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

[Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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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..."

Thanks

>
> Bart.

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