linux-kernel - Re: [PATCH] MMC: core: cap MMC card timeouts at 2 seconds.

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Message-ID: <CAPDyKFrtdFn-t43r03m630gScYz6Cz+asfruSa=sGcxP0+C+tQ@mail.gmail.com>
Date:	Thu, 31 May 2012 23:00:31 +0800
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	"Torne (Richard Coles)" <torne@...gle.com>
Cc:	cjb@...top.org, linus.walleij@...aro.org, jh80.chung@...sung.com,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	ben@...adent.org.uk
Subject: Re: [PATCH] MMC: core: cap MMC card timeouts at 2 seconds.

Hi Richard,

On 31 May 2012 18:15, Torne (Richard Coles) <torne@...gle.com> wrote:
> On 31 May 2012 11:00, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> Hi Richard,
>>
>> On 29 May 2012 17:02, Torne (Richard Coles) <torne@...gle.com> wrote:
>>> From: "Torne (Richard Coles)" <torne@...gle.com>
>>>
>>> MMC CSD info can specify very large, ridiculous timeouts, big enough to
>>> overflow timeout_ns on 32-bit machines. This can result in the card
>>> timing out on every operation because the wrapped timeout value is far
>>> too small.
>>>
>>> Fix the overflow by capping the result at 2 seconds.  Cards specifying
>>> longer timeouts are almost certainly insane, and host controllers
>>> generally cannot support timeouts that long in any case.
>>>
>>> 2 seconds should be plenty of time for any card to actually function;
>>> the timeout calculation code is already using 1 second as a "worst case"
>>> timeout for cards running in SPI mode.
>>>
>>> Signed-off-by: Torne (Richard Coles) <torne@...gle.com>
>>> ---
>>>  drivers/mmc/core/core.c |   11 ++++++++++-
>>>  1 files changed, 10 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>>> index 0b6141d..3b4a9fc 100644
>>> --- a/drivers/mmc/core/core.c
>>> +++ b/drivers/mmc/core/core.c
>>> @@ -512,7 +512,16 @@ void mmc_set_data_timeout(struct mmc_data *data, const struct mmc_card *card)
>>>        if (data->flags & MMC_DATA_WRITE)
>>>                mult <<= card->csd.r2w_factor;
>>>
>>> -       data->timeout_ns = card->csd.tacc_ns * mult;
>>> +       /*
>>> +        * The timeout in nanoseconds may overflow with some cards. Cap it at
>>> +        * two seconds both to avoid the overflow and also because host
>>> +        * controllers cannot generally generate timeouts that long anyway.
>>> +        */
>>> +       if (card->csd.tacc_ns <= (2 * NSEC_PER_SEC) / mult)
>>> +               data->timeout_ns = card->csd.tacc_ns * mult;
>>> +       else
>>> +               data->timeout_ns = 2 * NSEC_PER_SEC;
>>> +
>>
>> The above looks OK to me, although if doing this for tacc_ns we might
>> want to do this for tacc_clks as well. Could we include that is this
>> patch as well?
>
> timeout_clks can't overflow, that I can see: the highest possible
> value for tacc_clks is 25500 (it's an 8 bit field specified in
> 100-clock increments) and the highest mult is 12800 (r2w_factor only
> goes up to 128). This only makes 0x13747800 :)
>

Thanks for sorting this out and sorry for me being too lazy to read
the spec. :-)

Acked-by: Ulf Hansson <ulf.hansson@...aro.org>

Kind regards
Ulf Hansson
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