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    SubjectRe: [PATCH 1/8] Enhance process freezer interface for usage beyond software suspend
    Date
    On Saturday, 7 April 2007 00:20, Nigel Cunningham wrote:
    > Hi.
    >
    > On Fri, 2007-04-06 at 16:34 +0200, Rafael J. Wysocki wrote:
    > > On Monday, 2 April 2007 22:51, Pavel Machek wrote:
    > > > Hi!
    > > >
    > > > > > > +/* Per process freezer specific flags */
    > > > > > > +#define PF_FE_SUSPEND 0x00008000 /* This thread should not be frozen
    > > > > > > + * for suspend
    > > > > > > + */
    > > > > > > +
    > > > > > > +#define PF_FE_KPROBES 0x00000010 /* This thread should not be frozen
    > > > > > > + * for Kprobes
    > > > > > > + */
    > > > > >
    > > > > > Just put the comment before the define for long comments?
    > > > >
    > > > > Agreed.
    > > >
    > > > (Actually it would be nice to say
    > > >
    > > > /* This thread should not be frozen for suspend, becuase it is needed
    > > > for getting image saved to disk */
    > > >
    > > > > > > -#ifdef CONFIG_PM
    > > > > > > +#if defined(CONFIG_PM) || defined(CONFIG_HOTPLUG_CPU) || \
    > > > > > > + defined(CONFIG_KPROBES)
    > > > > >
    > > > > > Should we create CONFIG_FREEZER?
    > > > >
    > > > > Why do you think so? I think the freezer should be compiled automatically
    > > > > if any of the above is set, which is what this directive really means.
    > > >
    > > > Kconfig can do that. ("select statement"). If we have one such ifdef,
    > > > it is okay, but if it would be more of them.
    > > >
    > > > > > Hmmm, I do not really like softlockup watchdog running during suspend.
    > > > > > Can we make this freezeable and make watchdog shut itself off while
    > > > > > suspending?
    > > > >
    > > > > Generally, I agree, but this patch only replaces the existing instances
    > > > > of PF_NOFREEZE with the new mechanism. The changes you're talking about
    > > > > require a separate patch series (or at least one separate patch), I think, and
    > > > > they need not be so simple to make.
    > > >
    > > > Agreed about separate patch series.
    > > >
    > > > > > > - current->flags |= PF_NOFREEZE;
    > > > > > > + freezer_exempt(FE_ALL);
    > > > > > > pid = kernel_thread(do_linuxrc, "/linuxrc", SIGCHLD);
    > > > > > > if (pid > 0) {
    > > > > > > while (pid != sys_wait4(-1, NULL, 0, NULL))
    > > > > >
    > > > > > Does this mean we have userland /linuxrc running with PF_NOFREEZE?
    > > > > > That would be very bad...
    > > > >
    > > > > No, actually it is _required_ for the userland resume to work. Well, perhaps
    > > > > I should place a comment in there so that I don't have to explain this again
    > > > > and again. :-)
    > > >
    > > > Can you put big bold comment there?
    > > >
    > > > Why is it needed? Freezer never freezes _current_ task.
    > >
    > > No, it doesn't, but this task spawns linuxrc and then calls sys_wait4() in a
    > > loop.
    > >
    > > Well, actually, I'll try to plant try_to_freeze() in this loop and see if that
    > > works. If it doesn't, I'll add a comment.
    >
    > It works. I've had:
    >
    > while (pid != sys_wait4(-1, NULL, 0, NULL)) {
    > yield();
    > try_to_freeze();
    > }
    >
    > there for ages for Suspend2.

    OK, thanks. Is there any particular reason to place try_to_freeze() after
    yield()?

    Greetings,
    Rafael
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