Messages in this thread | | | Subject | Re: Hotplug CPU printk issue | From | Rusty Russell <> | Date | Fri, 27 May 2005 12:08:44 +1000 |
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On Thu, 2005-05-26 at 12:32 -0700, David Mosberger wrote: > >>>>> On Wed, 25 May 2005 22:52:04 -0700, Andrew Morton <akpm@osdl.org> said: > > Andrew> Shaohua Li <shaohua.li@intel.com> 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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