Re: 4.14-rc2 on thinkpad x220: out of memory when inserting mmc card

[Ulf Hansson <ulf.hansson@linaro.org>]

On 4 October 2017 at 09:53, Linus Walleij <linus.walleij@linaro.org> wrote:
> On Tue, Oct 3, 2017 at 8:30 AM, Adrian Hunter <adrian.hunter@intel.com> wrote:
>> On 02/10/17 17:09, Linus Walleij wrote:
>>> On Sun, Oct 1, 2017 at 12:57 PM, Tetsuo Handa
>>> <penguin-kernel@i-love.sakura.ne.jp> wrote:
>>>
>>>>>> I inserted u-SD card, only to realize that it is not detected as it
>>>>>> should be. And dmesg indeed reveals:
>>>>>
>>>>> Tetsuo asked me to report this to linux-mm.
>>>>>
>>>>> But 2^4 is 16 pages, IIRC that can't be expected to work reliably, and
>>>>> thus this sounds like MMC bug, not mm bug.
>>>
>>>
>>> I'm not sure I fully understand this error message:
>>> "worker/2:1: page allocation failure: order:4"
>>>
>>> What I guess from context is that the mmc_init_request()
>>> call is failing to allocate 16 pages, meaning for 4K pages
>>> 64KB which is the typical bounce buffer.
>>>
>>> This is what the code has always allocated as bounce buffer,
>>> but it used to happen upfront, when probing the MMC block layer,
>>> rather than when allocating the requests.
>>
>> That is not exactly right.  As I already wrote, the memory allocation used
>> to be optional but became mandatory with:
>>
>>   commit 304419d8a7e9204c5d19b704467b814df8c8f5b1
>>   Author: Linus Walleij <linus.walleij@linaro.org>
>>   Date:   Thu May 18 11:29:32 2017 +0200
>>
>>       mmc: core: Allocate per-request data using the block layer core
>
> Yes you are right, it used to look like this, with the bounce buffer
> hiding behind a Kconfig symbol:
>
> #ifdef CONFIG_MMC_BLOCK_BOUNCE
>     if (host->max_segs == 1) {
>         unsigned int bouncesz;
>
>         bouncesz = MMC_QUEUE_BOUNCESZ;
>
>         if (bouncesz > host->max_req_size)
>             bouncesz = host->max_req_size;
>         if (bouncesz > host->max_seg_size)
>             bouncesz = host->max_seg_size;
>         if (bouncesz > (host->max_blk_count * 512))
>             bouncesz = host->max_blk_count * 512;
>
>         if (bouncesz > 512 &&
>             mmc_queue_alloc_bounce_bufs(mq, bouncesz)) {
>             blk_queue_bounce_limit(mq->queue, BLK_BOUNCE_ANY);
>             blk_queue_max_hw_sectors(mq->queue, bouncesz / 512);
>             blk_queue_max_segments(mq->queue, bouncesz / 512);
>             blk_queue_max_segment_size(mq->queue, bouncesz);
>
>             ret = mmc_queue_alloc_bounce_sgs(mq, bouncesz);
>             if (ret)
>                 goto cleanup_queue;
>             bounce = true;
>         }
>     }
> #endif
>
> I recently concluded that I find no evidence whatsoever that anyone
> turned this symbol on. Actually. (Checked defconfigs and distro configs.)
> The option was just sitting there unused.
> This code was never exercised except by some people who turned it
> on on their custom kernels in the past. It's in practice dead code.
>
> My patch started to allocate and use bounce buffers for all hosts
> with max_segs == 1, unless specifically flagged NOT to use bounce
> buffers.
>
> That wasn't smart, I should have just deleted them. Mea culpa.
>
> So that is why I asked Ulf to simply put the patch deleting the bounce
> buffers that noone is using to fixes, and it should fix this problem.

Adrian, Linus,

Thanks for looking into the problem! I am queuing up the patch
deleting bounce buffers for fixes asap!

Kind regards
Uffe