linux-kernel - Re: [PATCH 2/9] IB: add a proper completion queue abstraction

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Date:	Mon, 23 Nov 2015 14:33:05 -0800
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
CC:	Christoph Hellwig <hch@....de>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"sagig@....mellanox.co.il" <sagig@....mellanox.co.il>,
	"axboe@...com" <axboe@...com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/9] IB: add a proper completion queue abstraction

On 11/23/2015 02:18 PM, Jason Gunthorpe wrote:
> On Mon, Nov 23, 2015 at 01:54:05PM -0800, Bart Van Assche wrote:
> What I don't see is how SRP handles things when the
> sendq fills up, ie the case where __srp_get_tx_iu() == NULL. It looks
> like the driver starts to panic and generates printks. I can't tell if
> it can survive that, but it doesn't look very good..

Hello Jason,

 From srp_cm_rep_handler():

		target->scsi_host->can_queue
			= min(ch->req_lim - SRP_TSK_MGMT_SQ_SIZE,
			      target->scsi_host->can_queue);

In other words, the SCSI core is told to ensure that the number of 
outstanding SCSI commands is one less than the number of elements in the 
ch->free_tx list. And since the SRP initiator serializes task management 
requests it is guaranteed that __srp_get_tx_iu() won't fail due to 
ch->free_tx being empty.

Bart.

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