netdev - Re: [PATCH] SIW: User interface

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Date:	Tue, 05 Oct 2010 09:17:34 -0500
From:	Steve Wise <swise@...ngridcomputing.com>
To:	Bernard Metzler <bmt@...ich.ibm.com>
CC:	netdev@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH] SIW: User interface

On 10/05/2010 01:54 AM, Bernard Metzler wrote:


<snip>

> +
> +/*
> + * siw_post_send()
> + *
> + * Post a list of S-WR's to a SQ.
> + *
> + * @ofa_qp:	OFA QP contained in siw QP
> + * @wr:		Null terminated list of user WR's
> + * @bad_wr:	Points to failing WR in case of synchronous failure.
> + */
> +int siw_post_send(struct ib_qp *ofa_qp, struct ib_send_wr *wr,
> +		  struct ib_send_wr **bad_wr)
> +{
> +	struct siw_wqe	*wqe = NULL;
> +	struct siw_qp	*qp = siw_qp_ofa2siw(ofa_qp);
> +
> +	unsigned long flags;
> +	int rv = 0;
> +
> +	dprint(DBG_WR|DBG_TX, "(QP%d): state=%d\n",
> +		QP_ID(qp), qp->attrs.state);
> +
> +	/*
> +	 * Acquire QP state lock for reading. The idea is that a
> +	 * user cannot move the QP out of RTS during TX/RX processing.
> +	 */
> +	down_read(&qp->state_lock);
> +
>    

I don't think you can use a rw_semaphore here because it potentially can 
block.  You cannot block/sleep in the post_send/post_recv (and some 
other) RDMA provider functions.  See 
Documentation/infiniband/core_locking.txt.


Steve.
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