[PATCH] powerpc/powernv: force all CPUs to be bootable

[PATCH] powerpc/powernv: force all CPUs to be bootable

[Greg Kurz]

The subcore logic needs all the CPUs declared in the DT to be bootable,
otherwise the kernel hangs at boot time. Since subcore support starts
with POWER8, we can keep the current behaviour for older CPUs.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---

Since smt-enabled is still needed by Freescale, the choice was made to fix
powernv only. I could test that smt-enabled is still honored on POWER7 and
ignored on POWER8, as expected.

 arch/powerpc/platforms/powernv/smp.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/smp.c b/arch/powerpc/platforms/powernv/smp.c
index b716f66..5b6e002 100644
--- a/arch/powerpc/platforms/powernv/smp.c
+++ b/arch/powerpc/platforms/powernv/smp.c
@@ -198,13 +198,24 @@ static void pnv_smp_cpu_kill_self(void)
 
 #endif /* CONFIG_HOTPLUG_CPU */
 
+static int pnv_cpu_bootable(unsigned int nr)
+{
+	/* Starting with POWER8, all CPUs need to be booted to avoid hangs
+	 * during subcore init.
+	 */
+	if (cpu_has_feature(CPU_FTR_ARCH_207S))
+		return 1;
+
+	return smp_generic_cpu_bootable(nr);
+}
+
 static struct smp_ops_t pnv_smp_ops = {
 	.message_pass	= smp_muxed_ipi_message_pass,
 	.cause_ipi	= NULL,	/* Filled at runtime by xics_smp_probe() */
 	.probe		= xics_smp_probe,
 	.kick_cpu	= pnv_smp_kick_cpu,
 	.setup_cpu	= pnv_smp_setup_cpu,
-	.cpu_bootable	= smp_generic_cpu_bootable,
+	.cpu_bootable	= pnv_cpu_bootable,
 #ifdef CONFIG_HOTPLUG_CPU
 	.cpu_disable	= pnv_smp_cpu_disable,
 	.cpu_die	= generic_cpu_die,

Re: [PATCH] powerpc/powernv: force all CPUs to be bootable

[Greg Kurz]

On Fri, 12 Dec 2014 12:37:40 +0100
Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:

> The subcore logic needs all the CPUs declared in the DT to be bootable,
> otherwise the kernel hangs at boot time. Since subcore support starts
> with POWER8, we can keep the current behaviour for older CPUs.
> 
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---
> 
> Since smt-enabled is still needed by Freescale, the choice was made to fix
> powernv only. I could test that smt-enabled is still honored on POWER7 and
> ignored on POWER8, as expected.
> 

FWIW I get plenty (for nearly all vcpus) the following dump when booting a
PowerKVM guest on a virtio-blk disk with smt-enabled=off:

[   10.535151] kobject '(null)' (c0000007ff260c18): tried to add an uninitialized object, something is seriously wrong.
[   10.535538] CPU: 12 PID: 708 Comm: systemd-udevd Not tainted 3.18.0-rc3+ #3
[   10.535779] Call Trace:
[   10.535886] [c0000000ff0e38f0] [c0000000007a1db8] dump_stack+0x90/0xbc (unreliable)
[   10.536242] [c0000000ff0e3920] [c0000000003c5504] kobject_add+0xc4/0xd0
[   10.536593] [c0000000ff0e39a0] [c00000000039df20] blk_mq_register_hctx+0xd0/0x100
[   10.536930] [c0000000ff0e3a20] [c00000000039ed0c] blk_mq_sysfs_register+0x5c/0xb0
[   10.537257] [c0000000ff0e3a50] [c00000000039b694] blk_mq_queue_reinit_notify+0xc4/0x110
[   10.537594] [c0000000ff0e3a90] [c0000000000c5388] notifier_call_chain+0x88/0x100
[   10.537942] [c0000000ff0e3ae0] [c00000000009e264] cpu_notify+0x34/0x80
[   10.538227] [c0000000ff0e3b00] [c00000000009e794] _cpu_up+0x204/0x210
[   10.538519] [c0000000ff0e3bb0] [c00000000009e8ac] cpu_up+0x10c/0x130
[   10.538796] [c0000000ff0e3c30] [c00000000062121c] cpu_subsys_online+0x5c/0xe0
[   10.539089] [c0000000ff0e3c80] [c0000000004bf0e4] device_online+0xb4/0x120
[   10.539370] [c0000000ff0e3cc0] [c0000000004bf1f4] online_store+0xa4/0xb0
[   10.539651] [c0000000ff0e3d00] [c0000000004bb744] dev_attr_store+0x34/0x60
[   10.539929] [c0000000ff0e3d20] [c0000000003038c4] sysfs_kf_write+0x64/0xa0
[   10.540217] [c0000000ff0e3d40] [c000000000302940] kernfs_fop_write+0x140/0x1d0
[   10.540553] [c0000000ff0e3d90] [c00000000026ac64] vfs_write+0xd4/0x260
[   10.540831] [c0000000ff0e3de0] [c00000000026b780] SyS_write+0x60/0x110
[   10.541131] [c0000000ff0e3e30] [c0000000000091fc] syscall_exit+0x0/0x7c

It seems that split core isn't the only code that gets affected by smt-enabled.
Should we drop cpu_bootable for pseries ?

Cheers.

--
Greg

>  arch/powerpc/platforms/powernv/smp.c |   13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/smp.c b/arch/powerpc/platforms/powernv/smp.c
> index b716f66..5b6e002 100644
> --- a/arch/powerpc/platforms/powernv/smp.c
> +++ b/arch/powerpc/platforms/powernv/smp.c
> @@ -198,13 +198,24 @@ static void pnv_smp_cpu_kill_self(void)
>  
>  #endif /* CONFIG_HOTPLUG_CPU */
>  
> +static int pnv_cpu_bootable(unsigned int nr)
> +{
> +	/* Starting with POWER8, all CPUs need to be booted to avoid hangs
> +	 * during subcore init.
> +	 */
> +	if (cpu_has_feature(CPU_FTR_ARCH_207S))
> +		return 1;
> +
> +	return smp_generic_cpu_bootable(nr);
> +}
> +
>  static struct smp_ops_t pnv_smp_ops = {
>  	.message_pass	= smp_muxed_ipi_message_pass,
>  	.cause_ipi	= NULL,	/* Filled at runtime by xics_smp_probe() */
>  	.probe		= xics_smp_probe,
>  	.kick_cpu	= pnv_smp_kick_cpu,
>  	.setup_cpu	= pnv_smp_setup_cpu,
> -	.cpu_bootable	= smp_generic_cpu_bootable,
> +	.cpu_bootable	= pnv_cpu_bootable,
>  #ifdef CONFIG_HOTPLUG_CPU
>  	.cpu_disable	= pnv_smp_cpu_disable,
>  	.cpu_die	= generic_cpu_die,
> 
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