linux-kernel - Re: Upstream kernel fails to run on qemu-sparc64 due to commit 889fa31f0 (blk-mq: reduce unnecessary software queue looping)

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Date:	Fri, 17 Apr 2015 08:26:11 -0600
From:	Jens Axboe <axboe@...com>
To:	Guenter Roeck <linux@...ck-us.net>, <linux-kernel@...r.kernel.org>
CC:	Chong Yuan <chong.yuan@...blaze.com>,
	Wenbo Wang <wenbo.wang@...blaze.com>
Subject: Re: Upstream kernel fails to run on qemu-sparc64 due to commit 889fa31f0
 (blk-mq: reduce unnecessary software queue looping)

On 04/17/2015 07:32 AM, Guenter Roeck wrote:
> On Thu, Apr 16, 2015 at 11:32:20PM -0700, Guenter Roeck wrote:
>> Hi,
>>
>> my qemu-sparc64 tests fail to run with kernel v4.0-7245-ga39ef1a7c609.
>> Bisect points to commit 889fa31f00b ("blk-mq: reduce unnecessary software
>> queue looping"). Reverting this commit fixes the problem.
>>
>> I had a look into the commit, but I have no idea what might be wrong.
>>
>> I made the bisect log, images, configuration file, root file system, and directions
>> on how to run the images available at https://urldefense.proofpoint.com/v1/url?u=http://server.roeck-us.net/qemu/sparc64&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=3JMVyziIyZtZ5cv9eWNLwQ%3D%3D%0A&m=%2FUVX9MC8j8RmqOwlL6HnyBe%2FFSO5xSJdG3GTTzADFYk%3D%0A&s=caaf39bb4246d5223f9dea93771fdb075f9046b6fdf1822b7da21d7665da71d5.
>>
>> Please let me know if there is any other information I can provide.
>>
> As additional information:
>
> +                * Set the map size to the number of mapped software queues.
> +                * This is more accurate and more efficient than looping
> +                * over all possibly mapped software queues.
> +                */
> +               map->map_size = hctx->nr_ctx / map->bits_per_word;
>
> On my system, hctx->nr_ctx is 1, and map->bits_per_word is 8.
> Thus map->map_size is set to 0, which doesn't make much sense.


> The system comes up if I replace the above code with
> 		map->map_size = DIV_ROUND_UP(hctx->nr_ctx, map->bits_per_word);
>
> I have no idea if that is the correct fix, though.

Ugh, yes indeed, looks like the <= was lost from a previous patch. Now I 
wonder why it I didn't see any hangs with this... Thanks for reporting, 
I'll get a fix in today.

-- 
Jens Axboe

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