Re: [PATCH] mm: fix lazy vmap purging (use-after-free error)

From: Ingo Molnar
Date: Mon Feb 23 2009 - 04:28:20 EST



* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Mon, 23 Feb 2009 10:07:35 +0100 Ingo Molnar <mingo@xxxxxxx> wrote:
>
> > > ---
> > >
> > > init/main.c | 3 +++
> > > kernel/rcuclassic.c | 4 +++-
> > > kernel/rcutree.c | 4 +++-
> > > 3 files changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/init/main.c b/init/main.c
> > > index 8442094..51f4b71 100644
> > > --- a/init/main.c
> > > +++ b/init/main.c
> > > @@ -121,6 +121,8 @@ static char *static_command_line;
> > > static char *execute_command;
> > > static char *ramdisk_execute_command;
> > >
> > > +int idle_task_is_really_idle; /* set to 1 late in boot. */
> > > +
> > > #ifdef CONFIG_SMP
> > > /* Setup configured maximum number of CPUs to activate */
> > > unsigned int __initdata setup_max_cpus = NR_CPUS;
> > > @@ -463,6 +465,7 @@ static noinline void __init_refok rest_init(void)
> > > * at least once to get things moving:
> > > */
> > > init_idle_bootup_task(current);
> > > + idle_task_is_really_idle = 1;
> > > preempt_enable_no_resched();
> > > schedule();
> > > preempt_disable();
> >
> > Could you please use system_state instead? We could insert a new
> > stage - or just use SYSTEM_RUNNING as the trigger.
>
> I think the standalone flag is better (once those
> extern-decls-in-C get fixed).
>
> system_state's semantics have, err, evolved over time. If
> this happens again (and the patch sneaks past my attention)
> then there's a risk that code which depends upon system_state
> will break - this has happened in the past. Plus piling more
> dependencies on system_state of course makes any evolution of
> its semantics harder to do...

All we need is a SYSTEM_BOOTING_EARLY boundary - prior which
there's no real scheduling yet. I used SYSTEM_SCHEDULER_BOOTING
state before and it worked well and wasnt fragile.

Our system_state semantics problems were more rooted in the fact
that the SYSTEM_BOOTING stage wasnt well defined. But if we did
a SYSTEM_SCHEDULER_BOOTING stage that would be pretty
bit-rot-safe.

Ingo
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