Re: [dm-devel] block_abort_queue (blk_abort_request) racing with scsi_request_fn

[Mike Anderson <andmike@linux.vnet.ibm.com>]

Mike Snitzer <snitzer@redhat.com> wrote:
> Hi Mike,
> 
> On Fri, Nov 12 2010 at 12:54pm -0500,
> Mike Anderson <andmike@linux.vnet.ibm.com> wrote:
> 
> > By not directly timing out the I/O but accelerating the timeout by a
> > factor. The value could be calculated as a percentage of the queue timeout
> > value for a default with the option of exposing a sysfs attribute
> > similar to fast_io_fail_tmo. The attribute could also provide a off
> > method which we do not have today and is my bad that we do not have one
> > (I posted the features patch to multipath but did not followup which
> > would have provided a off).
> 
> You're referring to these patches:
> https://patchwork.kernel.org/patch/96674/
> https://patchwork.kernel.org/patch/96673/
> 

Yes these are the patches that I was referring to.

> Do you have an interest in pursuing these further? 

Yes.

> In the near-term
> should we default to off (so introduce MP_FEATURE_ABORT_Q) -- given the
> current race which exposes corruption?
> 

Given the current race exposure default to off might be the best choice.

> Or are you now interested in accelerating the timeout?  I'd need to
> review this thread in more detail to give you an opinion.  But I do know
> that simply disabling dm-mpath's call to blk_abort_queue() enables some
> extensive path failure load testing to _not_ cause the list corruption
> that leads to a crash.

I think the on/off control plus a fix to address the issue when it is on
would be good. Since I do not believe we want the impact the normal IO
path by more lock bouncing adding modification of the blk_abort_queue
function appeared like one of the least distributive options. There might
be others.

-andmike
--
Michael Anderson
andmike@linux.vnet.ibm.com