[Lucid] SRU: Allow mmc cards to be used with unsafe resume

[Stefan Bader]

Stefan Bader wrote:
> Leann Ogasawara wrote:
>> On Sat, 2010-04-03 at 11:50 +0200, Stefan Bader wrote:
>>> SRU Justification:
>>>
>>> Impact: On suspend, mmc cards are ejected on suspend and rediscovered at
>>> resume. There seems to be a bug in that in Lucid as a mounted mmc card
>>> causes the suspend to hang. Also ejecting and rediscovering is actually
>>> annoying if the card contains extensions to the home directory or a root
>>> filesystem.
>>>
>>> Fix: This is not a real fix, but a workaround. In the Lucid code there is
>>> a compile time only option to allow the mmc/sd card to be mounted and just
>>> get reused on resume. Contrary to the unsafe title there arctually is some
>>> safeguarding code to check the cards id before blindly using it.
>>> The following patch leaves the default as it is now, but allows users to
>>> change the mode with a boot parameter or by writing into the modules parameter
>>> in sysfs.
>>>
>>> Testcase: Suspend with mounted SD card hangs on its way down. With removable=0
>>> it will go down and come up without apparent problems.
>>>
>>>
>>> From faf4b61efc07ba61195e97b42200331aea030b0d Mon Sep 17 00:00:00 2001
>>> From: Ben Hutchings <ben at decadent.org.uk>
>>> Date: Mon, 14 Dec 2009 18:01:29 -0800
>>> Subject: [PATCH] mmc: add module parameter to set whether cards are assumed removable
>>>
>>> Some people run general-purpose distribution kernels on netbooks with
>>> a card that is physically non-removable or logically non-removable
>>> (e.g. used for /home) and cannot be cleanly unmounted during suspend.
>>> Add a module parameter to set whether cards are assumed removable or
>>> non-removable, with the default set by CONFIG_MMC_UNSAFE_RESUME.
>>>
>>> In general, it is not possible to tell whether a card present in an MMC
>>> slot after resume is the same that was there before suspend.  So there are
>>> two possible behaviours, each of which will cause data loss in some cases:
>>>
>>> CONFIG_MMC_UNSAFE_RESUME=n (default): Cards are assumed to be removed
>>> during suspend.  Any filesystem on them must be unmounted before suspend;
>>> otherwise, buffered writes will be lost.
>>>
>>> CONFIG_MMC_UNSAFE_RESUME=y: Cards are assumed to remain present during
>>> suspend.  They must not be swapped during suspend; otherwise, buffered
>>> writes will be flushed to the wrong card.
>>>
>>> Currently the choice is made at compile time and this allows that to be
>>> overridden at module load time.
>>>
>>> BugLink: http://bugs.launchpad.net/bugs/477106
>>>
>>> Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
>>> Cc: Wouter van Heyst <larstiq at larstiq.dyndns.org>
>>> Cc: <linux-mmc at vger.kernel.org>
>>> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
>>> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
>>> (cherry-picked from commit bd68e0838fe85794b06892054772fa013a8d1986 upstream)
>>> Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
>> Looks ok to me.  Stefan, will you be building test kernels for bug
>> 477106?
>>
> Ah, actually I have but only (selfishly) for myself and only for i386. But I
> will let it build on ronne and shove over the kernels tomorrow.
> [As my Aspire One exactly shows that hang I can at least confirm it seems to
> work for me :)]
> 
> Stefan
> 
Ok, its there now and the report has been updated.

Stefan