On Thu, Feb 26, 2015 at 8:00 PM, Stephen Warren [off-list ref] wrote:

On 02/26/2015 10:42 AM, Russell King - ARM Linux wrote:

quoted

On Thu, Feb 26, 2015 at 11:37:08AM +0100, Geert Uytterhoeven wrote:

quoted

When trying to kexec into a new kernel on a platform where multiple CPU
cores are present, but no SMP bringup code is available yet, the
kexec_load system call fails with:

     kexec_load failed: Invalid argument

The SMP test added to machine_kexec_prepare() in commit 2103f6cba61a8b8b
("ARM: 7807/1: kexec: validate CPU hotplug support") wants to prohibit
kexec on SMP platforms where it cannot disable secondary CPUs.
However, this test is too strict: if the secondary CPUs couldn't be
enabled in the first place, there's no need to disable them later at
kexec time.  Hence skip the test in the absence of SMP bringup code.

Hmm.  I don't think we should relax it in this manner - I think there's
an easier solution to this.

quoted

diff --git a/arch/arm/kernel/machine_kexec.c

b/arch/arm/kernel/machine_kexec.c
index de2b085ad7535da7..8bf3b7c098881b95 100644

--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c

@@ -46,7 +46,8 @@ int machine_kexec_prepare(struct kimage *image)
         * and implements CPU hotplug for the current HW. If not, we

won't be
         * able to kexec reliably, so fail the prepare operation.
         */
-       if (num_possible_cpus() > 1 && !platform_can_cpu_hotplug())
+       if (num_possible_cpus() > 1 && platform_can_secondary_boot() &&
+           !platform_can_cpu_hotplug())

        if (num_online_cpus() > 1 && !platform_can_cpu_hotplug())

I can't remember the call stack here. Is num_online_cpus() guaranteed not to
change from this point through to when the kexec actually happens?

Yeah, I had similar thoughts when I added the new test.

include/linux/cpumask.h:
 *     cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
 *     cpu_present_mask - has bit 'cpu' set iff cpu is populated
 *     cpu_online_mask  - has bit 'cpu' set iff cpu available to scheduler
 *     cpu_active_mask  - has bit 'cpu' set iff cpu available to migration

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds