x86: fix cpu hotplug crash
authorZhang, Yanmin <yanmin_zhang@linux.intel.com>
Tue, 24 Jun 2008 08:06:23 +0000 (16:06 +0800)
committerIngo Molnar <mingo@elte.hu>
Mon, 30 Jun 2008 11:15:43 +0000 (13:15 +0200)
commitfcb43042ef55d2f46b0efa5d7746967cef38f056
tree21aa270c236fe572c377eb16337d77be8e5d4362
parent0b1faeef5f9243bb5fc5713a34bbf1ceab0de562
x86: fix cpu hotplug crash

Vegard Nossum reported crashes during cpu hotplug tests:

  http://marc.info/?l=linux-kernel&m=121413950227884&w=4

In function _cpu_up, the panic happens when calling
__raw_notifier_call_chain at the second time. Kernel doesn't panic when
calling it at the first time. If just say because of nr_cpu_ids, that's
not right.

By checking the source code, I found that function do_boot_cpu is the culprit.
Consider below call chain:
 _cpu_up=>__cpu_up=>smp_ops.cpu_up=>native_cpu_up=>do_boot_cpu.

So do_boot_cpu is called in the end. In do_boot_cpu, if
boot_error==true, cpu_clear(cpu, cpu_possible_map) is executed. So later
on, when _cpu_up calls __raw_notifier_call_chain at the second time to
report CPU_UP_CANCELED, because this cpu is already cleared from
cpu_possible_map, get_cpu_sysdev returns NULL.

Many resources are related to cpu_possible_map, so it's better not to
change it.

Below patch against 2.6.26-rc7 fixes it by removing the bit clearing in
cpu_possible_map.

Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com>
Tested-by: Vegard Nossum <vegard.nossum@gmail.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
arch/x86/kernel/smpboot.c