Re: [linux-pm] Is it supposed to be ok to call del_gendisk while userspace is frozen?

[Matt Reimer]

 On Wed, May 12, 2010 at 7:50 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 11 May 2010, Matt Reimer wrote:
>
>> >> or has a consensus about how to fix this been
>> >> achieved? I'm hitting the same problem and have some time to work on a
>> >> fix.
>> >
>> > Generally, it looks like del_gendisk should thaw writeback threads, but not
>> > during suspend, only during resume.
>>
>> Thawing the writeback thread only during resume does fix the case
>> Maxim originally presented:
>>
>> 0. build kernel with CONFIG_MMC_UNSAFE_RESUME
>> 1. insert SD card
>> 2. suspend
>> 3. remove SD card while suspended
>> 4. resume from suspend hangs
>>
>> But if CONFIG_MMC_UNSAFE_RESUME is not set, the kernel oopses during
>> suspend because the MMC device suspend times out:
>>
>> mmc0: card e624 removed
>> **** DPM device timeout: pxa2xx-mci.0 (pxa2xx-mci)
>> kernel BUG at /home/mreimer/sdg/android/android-2.1/kernel/drivers/base/power/main.c:453!
>> Unable to handle kernel NULL pointer dereference at virtual address 00000000
>> pgd = c0004000
>> [00000000] *pgd=00000000
>> Internal error: Oops: 817 [#1] PREEMPT
>>
>> If I thaw the writeback thread unconditionally in del_gendisk() then
>> suspend and resume work as expected for both CONFIG_MMC_UNSAFE_RESUME
>> set/not set, even when the card is removed while suspended.
>>
>> So what is the proper fix?
>
> I don't see any reason not to let del_gendisk thaw the writeback thread
> during suspend.  Since the device is going away anyhow, letting the
> thread run shouldn't cause any problems.

So how does the attached patch look?

Matt