linux-kernel - Re: [RESEND][PATCH 09/10][SCSI]mpt2sas: Added module parameter 'unblock

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Date:	Thu, 21 Aug 2014 17:06:15 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	"Reddy\, Sreekanth" <Sreekanth.Reddy@...gotech.com>
Cc:	<jejb@...nel.org>, <JBottomley@...allels.com>,
	<linux-scsi@...r.kernel.org>, <Sathya.Prakash@...gotech.com>,
	<Nagalakshmi.Nandigama@...gotech.com>,
	<linux-kernel@...r.kernel.org>, <hch@...radead.org>,
	<martin.petersen@...cle.com>
Subject: Re: [RESEND][PATCH 09/10][SCSI]mpt2sas: Added module parameter 'unblock_io' to unblock IO's during disk addition

>>>>> "Sreekanth" == Reddy, Sreekanth <Sreekanth.Reddy@...gotech.com> writes:

Sreekanth> This is because, when driver receives DELAY_NOT_RESPONDING
Sreekanth> for a disk when it is undergoing addition in the SCSI Mid
Sreekanth> layer, the driver would block the I/O to that disk resulting
Sreekanth> in a deadlock. i.e the disk addition work couldn't be
Sreekanth> completed as it can't send any I/O to the disk as I/Os are
Sreekanth> blocked. Any device removal (TARGET_NOT_RESPONDING) or link
Sreekanth> update(RC_PHY_CHANGED) couldn't be processed as they are in
Sreekanth> the queue to get processed after disk addition.

Sreekanth> An module parameter 'unblock_io' is introduced which needs to
Sreekanth> be set to have this functionality enabled. By default this
Sreekanth> functionality is disabled.

This really sounds like a scenario you should be able to handle in
general (without special "don't-be-broken" module parameters).

Also, shouldn't your internal task management be able to deal with this?
Why does the sdev's state during probe affect your ability to make
forward progress?

-- 
Martin K. Petersen	Oracle Linux Engineering
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