[bug] Re: [PATCH] - Fix stack overflow for large values of MAX_APICS

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> wrote:

> * Jack Steiner <steiner@sgi.com> wrote:
> 
> > physid_mask_of_physid() causes a huge stack (12k) to be created if 
> > the number of APICS is large. Replace physid_mask_of_physid() with a 
> > new function that does not create large stacks. This is a problem 
> > only on large x86_64 systems.
> 
> this indeed fixes the crash i reported here:
> 
>    http://lkml.org/lkml/2008/6/19/98
> 
> so i've added both this and the MAXAPICS patch to tip/x86/uv, and will 
> test it some more. Lets hope it goes all well this time :-)

-tip auto-testing found a new boot failure on x86 which happens if 
NR_CPUS is changed from 8 to 4096. The hang goes like this:

 Linux version 2.6.26-rc7-tip (mingo@dione) (gcc version 4.2.3) #10233 SMP
 Tue Jun 24 12:13:46 CEST 2008
 [...]
 initcall init_mnt_writers+0x0/0x8c returned 0 after 0 msecs
 calling  eventpoll_init+0x0/0x9a
 initcall eventpoll_init+0x0/0x9a returned 0 after 0 msecs
 calling  anon_inode_init+0x0/0x11a
 initcall anon_inode_init+0x0/0x11a returned 0 after 0 msecs
 calling  pcie_aspm_init+0x0/0x27
 initcall pcie_aspm_init+0x0/0x27 returned 0 after 0 msecs
 calling  acpi_event_init+0x0/0x57
 [... hard hang ...]

on a good bootup, it would continue like this:

 initcall acpi_event_init+0x0/0x57 returned 0 after 38 msecs
 calling  pnp_system_init+0x0/0x17
 [...]

the config, full bootlog and reproducer bzImage is at:

  http://redhat.com/~mingo/misc/config-Tue_Jun_24_07_44_17_CEST_2008.bad
  http://redhat.com/~mingo/misc/log-Tue_Jun_24_07_44_17_CEST_2008.bad
  http://redhat.com/~mingo/misc/bzImage-Tue_Jun_24_07_44_17_CEST_2008.bad

changing CONFIG_NR_CPUS from 4096 to 8 causes the system to boot up 
fine.

	Ingo