On Mon, Jul 22, 2013 at 5:32 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Jul 22, 2013 at 4:55 PM, Colin Cross <ccross@xxxxxxxxxxx> wrote:
>>
>> I think the right solution is to add a flag to the freezing task that
>> marks it unfreezable. I think PF_NOFREEZE would work, although it is
>> normally used on kernel threads, can you see if the attached patch
>> helps?
>
> Hmm. That does seem to be the right thing to do, but I wonder about
> the *other* callers of freeze_processes() IOW, kexec and friends.
>
> So maybe we should do this in {freeze|thaw}_processes() itself, and
> just make the rule be that the caller of freeze_processes() itself is
> obviously not frozen, and has to be the same one that then thaws
> things?
>
> Colin? Rafael? Comments?
>
> Linus
I was worried about clearing the flag in thaw_processes(). If a
kernel thread with PF_NOFREEZE set ever called thaw_processes(), which
autosleep might do, it would clear the flag. Or if a different thread
called freeze_processes() and thaw_processes(). All the other callers
besides the SNAPSHOT_FREEZE ioctl stay in the kernel between
freeze_processes() and thaw_processes(), which makes the fanout of
places that could call try_to_freeze() much more controllable.
Using a new flag that operates like PF_NOFREEZE but doesn't conflict
with it, or a nofreeze_depth counter, would also work.
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