Re: v2.6.26-rc7: BUG: unable to handle kernel NULL pointer dereference

Ingo Molnar
2008-06-30T11:25:16Z

* Rusty Russell <rusty@rustcorp.com.au> wrote:

> On Tuesday 24 June 2008 18:06:23 Zhang, Yanmin wrote:

> > 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 source codes, I find 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.
> >
> > Vegard, would you like to help test it?
> >
> > ﻿﻿﻿Signed-off-by: Zhang Yanmin ﻿<yanmin_zhang@linux.intel.com>
[...]

> Nice catch. Basically, cpu_possible_map should only be cleared at
> boot, and probably not even then.
>
> Acked-by: Rusty Russell <rusty@rustcorp.com.au>

applied to tip/x86/urgent for v2.6.26 merging - thanks everyone!

Ingo