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Subject[PATCH] arch/arm64: Fix topology initialization for core scheduling
Date
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 <pauld@redhat.com>
---
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
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