linux-kernel - Re: [PATCH 10/14] scsi: only maintain target_blocked if the driver has a target queue limit

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Message-ID: <20140709150548.GB25257@lst.de>
Date:	Wed, 9 Jul 2014 17:05:48 +0200
From:	Christoph Hellwig <hch@....de>
To:	Hannes Reinecke <hare@...e.de>
Cc:	Christoph Hellwig <hch@....de>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jens Axboe <axboe@...nel.dk>,
	Bart Van Assche <bvanassche@...ionio.com>,
	Robert Elliott <Elliott@...com>, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/14] scsi: only maintain target_blocked if the driver
	has a target queue limit

On Wed, Jul 09, 2014 at 01:19:41PM +0200, Hannes Reinecke wrote:
>>    host_not_ready:
>> -	atomic_dec(&scsi_target(sdev)->target_busy);
>> +	if (scsi_target(sdev)->can_queue > 0)
>> +		atomic_dec(&scsi_target(sdev)->target_busy);
>>    not_ready:
>>   	/*
>>   	 * lock q, handle tag, requeue req, and decrement device_busy. We
>>
> Hmm. 'can_queue' can be changed by the LLDD. Don't we need some sort of 
> synchronization here?

While a few drivers change the host can_queue value at runtime none
do for the target.  While I don't think driver should even change the
host one even modification to the target one is perfectly fine as long
as no driver drops it to zero.

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