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SubjectRe: Possible regression? 2.6.26-rc1: T61s failure after suspend/resume
On Fri, May 09, 2008 at 05:21:14PM +0100, Hugh Dickins wrote:
> On Fri, 9 May 2008, Glauber Costa wrote:
> >
> > I can't reproduce it neither, and looking at the code over and over
> > again, see no obvious point for the breakage. I'll try to reproduce it
> > myself,
> > to see if I can spot something. But correct me if I'm wrong, this is
> > all 64-bit machines, right?
> >
> > I'm stuck with mostly 32-bit hardware, but will give it a try anyway.
> The machine is 64-bit capable (Core2 Duo), but the kernels I'm running
> for this are 32-bit, so I doubt that the 64-bitability is relevant.
> I'd love to see what happens with a 64-bit kernel, but I never get
> back from suspend with it (and that's not a recent regression).
> Carlos is also seeing this with a 32-bit kernel (on P4 Xeon with HT).
> Please don't take my git bisection result too seriously: that's where
> it led when I fudged things around enough, and treated blank screens
> as manifestations of the problem, which very likely they're not
> (there's some other bug which makes it very variable how quickly
> I resume). And also, I wasn't checking how many cpus came up each
> time: I wouldn't be surprised if at some points in your series only
> one would come up, which would then look like a "good" point to me.

For 64bit kernels this commit seems to be a nop, but not for
32bit kernels.

Looking at commit 4fe29a85642544503cf81e9cf251ef0f4e65b162 it contained
two changes for 32bit SMP kernels:
- it enables the previously not enabled HAVE_SETUP_PER_CPU_AREA
- the following hunk:

--- a/arch/x86/kernel/smpboot_32.c
+++ b/arch/x86/kernel/smpboot_32.c
@@ -665,6 +665,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu)
cpu_clear(cpu, cpu_callout_map); /* was set here (do_boot_cpu()) */
cpu_clear(cpu, cpu_initialized); /* was set by cpu_init() */
+ cpu_clear(cpu, cpu_possible_map);
} else {
per_cpu(x86_cpu_to_apicid, cpu) = apicid;
@@ -743,6 +744,7 @@ EXPORT_SYMBOL(xquad_portio);

static void __init disable_smp(void)
+ cpu_possible_map = cpumask_of_cpu(0);
phys_cpu_present_map = physid_mask_of_physid(0);

Before assuming the bisection pointed to a wrong commit it might be
worth checking these.

I don't understand why these were mixed into a commit that
moved much stuff previously only used on 64bit kernels from
arch/x86/kernel/setup64.c to arch/x86/kernel/setup.c ...

> Thanks,
> Hugh



"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed

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