Hi,
Starting with 2.6.21-rc1 suspend to ram and disk doesn't work anymore on my
system.
I did a git-bisect and found that those commits break it:
e3c7db621bed4afb8e231cb005057f2feb5db557 - [PATCH] [PATCH] PM: Change code
ordering in main.c
ed746e3b18f4df18afa3763155972c5835f284c5 - [PATCH] [PATCH] swsusp: Change code
ordering in disk.c
259130526c267550bc365d3015917d90667732f1 - [PATCH] [PATCH] swsusp: Change code
ordering in user.c
I already reported about it, but now i know the reason why suspend breaks.
The problem is that both cpu_up/cpu_down were allowed to sleep until now,
and it did work because those functions could be called only in process context
(the one that writes to /sys/devices/system/cpu/cpu*/online) or idle thread
that does smp_init()).
But now they are called _after_ all tasks were suspended, so if cpu_down tries
for example to take a lock
that is taken by different process, it can't since the different proccess is
frozen and can't release the lock.
I tested this and all results are positive:
I disabled 2nd cpu by hand, and then suspend to ram was successfull.
Suspend to disk went correctly, but it hang on resume, and I know why.
It hang in old kernel trying to disable 2nd cpu that was enabled by it.
I was able using kdb to confirm that this is true because it was still possible
to enter kdb, and see that
idle thread (swapper) was active, and uswsusp was waiting on mutex inside
workqueue_cpu_callback.
The solution for this problem seems to be ether complete audit of code that
uses register_cpu_notifier,
to ensure that it doesn't sleep.
Also documentation should be changed to note about it.
Or, it is also possible to revert this change.
Regards,
Maxim Levitsky
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