CPU1							CPU2
> 							if (unlikely....
> 						<---
> /* move the qp to the error state */
> void rxe_qp_error(struct rxe_qp *qp)
> {
>         qp->req.state = QP_STATE_ERROR;
>         qp->resp.state = QP_STATE_ERROR;
>         qp->attr.qp_state = IB_QPS_ERR;
> 						--->
> 							rxe_run_task(&qp->req.task, must_sched);
> 
> 
> 
> It is more or less the same as without "if (unlikely..."

Hello Leon,

In the above the part of rxe_qp_error() that I was referring to in my e-mail
is missing:

	if (qp_type(qp) == IB_QPT_RC)
		rxe_run_task(&qp->comp.task, 1);

Bart.