On 01/06/12 13:20, Torne (Richard Coles) wrote: > On 1 June 2012 11:09, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >> On 01/06/12 12:32, Torne (Richard Coles) wrote: >>> On 1 June 2012 10:31, Torne (Richard Coles) <torne@xxxxxxxxxx> wrote: >>>> On 1 June 2012 09:35, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >>>>> On 29/05/12 05:32, Ben Hutchings wrote: >>>>>> On Mon, 2012-05-28 at 18:31 +0100, Torne (Richard Coles) wrote: >>>>>>> From: "Torne (Richard Coles)" <torne@xxxxxxxxxx> >>>>>>> >>>>>>> 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. >>>>>> >>>>>> Needs a 'Signed-off-by'. >>>>>> >>>>>>> --- >>>>>>> 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; >>>>>> >>>>>> We clearly need to guard against overflow here, and this is the correct >>>>>> way to clamp the multiplication. I can't speak as to whether 2 seconds >>>>>> is the right limit. >>>>> >>>>> The host controllers I have looked at have a limit of around 2.5 seconds. >>>>> >>>>> But why not just use the size of the type as the limit? e.g. >>>>> >>>>> if (card->csd.tacc_ns <= UINT_MAX / mult) >>>>> data->timeout_ns = card->csd.tacc_ns * mult; >>>>> else >>>>> data->timeout_ns = UINT_MAX; >>>> >>>> The host controller drivers don't seem to all do a very good job of >>>> preventing further overflows or handling large values correctly >>>> (though some do). sdhci takes the especially annoying additional step >>>> of printk'ing a warning for *every single MMC command* where >>>> data->timeout_ns is larger than the controller can accommodate. >>>> Capping it to a value with a sensible order of magnitude seems to make >>>> it more likely that cards with obviously bogus CSD parameters will >>>> actually work. I don't object to using a larger number for the limit, >>>> but UINT_MAX on a 64-bit system obviously doesn't limit this at all >>>> and will leave you with timeouts up to 17 minutes, which seems >>>> ridiculous :) >>> >>> Er, not 17 minutes; 102.4 seconds as I used later in my mail. SD cards >>> have their timeouts capped already, so their larger 100x multiplier is >>> not a problem; 102.4 seconds is the longest for an MMC card. >>> >> >> Linux is LP64. i.e. "int" is always 32-bit in the kernel > > Oh, sorry; didn't think that through. So, yeah, that'd be 4.29 > seconds, which is still too long for many hosts :) > >>>> My original motivation for this patch is that I have a device with an >>>> eMMC that specifies a 25.5 second timeout, attached to a sdhci host >>>> whose maximum timeout is 2.8 seconds. Originally I proposed a patch to >>>> just remove the warning in sdhci, but nobody replied, and when I >>>> realised there was actually an overflow happening I opted to fix that >>>> instead. >>>> >>>> So, yeah, we could use UINT_MAX, but then at minimum I also need to >>>> kill the warning in sdhci to make my device work, and probably all the >>>> host controller drivers need to be checked to make sure they don't use >>>> timeout_ns in a way that can overflow. >>>> >>>> I've also just noticed that struct mmc_data's comment for timeout_ns >>>> says /* data timeout (in ns, max 80ms) */ which is not true (the max >>>> is 102.4 seconds if my math is correct), which may have contributed to >>>> the host drivers not being too careful :) >>>> >>>> What do you think? >> >> If you can identify the card, the you could make a new quirk in a fashion >> similar to mmc_card_long_read_time(). >> >> Alternatively you could make use of SDHCI_QUIRK_BROKEN_TIMEOUT_VAL or >> introduce your own sdhci quirk to suppress the warning. > > Those would work, but it seems silly to me to suppress the warning > only for some cards, or to cap the timeout only for some cards. The > best way to identify a card that has a "broken" timeout value is.. if > the timeout value is a really big number, no? I am very skeptical that > there is a card out there anywhere that will actually take more than > two seconds (or 4.29 seconds, if you prefer) to successfully complete > a command. > > The warning itself seems to have extremely limited use; there's > nothing you can do about it other than suppress it (the driver is > already capping the timeout for you), and because timeouts are > calculated per-command the warning is absurdly noisy (in fact, the fun > part on my system was the warning being logged to klogd, being written > to logfiles on the eMMC, causing more warnings, causing more log > messages, etc) :) sdhci is the only host driver that complains about > this; it seems logical for the warning to apply to all hosts, or to > none of them... I just noticed that from linux 3.4, the SD write timeout is now 3 seconds triggering the sdhci driver warning on every write on every SD card. So change pr_warning to DGB in sdhci_calc_timeout(). Chris? -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
