Some arm64 rely on store_cpu_topology() to setup the real topology.
This needs to be done before the call to notify_cpu_starting() which
tell the scheduler about the cpu otherwise the core scheduling data
structures are setup in a way that does not match the actual topology.
Without this change stress-ng (which enables core scheduling in its prctl
tests) causes a warning and then a crash (trimmed for legibility):
[ 1853.805168] ------------[ cut here ]------------
[ 1853.809784] task_rq(b)->core != rq->core
[ 1853.809792] WARNING: CPU: 117 PID: 0 at kernel/sched/fair.c:11102 cfs_prio_less+0x1b4/0x1c4
...
[ 1854.015210] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
...
[ 1854.231256] Call trace:
[ 1854.233689] pick_next_task+0x3dc/0x81c
[ 1854.237512] __schedule+0x10c/0x4cc
[ 1854.240988] schedule_idle+0x34/0x54
Fixes: 9edeaea1bc45 ("sched: Core-wide rq->lock")
Signed-off-by: Phil Auld <[email protected]>
---
This is a similar issue to
f2703def339c ("MIPS: smp: fill in sibling and core maps earlier")
which fixed it for MIPS.
arch/arm64/kernel/smp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 27df5c1e6baa..3b46041f2b97 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -234,6 +234,7 @@ asmlinkage notrace void secondary_start_kernel(void)
* Log the CPU info before it is marked online and might get read.
*/
cpuinfo_store_cpu();
+ store_cpu_topology(cpu);
/*
* Enable GIC and timers.
@@ -242,7 +243,6 @@ asmlinkage notrace void secondary_start_kernel(void)
ipi_setup(cpu);
- store_cpu_topology(cpu);
numa_add_cpu(cpu);
/*
--
2.18.0
On 22/03/2022 17:03, Phil Auld wrote:
> Some arm64 rely on store_cpu_topology() to setup the real topology.
> This needs to be done before the call to notify_cpu_starting() which
> tell the scheduler about the cpu otherwise the core scheduling data
> structures are setup in a way that does not match the actual topology.
>
> Without this change stress-ng (which enables core scheduling in its prctl
> tests) causes a warning and then a crash (trimmed for legibility):
>
> [ 1853.805168] ------------[ cut here ]------------
> [ 1853.809784] task_rq(b)->core != rq->core
> [ 1853.809792] WARNING: CPU: 117 PID: 0 at kernel/sched/fair.c:11102 cfs_prio_less+0x1b4/0x1c4
> ...
> [ 1854.015210] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
> ...
> [ 1854.231256] Call trace:
> [ 1854.233689] pick_next_task+0x3dc/0x81c
> [ 1854.237512] __schedule+0x10c/0x4cc
> [ 1854.240988] schedule_idle+0x34/0x54
>
> Fixes: 9edeaea1bc45 ("sched: Core-wide rq->lock")
> Signed-off-by: Phil Auld <[email protected]>
> ---
> This is a similar issue to
> f2703def339c ("MIPS: smp: fill in sibling and core maps earlier")
> which fixed it for MIPS.
I assume this is for a machine which relies on MPIDR-based setup
(package_id == -1)? I.e. it doesn't have proper ACPI/(DT) data for
topology setup.
Tried on a ThunderX2 by disabling parse_acpi_topology() but then I end
up with a machine w/o SMT, so `stress-ng --prctl N` doesn't show this issue.
Which machine were you using?
> arch/arm64/kernel/smp.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 27df5c1e6baa..3b46041f2b97 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -234,6 +234,7 @@ asmlinkage notrace void secondary_start_kernel(void)
> * Log the CPU info before it is marked online and might get read.
> */
> cpuinfo_store_cpu();
> + store_cpu_topology(cpu);
>
> /*
> * Enable GIC and timers.
> @@ -242,7 +243,6 @@ asmlinkage notrace void secondary_start_kernel(void)
>
> ipi_setup(cpu);
>
> - store_cpu_topology(cpu);
> numa_add_cpu(cpu);
>
> /*
On Tue, Mar 29, 2022 at 04:02:22PM +0200 Dietmar Eggemann wrote:
> On 22/03/2022 17:03, Phil Auld wrote:
> > Some arm64 rely on store_cpu_topology() to setup the real topology.
> > This needs to be done before the call to notify_cpu_starting() which
> > tell the scheduler about the cpu otherwise the core scheduling data
> > structures are setup in a way that does not match the actual topology.
> >
> > Without this change stress-ng (which enables core scheduling in its prctl
> > tests) causes a warning and then a crash (trimmed for legibility):
> >
> > [ 1853.805168] ------------[ cut here ]------------
> > [ 1853.809784] task_rq(b)->core != rq->core
> > [ 1853.809792] WARNING: CPU: 117 PID: 0 at kernel/sched/fair.c:11102 cfs_prio_less+0x1b4/0x1c4
> > ...
> > [ 1854.015210] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
> > ...
> > [ 1854.231256] Call trace:
> > [ 1854.233689] pick_next_task+0x3dc/0x81c
> > [ 1854.237512] __schedule+0x10c/0x4cc
> > [ 1854.240988] schedule_idle+0x34/0x54
> >
> > Fixes: 9edeaea1bc45 ("sched: Core-wide rq->lock")
> > Signed-off-by: Phil Auld <[email protected]>
> > ---
> > This is a similar issue to
> > f2703def339c ("MIPS: smp: fill in sibling and core maps earlier")
> > which fixed it for MIPS.
>
> I assume this is for a machine which relies on MPIDR-based setup
> (package_id == -1)? I.e. it doesn't have proper ACPI/(DT) data for
> topology setup.
Yes, that's my understanding. No PPTT.
>
> Tried on a ThunderX2 by disabling parse_acpi_topology() but then I end
> up with a machine w/o SMT, so `stress-ng --prctl N` doesn't show this issue.
>
> Which machine were you using?
This instance is an HPE Apollo 70 set to smt-4. I believe it's ThunderX2
chips.
ARM (CN9980-2200LG4077-Y21-G)
Thanks,
Phil
>
> > arch/arm64/kernel/smp.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index 27df5c1e6baa..3b46041f2b97 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -234,6 +234,7 @@ asmlinkage notrace void secondary_start_kernel(void)
> > * Log the CPU info before it is marked online and might get read.
> > */
> > cpuinfo_store_cpu();
> > + store_cpu_topology(cpu);
> >
> > /*
> > * Enable GIC and timers.
> > @@ -242,7 +243,6 @@ asmlinkage notrace void secondary_start_kernel(void)
> >
> > ipi_setup(cpu);
> >
> > - store_cpu_topology(cpu);
> > numa_add_cpu(cpu);
> >
> > /*
>
--