Re: [3/5] 2.6.21-rc4: known regressions (v2)

Eric W. Biederman
2007-03-25T12:58:31Z

"Rafael J. Wysocki" <rjw@sisk.pl> writes:

> Yes, in kernel/power/disk.c:power_down() .
>
> Please comment out the disable_nonboot_cpus() in there and retest (but please
> test the latest Linus' tree).

<rant>

Why do we even need a disable_nonboot_cpus in that path? machine_shutdown
on i386 and x86_64 should take care of that. Further the code that computes
the boot cpu is bogus (not all architectures require cpu == 0 to be
the boot cpu), and disabling non boot cpus appears to be a strong
x86ism, in the first place.

If the only reason for disable_nonboot_cpus there is to avoid the
WARN_ON in init_low_mappings() we should seriously consider killing
it. If we can wait for 2.6.22 the relocatable x86_64 patchset that
Andi has queued, has changes that kill the init_low_mapping() hack.

I'm not very comfortable with calling cpu_down in a common code path
right now either. I'm fairly certain we still don't have that
correct. So if we confine the mess that is cpu_down to #if
defined(CPU_HOTPLUG) && defined(CONFIG_EXPERIMENTAL) I don't care.
If we start using it everywhere I'm very nervous. I know the irq
migration when bringing a cpu down is strongly racy, and I don't think
we actually put cpus to sleep properly either.

</rant>

Eric