linux-kernel - Re: 4.13 on thinkpad x220: oops when writing to SD card

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Date:   Fri, 8 Sep 2017 10:51:49 +0800
From:   Shawn Lin <shawn.lin@...k-chips.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     shawn.lin@...k-chips.com, Adrian Hunter <adrian.hunter@...el.com>,
        Pavel Machek <pavel@....cz>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Seraphime Kirkovski <kirkseraph@...il.com>
Subject: Re: 4.13 on thinkpad x220: oops when writing to SD card

On 2017/9/8 4:02, Linus Walleij wrote:
> On Thu, Sep 7, 2017 at 9:18 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> 
>> Even if this fixes the problem it seems like we are papering over the
>> real issue, which earlier fixes also did during the release cycle for
>> v4.13.
> 
> I think this is the real solution to the issue.
> 
>>> Another unrelated issue with mmc_init_request() is that mmc_exit_request()
>>> is not called if mmc_init_request() fails, which means mmc_init_request()
>>> must free anything it allocates when it fails.
>>
>> Yes, the situations it's just too fragile. We need to fix the behavior
>> properly, although I haven't myself been able to investigate exactly
>> how yet.
>>
>> Adding, Linus, perhaps he has some ideas.
> 
> Maybe we should simply bite the bullet and do what was suggested
> by another contributor when I refactored the bounce buffer handling:
> simply delete the bounce buffer code and let any remaining (few?)
> legacy devices suffer a bit (performancewise) at the gain of way
> simpler code?

Are you in the same page with what Adrian pointed to?

IIUC, the issue is:
init_rq_fn will be called each time when trying to create new reuqest
from the pre-allocated request_list memeory pool, and exit_rq_fn will is
in the corresponding routine to free request from request_list
(blk_free_request) when finished. But if alloc_request_size fails, it
won't call exit_rq_fn, so you need to prevent memory leak on your own
error path of init_rq_fn.

But you seem to talk about removing the bounce buffer and so finally
get rid of registering init_rq_fn/exit_rq_fn? That is another thing,
and what we right now need to do is to fix the pontential memory leak.
It's quite a simple action, right? :)

> 
> I am a bit hesitant about that because Pierre Ossman said it was
> actually a big win on the SDHC hosts that made use of it at one
> point.

You had removed packed cmd support to simplify the code, so I think
this is another trade-off need to ask: What you want? and keep
consistent with the direction you insisted on.

> 
> Yours,
> Linus Walleij
> 
> 
>