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

Leon Romanovsky
2018-01-12T06:23:59Z

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On Thu, Jan 11, 2018 at 07:07:06PM +0000, Bart Van Assche wrote:
> 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);

But it is exactly where race exists, as long QP isn't protected, it can
switch CPUs and create race.

Thanks

>
> Bart.

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