[PATCH printk v1 02/10] printk: rename printk cpulock API and always disable interrupts

John Ogness
2021-08-03T13:13:32Z

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>
---
include/linux/printk.h | 30 ++++++++++++++----------------
lib/dump_stack.c | 4 ++--
lib/nmi_backtrace.c | 4 ++--
3 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 259af4f97f50..ac738d1d9934 100644
--- 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;

diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index cd3387bb34e5..7af32829b062 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -101,9 +101,9 @@ asmlinkage __visible void dump_stack_lvl(const char *log_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);

diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index f9e89001b52e..569ec8676072 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -93,7 +93,7 @@ bool nmi_cpu_backtrace(struct pt_regs *regs)
* 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 *regs)
else
dump_stack();
}
- printk_cpu_unlock_irqrestore(flags);
+ raw_printk_cpu_unlock_irqrestore(flags);
cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
return true;
}
--
2.20.1