Subject: Re: [PATCH 2/9] IB: add a proper completion queue abstraction
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
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CC: Christoph Hellwig <hch@lst.de>,
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From: Bart Van Assche <bart.vanassche@sandisk.com>
Message-ID: <56539421.9050705@sandisk.com>
Date: Mon, 23 Nov 2015 14:33:05 -0800
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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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