Re: [BUG] Code reordering in swsusp breaks suspend on SMP systems

Pavel Machek
2007-03-21T22:21:31Z

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
>

(Yep, it was in my "to analyze" queue).

> 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.
>

Thanks for detailed explanation.

...but, on my machine suspend works ok in -rc4. I'm not seeing this.

...by design, "frozen" tasks must not hold any locks. If frozen task
holds a lock, that's a bug.

> Or, it is also possible to revert this change.

Are you using xfs?
Pavel
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