Subject: printk: rename printk cpulock API and always disable interrupts
From: John Ogness <john.ogness@linutronix.de>
Date: Thu Jul 15 09:34:45 2021 +0206

From: John Ogness <john.ogness@linutronix.de>

The printk cpulock functions use local_irq_disable(). This means that
hardware interrupts are also disabled on PREEMPT_RT. To make this
clear, rename the functions to use the raw_ prefix:

raw_printk_cpu_lock_irqsave(flags);
raw_printk_cpu_unlock_irqrestore(flags);

Also, these functions were a NOP for !CONFIG_SMP. But for !CONFIG_SMP
they still need to disable hardware interrupts. So modify them
appropriately for this.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 include/linux/printk.h |   30 ++++++++++++++----------------
 lib/dump_stack.c       |    4 ++--
 lib/nmi_backtrace.c    |    4 ++--
 3 files changed, 18 insertions(+), 20 deletions(-)
---
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -280,17 +280,22 @@ static inline void dump_stack(void)
 extern int __printk_cpu_trylock(void);
 extern void __printk_wait_on_cpu_lock(void);
 extern void __printk_cpu_unlock(void);
+#else
+#define __printk_cpu_trylock()		1
+#define __printk_wait_on_cpu_lock()
+#define __printk_cpu_unlock()
+#endif /* CONFIG_SMP */
 
 /**
- * printk_cpu_lock_irqsave() - Acquire the printk cpu-reentrant spinning
- *                             lock and disable interrupts.
+ * raw_printk_cpu_lock_irqsave() - Acquire the printk cpu-reentrant spinning
+ *                                 lock and disable interrupts.
  * @flags: Stack-allocated storage for saving local interrupt state,
- *         to be passed to printk_cpu_unlock_irqrestore().
+ *         to be passed to raw_printk_cpu_unlock_irqrestore().
  *
  * If the lock is owned by another CPU, spin until it becomes available.
  * Interrupts are restored while spinning.
  */
-#define printk_cpu_lock_irqsave(flags)		\
+#define raw_printk_cpu_lock_irqsave(flags)	\
 	for (;;) {				\
 		local_irq_save(flags);		\
 		if (__printk_cpu_trylock())	\
@@ -300,22 +305,15 @@ extern void __printk_cpu_unlock(void);
 	}
 
 /**
- * printk_cpu_unlock_irqrestore() - Release the printk cpu-reentrant spinning
- *                                  lock and restore interrupts.
- * @flags: Caller's saved interrupt state, from printk_cpu_lock_irqsave().
+ * raw_printk_cpu_unlock_irqrestore() - Release the printk cpu-reentrant
+ *                                      spinning lock and restore interrupts.
+ * @flags: Caller's saved interrupt state from raw_printk_cpu_lock_irqsave().
  */
-#define printk_cpu_unlock_irqrestore(flags)	\
+#define raw_printk_cpu_unlock_irqrestore(flags)	\
 	do {					\
 		__printk_cpu_unlock();		\
 		local_irq_restore(flags);	\
-	} while (0)				\
-
-#else
-
-#define printk_cpu_lock_irqsave(flags) ((void)flags)
-#define printk_cpu_unlock_irqrestore(flags) ((void)flags)
-
-#endif /* CONFIG_SMP */
+	} while (0)
 
 extern int kptr_restrict;
 
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -102,9 +102,9 @@ asmlinkage __visible void dump_stack_lvl
 	 * Permit this cpu to perform nested stack dumps while serialising
 	 * against other CPUs
 	 */
-	printk_cpu_lock_irqsave(flags);
+	raw_printk_cpu_lock_irqsave(flags);
 	__dump_stack(log_lvl);
-	printk_cpu_unlock_irqrestore(flags);
+	raw_printk_cpu_unlock_irqrestore(flags);
 }
 EXPORT_SYMBOL(dump_stack_lvl);
 
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -93,7 +93,7 @@ bool nmi_cpu_backtrace(struct pt_regs *r
 		 * Allow nested NMI backtraces while serializing
 		 * against other CPUs.
 		 */
-		printk_cpu_lock_irqsave(flags);
+		raw_printk_cpu_lock_irqsave(flags);
 		if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
 			pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
 				cpu, (void *)instruction_pointer(regs));
@@ -104,7 +104,7 @@ bool nmi_cpu_backtrace(struct pt_regs *r
 			else
 				dump_stack();
 		}
-		printk_cpu_unlock_irqrestore(flags);
+		raw_printk_cpu_unlock_irqrestore(flags);
 		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
 		return true;
 	}