[PATCH 2/2] ARM: Replace this_cpu_* with raw_cpu_* in panic_bad_stack()

[Zhen Lei]

The hardware automatically disable the IRQ interrupt before jumping to the
interrupt or exception vector. Therefore, the preempt_disable() operation
in this_cpu_read() after macro expansion is unnecessary. In fact, function
this_cpu_read() may trigger scheduling, see pseudocode below.

Pseudocode of this_cpu_read(xx):
preempt_disable_notrace();
raw_cpu_read(xx);
if (unlikely(__preempt_count_dec_and_test()))
	__preempt_schedule_notrace();

Therefore, use raw_cpu_* instead of this_cpu_* to eliminate potential
hazards. At the very least, it reduces a few lines of assembly code.

Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
KernelVersion: v6.0-rc2
 arch/arm/kernel/traps.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 1518a1f443ff866..d5903d790cf3b7e 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -927,9 +927,9 @@ asmlinkage void handle_bad_stack(struct pt_regs *regs)
 {
 	unsigned long tsk_stk = (unsigned long)current->stack;
 #ifdef CONFIG_IRQSTACKS
-	unsigned long irq_stk = (unsigned long)this_cpu_read(irq_stack_ptr);
+	unsigned long irq_stk = (unsigned long)raw_cpu_read(irq_stack_ptr);
 #endif
-	unsigned long ovf_stk = (unsigned long)this_cpu_read(overflow_stack_ptr);
+	unsigned long ovf_stk = (unsigned long)raw_cpu_read(overflow_stack_ptr);
 
 	console_verbose();
 	pr_emerg("Insufficient stack space to handle exception!");
-- 
2.25.1