linux-kernel - Re: [PATCH 6/8] Drivers: scsi: storvsc: Implement an abort handler

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Message-ID: <CAFLxGvzFTeE9J-4KFUn9q1fggB_pGBHEMEPcBtDhje+uRm7yMw@mail.gmail.com>
Date:	Thu, 10 Jul 2014 12:33:05 +0200
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"ohering@...e.com" <ohering@...e.com>,
	"jbottomley@...allels.com" <jbottomley@...allels.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"apw@...onical.com" <apw@...onical.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH 6/8] Drivers: scsi: storvsc: Implement an abort handler

On Wed, Jul 9, 2014 at 8:51 PM, KY Srinivasan <kys@...rosoft.com> wrote:
>
>
>> -----Original Message-----
>> From: Christoph Hellwig [mailto:hch@...radead.org]
>> Sent: Wednesday, July 9, 2014 1:44 AM
>> To: KY Srinivasan
>> Cc: linux-kernel@...r.kernel.org; devel@...uxdriverproject.org;
>> ohering@...e.com; jbottomley@...allels.com; jasowang@...hat.com;
>> apw@...onical.com; linux-scsi@...r.kernel.org
>> Subject: Re: [PATCH 6/8] Drivers: scsi: storvsc: Implement an abort handler
>>
>> On Tue, Jul 08, 2014 at 05:46:50PM -0700, K. Y. Srinivasan wrote:
>> > Implement a simple abort handler. The host does not support "Abort";
>> > just ensure that all inflight I/Os have been accounted for.
>>
>> The abort handler should abort a single command, not wait for all of them.
>> What issue do you see that this tries to address?
>
> On Azure, we sometimes have unbounded I/O latencies and some distributions (such as SLES12) based on recent kernels are invoking
> the "Abort Handler". Unfortunately, our scsi emulation on the host does not support aborting a command.
> The issue I have seen is that the upper level scsi code attempts error recovery when the command times out and finally frees up the command.
> The host subsequently responds to the command that has timed out and since the memory has been freed up, we end up touching freed memory
> in this driver. Since the host is also doing error recovery, by just delaying the error handler in the guest until we can account for all the in-flight commands,
> we can get around the problem.

I see strange issues in Azure and maybe they are related to this.
Some Linux machines crash in a way that no disk IO is possible (thus,
no SSH for me) but they still respond to
ping. It happens rather seldom (every few weeks).

Do you see similar symptoms?

-- 
Thanks,
//richard
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