Re: [RFC][PATCH -mm][Experimental] swsusp: freeze userspace processes first

Pavel Machek
2006-02-01T12:49:50Z

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Hi!

> > > This is an experimantal patch aimed at the "unable to freeze processes
> > > under load" problem.
> > >
> > > On my box the 2.6.16-rc1-mm4 kernel with this patch applied survives the
> > > "dd if=/dev/hda of=/dev/null" test.
> > >
> > > Please have a look.
> >
> > It makes it better (well, I used my own, simpler variant, but that
> > should not matter; patch is attached). I now can't reproduce hangs
> > with simple stress testing, but running kernel make alongside that
> > makes it hang sometimes. Example of non-frozen gcc:
> >
> > gcc D EEE06A70 0 1750 1749 1751
> > (NOTLB)
> > df85df38 00000046 bf878130 eee06a70 00004111 eee06a70 eee06a70
> > 003d0900
> > 00000000 c0137cf5 df85c000 00000000 c058ada2 c012503e ef2c915c
> > ef2c9030
> > c1c0b480 7c3b8500 003d0927 df85c000 00000a98 7c3b8500 003d0927
> > c0770800
> > Call Trace:
> > [<c0137cf5>] attach_pid+0x25/0xb0
> > [<c058ada2>] _write_unlock_irq+0x12/0x30
> > [<c012503e>] copy_process+0xe5e/0x11b0
> > [<c0588f74>] wait_for_completion+0x94/0xd0
> > [<c0121690>] default_wake_function+0x0/0x10
> > [<c01254d9>] do_fork+0x149/0x210
> > [<c0101218>] sys_vfork+0x28/0x30
> > [<c0103231>] syscall_call+0x7/0xb
> >
> > ...maybe solving this would solve journalling problems, too? It is
> > similar AFAICT.
>
> What exactly is the journalling problem?

Hangs by freezing everything at same time only happen with journalling
filesystems; there kjournald needs to be running if we want user
threads to be stoppable.

> > @@ -87,7 +87,6 @@ static int prepare_processes(void)
> > int error;
> >
> > pm_prepare_console();
> > - sys_sync();
> > disable_nonboot_cpus();
> >
> > if (freeze_processes()) {
>
> That will help speed up freezing, but it won't help the integrity of your data
> if you don't resume.

See the patch better; it is now done between freezing userspace and
kernel threads.

> > /*
> > * Timeout for stopping processes
> > */
> > -#define TIMEOUT (6 * HZ)
> > +#define TIMEOUT (60 * HZ)
>
> You're kidding, right?

sync takes long time... and 6 seconds were not enough to deliver
signals on highly-loaded ext2.
Pavel

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Thanks, Sharp!