RE: [PATCH 6/8] Drivers: scsi: storvsc: Implement an abort handler

KY Srinivasan
2014-07-12T16:35:10Z

> -----Original Message-----
> From: Richard Weinberger [mailto:richard.weinberger@gmail.com]
> Sent: Saturday, July 12, 2014 9:17 AM
> To: KY Srinivasan
> Cc: Christoph Hellwig; linux-kernel@vger.kernel.org;
> devel@linuxdriverproject.org; ohering@suse.com;
> jbottomley@parallels.com; jasowang@redhat.com; apw@canonical.com;
> linux-scsi@vger.kernel.org
> Subject: Re: [PATCH 6/8] Drivers: scsi: storvsc: Implement an abort handler
>
> On Thu, Jul 10, 2014 at 12:33 PM, Richard Weinberger
> <richard.weinberger@gmail.com> wrote:
> > On Wed, Jul 9, 2014 at 8:51 PM, KY Srinivasan <kys@microsoft.com> wrote:
> >>
> >>
> >>> -----Original Message-----
> >>> From: Christoph Hellwig [mailto:hch@infradead.org]
> >>> Sent: Wednesday, July 9, 2014 1:44 AM
> >>> To: KY Srinivasan
> >>> Cc: linux-kernel@vger.kernel.org; devel@linuxdriverproject.org;
> >>> ohering@suse.com; jbottomley@parallels.com; jasowang@redhat.com;
> >>> apw@canonical.com; linux-scsi@vger.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?
>
> ping?

Sorry for the delayed response. Yes we have seen resets and potentially the file system mounted
Read-only because of the I/O timeouts. We have increased the standard scsi timeouts. Implementing the
Timedout handler as we have done now should solve this problem.

K. Y
>
> --
> Thanks,
> //richard