2019-10-30 15:43:25

by Qais Yousef

Subject: [PATCH 03/12] powerpc: Replace cpu_up/down with device_online/offline

The core device API performs extra housekeeping bits that are missing
from directly calling cpu_up/down.

See commit a6717c01ddc2 ("powerpc/rtas: use device model APIs and
serialization during LPM") for an example description of what might go
wrong.

This also prepares to make cpu_up/down a private interface for anything
but the cpu subsystem.

Signed-off-by: Qais Yousef <[email protected]>
CC: Benjamin Herrenschmidt <[email protected]>
CC: Paul Mackerras <[email protected]>
CC: Michael Ellerman <[email protected]>
CC: Enrico Weigelt <[email protected]>
CC: Ram Pai <[email protected]>
CC: Nicholas Piggin <[email protected]>
CC: Thiago Jung Bauermann <[email protected]>
CC: Christophe Leroy <[email protected]>
CC: Thomas Gleixner <[email protected]>
CC: [email protected]
CC: [email protected]
---
arch/powerpc/kernel/machine_kexec_64.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index 04a7cba58eff..ebf8cc7acc4d 100644
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -208,13 +208,15 @@ static void wake_offline_cpus(void)
{
int cpu = 0;

+ lock_device_hotplug();
for_each_present_cpu(cpu) {
if (!cpu_online(cpu)) {
printk(KERN_INFO "kexec: Waking offline cpu %d.\n",
cpu);
- WARN_ON(cpu_up(cpu));
+ WARN_ON(device_online(get_cpu_device(cpu)));
}
}
+ unlock_device_hotplug();
}

static void kexec_prepare_cpus(void)
--
2.17.1

2019-11-19 01:23:57

by Michael Ellerman

Subject: Re: [PATCH 03/12] powerpc: Replace cpu_up/down with device_online/offline

Qais Yousef <[email protected]> writes:
> The core device API performs extra housekeeping bits that are missing
> from directly calling cpu_up/down.
>
> See commit a6717c01ddc2 ("powerpc/rtas: use device model APIs and
> serialization during LPM") for an example description of what might go
> wrong.
>
> This also prepares to make cpu_up/down a private interface for anything
> but the cpu subsystem.
>
> Signed-off-by: Qais Yousef <[email protected]>
> CC: Benjamin Herrenschmidt <[email protected]>
> CC: Paul Mackerras <[email protected]>
> CC: Michael Ellerman <[email protected]>
> CC: Enrico Weigelt <[email protected]>
> CC: Ram Pai <[email protected]>
> CC: Nicholas Piggin <[email protected]>
> CC: Thiago Jung Bauermann <[email protected]>
> CC: Christophe Leroy <[email protected]>
> CC: Thomas Gleixner <[email protected]>
> CC: [email protected]
> CC: [email protected]
> ---
> arch/powerpc/kernel/machine_kexec_64.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)

My initial though is "what about kdump", but that function is not called
during kdump, so there should be no issue with the extra locking leading
to deadlocks in a crash.

Acked-by: Michael Ellerman <[email protected]>

I assume you haven't actually tested it?

cheers

> diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
> index 04a7cba58eff..ebf8cc7acc4d 100644
> --- a/arch/powerpc/kernel/machine_kexec_64.c
> +++ b/arch/powerpc/kernel/machine_kexec_64.c
> @@ -208,13 +208,15 @@ static void wake_offline_cpus(void)
> {
> int cpu = 0;
>
> + lock_device_hotplug();
> for_each_present_cpu(cpu) {
> if (!cpu_online(cpu)) {
> printk(KERN_INFO "kexec: Waking offline cpu %d.\n",
> cpu);
> - WARN_ON(cpu_up(cpu));
> + WARN_ON(device_online(get_cpu_device(cpu)));
> }
> }
> + unlock_device_hotplug();
> }
>
> static void kexec_prepare_cpus(void)
> --
> 2.17.1

2019-11-19 09:49:35

by Qais Yousef

Subject: Re: [PATCH 03/12] powerpc: Replace cpu_up/down with device_online/offline

On 11/19/19 12:19, Michael Ellerman wrote:
> Qais Yousef <[email protected]> writes:
> > The core device API performs extra housekeeping bits that are missing
> > from directly calling cpu_up/down.
> >
> > See commit a6717c01ddc2 ("powerpc/rtas: use device model APIs and
> > serialization during LPM") for an example description of what might go
> > wrong.
> >
> > This also prepares to make cpu_up/down a private interface for anything
> > but the cpu subsystem.
> >
> > Signed-off-by: Qais Yousef <[email protected]>
> > CC: Benjamin Herrenschmidt <[email protected]>
> > CC: Paul Mackerras <[email protected]>
> > CC: Michael Ellerman <[email protected]>
> > CC: Enrico Weigelt <[email protected]>
> > CC: Ram Pai <[email protected]>
> > CC: Nicholas Piggin <[email protected]>
> > CC: Thiago Jung Bauermann <[email protected]>
> > CC: Christophe Leroy <[email protected]>
> > CC: Thomas Gleixner <[email protected]>
> > CC: [email protected]
> > CC: [email protected]
> > ---
> > arch/powerpc/kernel/machine_kexec_64.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
>
> My initial though is "what about kdump", but that function is not called
> during kdump, so there should be no issue with the extra locking leading
> to deadlocks in a crash.
>
> Acked-by: Michael Ellerman <[email protected]>

Thanks.

>
> I assume you haven't actually tested it?

Only compile tested it I'm afraid. Would appreciate if you can give it a spin.
Otherwise I'd be happy to try it out on qemu.

Cheers

--
Qais Yousef