[PATCH linux-next v2] powerpc: init jump label early in ppc 64

[zhouzhouyi at gmail.com]

From: Zhouyi Zhou <zhouzhouyi at gmail.com>

In ppc 64, invoke jump_label_init in setup_feature_keys is too late
because static key will be used in subroutine of parse_early_param
which is again subroutine of early_init_devtree.

So we invoke jump_label_init just before parse_early_param in
early_init_devtree. 

Suggested-by: Michael Ellerman <mpe at ellerman.id.au>
Signed-off-by: Zhouyi Zhou <zhouzhouyi at gmail.com>
---
Dear PPC developers

I found this bug when trying to do rcutorture tests in ppc VM of
Open Source Lab of Oregon State University.

qemu-system-ppc64 -nographic -smp cores=8,threads=1 -net none -M pseries -nodefaults -device spapr-vscsi -serial file:/home/ubuntu/linux-next/tools/testing/selftests/rcutorture/res/2022.07.19-01.18.42-torture/results-rcutorture/TREE03/console.log -m 512 -kernel /home/ubuntu/linux-next/tools/testing/selftests/rcutorture/res/2022.07.19-01.18.42-torture/results-rcutorture/TREE03/vmlinux -append "debug_boot_weak_hash panic=-1 console=ttyS0 rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcutorture.onoff_interval=200 rcutorture.onoff_holdoff=30 rcutree.gp_preinit_delay=12 rcutree.gp_init_delay=3 rcutree.gp_cleanup_delay=3 rcutree.kthread_prio=2 threadirqs tree.use_softirq=0 rcutorture.n_barrier_cbs=4 rcutorture.stat_interval=15 rcutorture.shutdown_secs=420 rcutorture.test_no_idle_hz=1 rcutorture.verbose=1"

console.log report following WARN:
[    0.000000][    T0] static_key_enable_cpuslocked(): static key '0xc000000002953260' used before call to jump_label_init()^M
[    0.000000][    T0] WARNING: CPU: 0 PID: 0 at kernel/jump_label.c:166 static_key_enable_cpuslocked+0xfc/0x120^M
[    0.000000][    T0] Modules linked in:^M
[    0.000000][    T0] CPU: 0 PID: 0 Comm: swapper Not tainted 5.19.0-rc5-next-20220708-dirty #131^M
[    0.000000][    T0] NIP:  c00000000038068c LR: c000000000380688 CTR: c000000000186ac0^M
[    0.000000][    T0] REGS: c000000002867930 TRAP: 0700   Not tainted  (5.19.0-rc5-next-20220708-dirty)^M
[    0.000000][    T0] MSR:  8000000000022003 <SF,FP,RI,LE>  CR: 24282224  XER: 20040000^M
[    0.000000][    T0] CFAR: 0000000000000730 IRQMASK: 1 ^M
[    0.000000][    T0] GPR00: c000000000380688 c000000002867bd0 c000000002868d00 0000000000000065 ^M
[    0.000000][    T0] GPR04: 0000000000000001 0000000000000000 0000000000000080 000000000000000d ^M
[    0.000000][    T0] GPR08: 0000000000000000 0000000000000000 c0000000027fd000 000000000000000f ^M
[    0.000000][    T0] GPR12: c000000000186ac0 c000000002082280 0000000000000003 000000000000000d ^M
[    0.000000][    T0] GPR16: 0000000002cc00d0 0000000000000000 c000000002082280 0000000000000001 ^M
[    0.000000][    T0] GPR20: c000000002080942 0000000000000000 0000000000000000 0000000000000000 ^M
[    0.000000][    T0] GPR24: 0000000000000000 c0000000010d6168 0000000000000000 c0000000020034c8 ^M
[    0.000000][    T0] GPR28: 0000002800000000 0000000000000000 c000000002080942 c000000002953260 ^M
[    0.000000][    T0] NIP [c00000000038068c] static_key_enable_cpuslocked+0xfc/0x120^M
[    0.000000][    T0] LR [c000000000380688] static_key_enable_cpuslocked+0xf8/0x120^M
[    0.000000][    T0] Call Trace:^M
[    0.000000][    T0] [c000000002867bd0] [c000000000380688] static_key_enable_cpuslocked+0xf8/0x120 (unreliable)^M
[    0.000000][    T0] [c000000002867c40] [c000000000380810] static_key_enable+0x30/0x50^M
[    0.000000][    T0] [c000000002867c70] [c000000002030314] setup_forced_irqthreads+0x28/0x40^M
[    0.000000][    T0] [c000000002867c90] [c000000002003568] do_early_param+0xa0/0x108^M
[    0.000000][    T0] [c000000002867d10] [c000000000175340] parse_args+0x290/0x4e0^M
[    0.000000][    T0] [c000000002867e10] [c000000002003c74] parse_early_options+0x48/0x5c^M
[    0.000000][    T0] [c000000002867e30] [c000000002003ce0] parse_early_param+0x58/0x84^M
[    0.000000][    T0] [c000000002867e60] [c000000002009878] early_init_devtree+0xd4/0x518^M
[    0.000000][    T0] [c000000002867f10] [c00000000200aee0] early_setup+0xb4/0x214^M

After this fix, the WARN does not show again.

Kind Regards
Zhouyi
--
 arch/powerpc/kernel/prom.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 1066b072db35..bfe170ed6b12 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -751,7 +751,13 @@ void __init early_init_devtree(void *params)
 	early_init_dt_scan_root();
 	early_init_dt_scan_memory_ppc();
 
+	/*
+	 * As generic code authors expect to be able to use static keys
+	 * in early_param() handlers, we initialize the static keys just
+	 * before parsing early params (it's fine to call jump_label_init
+	 * more than once).
+	 */
+	jump_label_init();
 	parse_early_param();
 
 	/* make sure we've parsed cmdline for mem= before this */
-- 
2.25.1