On Thu, 2005-05-26 at 12:32 -0700, David Mosberger wrote:
> >>>>> On Wed, 25 May 2005 22:52:04 -0700, Andrew Morton <[email protected]> said:
>
> Andrew> Shaohua Li <[email protected]> wrote:
>
> >> > Please confirm that we in fact do not want to allow downed CPUs to
> >> > print things, then send a patch.
> >> Yep. In the cpu hotplug case, per-cpu data possibly isn't initialized
> >> even the system state is 'running'. As the comments say in the original
> >> code, some console drivers assume per-cpu resources have been allocated.
> >> radeon fb is one such driver, which uses kmalloc. After a CPU is down,
> >> the per-cpu data of slab is freed, so the system crashed when printing
> >> some info.
>
> Andrew> hm, that certainly sounds sane, but I do recall there were
> Andrew> reasonable-sounding reasons why the ia64 guys wanted
> Andrew> printk-on-a-down-CPU to work. Hopefully David can remember
> Andrew> what the problem was so we can find a more thorough fix.
>
> I don't recall having submitted such a patch. According to the bk
> log, it was Rusty who added the !system_running check (which was later
> changed to system_state != SYSTEM_RUNNING).
>
> The changelog only says:
>
> "- Allow printk on down cpus once system is running"
IIRC it was a great aid to debugging hotplug CPU, and there seemed no
reason to ban it. I mean, you have to be running code on a down CPU,
which implies you're in arch code or you've done something wrong... I
don't have religious attachment to it, however!
Cheers,
Rusty.
--
A bad analogy is like a leaky screwdriver -- Richard Braakman
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