Re: Re: Hotplug events during sleep transition

Pavel Machek
2005-12-24T15:28:14Z

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On So 24-12-05 10:11:13, Alan Stern wrote:
> On Fri, 23 Dec 2005, Greg KH wrote:
>
> > On Fri, Dec 23, 2005 at 04:22:44PM -0500, Alan Stern wrote:
> > > On Fri, 23 Dec 2005, Pavel Machek wrote:
> > >
> > > > Well, if you can find some elegant solution in the core, I think thats
> > > > the best way.
> > > >
> > > > You could set system_state to "suspending" or something like that, and
> > > > just if() out notifications in that case.
> > >
> > > How about simply adding a call to try_to_freeze() somewhere inside
> > > kernel/kmod.c:____call_usermodehelper()? That ought to do pretty much
> > > what I want, in theory. The hotplug processes would get frozen before
> > > /sbin/hotplug is exec'ed.
> >
> > On modern distros, /sbin/hotplug is set to NULL, so this isn't an issue.
> > We use netlink to send the data out, so this might not even be a problem
> > anymore...
>
> Indeed it might not. On my older FC3 system I end up with unwanted
> processes, but under FC4 that doesn't happen. (Note however that even on
> the FC4 system, /sbin/hotplug is not empty and /proc/sys/kernel/hotplug
> does point to /sbin/hotplug.)
>
> The ideal situation would be to have PF_FREEZE automatically set for every
> new process created while userspace was frozen. Kernel threads could
> remove the flag and set PF_NOFREEZE if they wanted, while user processes
> would automatically get frozen before returning to userspace. This
> approach would eliminate all the loopholes at once.

It would also prevent some clever stuff with u-swsusp. We'll want to
keep u-swsusp program controlling suspend. I don't see how it needs to
exec() today, but eventually it may want to run some properly-audited
helpers...

...okay, better not, because that would mean memory allocation while
suspended => bad.

Anyway, doing check in exec() or something like that would slow down
hot path. Just take fix userland exec's during suspend one-by-one. We
are doing something wrong if we attempt that, anyway.

Pavel
--
Thanks, Sharp!