linux-kernel - Re: [PATCH 09/14] scsi: fix the {host,target,device}

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Message-ID: <yq1silpgssh.fsf@sermon.lab.mkp.net>
Date:	Fri, 25 Jul 2014 15:08:46 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Christoph Hellwig <hch@....de>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Bart Van Assche <bvanassche@...ionio.com>,
	Mike Christie <michaelc@...wisc.edu>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Robert Elliott <Elliott@...com>, Webb Scales <webbnh@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/14] scsi: fix the {host,target,device}_blocked counter mess

>>>>> "Christoph" == Christoph Hellwig <hch@....de> writes:

Christoph> Seems like these counters are missing any sort of
Christoph> synchronization for updates, as a over 10 year old comment
Christoph> from me noted.  Fix this by using atomic counters, and while
Christoph> we're at it also make sure they are in the same cacheline as
Christoph> the _busy counters and not needlessly stored to in every I/O
Christoph> completion.

Christoph> With the new model the _busy counters can temporarily go
Christoph> negative, so all the readers are updated to check for > 0
Christoph> values.  Longer term every successful I/O completion will
Christoph> reset the counters to zero, so the temporarily negative
Christoph> values will not cause any harm.

Reviewed-by: Martin K. Petersen <martin.petersen@...cle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering
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