From: Phil Auld pauld@redhat.com
[ Upstream commit 5524cbb1bfcdff0cad0aaa9f94e6092002a07259 ]
Arm64 systems rely on store_cpu_topology() to call update_siblings_masks() to transfer the toplogy to the various cpu masks. This needs to be done before the call to notify_cpu_starting() which tells the scheduler about each cpu found, otherwise the core scheduling data structures are setup in a way that does not match the actual topology.
With smt_mask not setup correctly we bail on `cpumask_weight(smt_mask) == 1` for !leaders in:
notify_cpu_starting() cpuhp_invoke_callback_range() sched_cpu_starting() sched_core_cpu_starting()
which leads to rq->core not being correctly set for !leader-rq's.
Without this change stress-ng (which enables core scheduling in its prctl tests in newer versions -- i.e. with PR_SCHED_CORE support) 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 Reviewed-by: Dietmar Eggemann dietmar.eggemann@arm.com Tested-by: Dietmar Eggemann dietmar.eggemann@arm.com Link: https://lore.kernel.org/r/20220331153926.25742-1-pauld@redhat.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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);
/*