linux-kernel - Re: [PATCH v2] Persistent grant maps for xen blk drivers

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Message-Id: <D5DA2BFE-803C-4195-808D-F8E4DDA20B17@gridcentric.ca>
Date:	Mon, 24 Sep 2012 11:21:51 -0400
From:	Andres Lagar-Cavilla <andreslc@...dcentric.ca>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	Andres Lagar-Cavilla <andreslc@...dcentric.ca>,
	Oliver Chick <oliver.chick@...rix.com>,
	xen-devel <xen-devel@...ts.xen.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Persistent grant maps for xen blk drivers

On Sep 24, 2012, at 11:06 AM, Konrad Rzeszutek Wilk wrote:

> On Mon, Sep 24, 2012 at 10:38:48AM -0400, Andres Lagar-Cavilla wrote:
>> On Sep 21, 2012, at 4:46 PM, Konrad Rzeszutek Wilk wrote:
>> 
>>> On Fri, Sep 21, 2012 at 02:56:22PM -0400, Konrad Rzeszutek Wilk wrote:
>>>>> *: With a PVHVM guest I get
>>>>> 
>>>>> [  261.927218] privcmd_fault: vma=ffff88002a31dce8 7f4edc095000-7f4edc195000, pgoff=c8, uv=00007f4edc15d000
>>>>> 
>>>>> thought if I applied your patch on top of v3.6-rc6 I didn't see the privcmd_fault but
>>>>> I did see the guest crash.
>>>> 
>>>> And that is due to c571898ffc24a1768e1b2dabeac0fc7dd4c14601 which I've reverted in my
>>>> #linux-next branch
>>> 
>>> Nevermind. Andres' patch by itself (so without yours) works just fine. There is
>>> something your patch and his aren't agreeing on.
>> 
>> Apart from interacting badly in combination, would either patch in isolation work well?
> 
> "work well" is not exactly the right phase I would use.
> 
> Your patch by itself (so on top v3.6-rc6) works great.
> On top of #linux-next (so v3.6-rc6 + lot of other patches for v3.7) works great.
> 
> Oliver's patch for blkback/blkfront on top of v3.6-rc6 falls flat on its face in the guest.
> Oliver's patch for blkback/blkfront on top of v3.6-rc6 + lot of other patches for v3.7 - your patch)
> falls flat on its face in the guest.
> 
> Oliver's patch for blkback/blkfront on top of v3.6-rc6 + lot of other patches for v3.7 + your patch)
> falls flat on its face in the backend with the privcmd_fault.
> 
> I think I need to figure on what tree does Oliver's patch work properly and
> figure out why it dies first in the guest and then find out why in the backend
> it dies with your patch.
> 
> Your patch is still on the train for v3.7
I saw. Great!

> 
>> 
>> I can think of only one hunk in my patch disagreeing with blkback stuff:
> 
> I can try it out.. but I am not going to get to it today or in the next
> few days.

It would seem from your testing matrix above the issue lies somewhere deeper within the blk* patches. I'll watch from the sidelines, please keep me in the loop.

Thanks,
Andres

> 
>> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
>> index eea81cf..f5681c8 100644
>> --- a/drivers/xen/grant-table.c
>> +++ b/drivers/xen/grant-table.c
>> @@ -836,6 +883,12 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
>> 	if (ret)
>> 		return ret;
>> 
>> +	/* Retry eagain maps */
>> +	for (i = 0; i < count; i++)
>> +		if (map_ops[i].status == GNTST_eagain)
>> +			gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref, map_ops + i,
>> +                                    &map_ops[i].status, __func__);
>> +
>> 	if (xen_feature(XENFEAT_auto_translated_physmap))
>> 		return ret;
>> 
>> How would you like to proceed?
>> Andres
>> 
>>> 

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