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Re: [dm-devel] [PATCH 4/7] dm mpath: remove process_queued_ios()



On 02/10/2014 02:30 PM, Mike Snitzer wrote:
> On Tue, Feb 04 2014 at  6:31am -0500,
> Hannes Reinecke <hare suse de> wrote:
> 
>> On 02/04/2014 12:26 PM, Junichi Nomura wrote:
>>> On 02/04/14 19:54, Hannes Reinecke wrote:
>>>> We only need to take care to add a small delay when calling
>>>> __pg_init_all_paths() to move processing off to a workqueue; otherwise
>>>> pg_init_done() might end up calling scsi_dh_activate() directly, which
>>>> might use non-atomic memory allocations or issue I/O.
>>>
>>> Hi Hannes,
>>>
>>> could you tell me how "might end up calling scsi_dh_active()" happens?
>>>
>>>   queue_delayed_work()
>>>     queue_delayed_work_on()
>>>       __queue_delayed_work()
>>>         if (!delay)
>>>           __queue_work()
>>>             get_work_pool()
>>>             insert_work()
>>>               set_work_pwq()
>>>               get_pwq()
>>>               if (__need_more_worker())
>>>                 wake_up_worker()
>>>
>>> queue_work() doesn't execute the work itself.
>>>
>>> What am I missing?
>>>
>> As mentioned, I stumbled across the same issue when developing the
>> asynchronous SCSI aborts. I'll see to have it recreated with this
>> patchset.
> 
> Just to verify, this seems to be the only outstanding question for this
> patchset?
> 
> What value are you using for HZ?  If this portion of the change does
> turn out to be meaningul: Rather than tieing to HZ should we just use an
> explicitly non-zero value for __pg_init_all_paths()'s @min_delay?
> 
The actual amount here is irrelevant, as long as it's non-zero.
It's just there to force execution of the work item off the current
thread.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare suse de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)


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