* Andrew Morton <[email protected]> wrote:
> > I would be happy to be corrected if the above impression of
> > freeze_processes() is corrected ..
>
> It could be that the freezer needs a bit of work for this application.
> Obviously we're not interested in the handling of disk I/O, so we'd
> really like to do a simple
> try_to_freeze_tasks(FREEZER_USER_SPACE|FREEZER_KERNEL_THREADS), but
> the code isn't set up to do that (it should be). The other non-swsusp
> callers probably want this change as well. But that's all a minor
> matter.
yes. The freezer does the fundamentally right thing: it stops all tasks
in user-space or waits for them to return back to user-space to stop
them there, or if it's a pure kernel-space task it waits until that
kernel-space task voluntarily stop.
Once the system is in such a state, and all processing has been stopped,
all of the kernel's data structures are completely 'unused', and we can:
- patch the kernel freely (kprobes)
- save+stop the kernel (sw-suspend)
- remove a CPU (CPU hotplug and suspend)
- (We could also use this mechanism to live-migrate the kernel to
another system btw., possibly useful for containers)
- (We could also use this mechanism to create a live snapshot of a
running kernel, together with an LVM snapshot of filesystem state,
for possible restore point later on.)
It is a very powerful mechanism that has really nice properties - we
should work on this one shared infrastructure instead of adding zillions
of per-subsystem CPU hotplug locks.
Ingo
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