3 files changed, 34 insertions, 9 deletions
diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index a3aa63e47637..ba2e85a0ff5b 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -134,4 +134,7 @@ extern phys_addr_t per_cpu_ptr_to_phys(void *addr);
        (typeof(type) __percpu *)__alloc_percpu(sizeof(type),           \
                                                __alignof__(type))
+/* To avoid include hell, as printk can not declare this, we declare it here */
+DECLARE_PER_CPU(printk_func_t, printk_func);
 #endif /* __LINUX_PERCPU_H */
diff --git a/include/linux/printk.h b/include/linux/printk.h
index d78125f73ac4..3bbd979d32fb 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -162,6 +162,8 @@ extern int kptr_restrict;
 extern void wake_up_klogd(void);
+typedef int(*printk_func_t)(const char *fmt, va_list args);
 void log_buf_kexec_setup(void);
 void __init setup_log_buf(int early);
 void dump_stack_set_arch_desc(const char *fmt, ...);
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ced2b84b1cb7..f7b723f98cb9 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1807,6 +1807,30 @@ asmlinkage int printk_emit(int facility, int level,
 }
 EXPORT_SYMBOL(printk_emit);
+int vprintk_default(const char *fmt, va_list args)
+{
+        int r;
+#ifdef CONFIG_KGDB_KDB
+        if (unlikely(kdb_trap_printk)) {
+                r = vkdb_printf(fmt, args);
+                return r;
+        }
+#endif
+        r = vprintk_emit(0, -1, NULL, 0, fmt, args);
+        return r;
+}
+EXPORT_SYMBOL_GPL(vprintk_default);
+/*
+ * This allows printk to be diverted to another function per cpu.
+ * This is useful for calling printk functions from within NMI
+ * without worrying about race conditions that can lock up the
+ * box.
+ */
+DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default;
 /**
 * printk - print a kernel message
 * @fmt: format string
@@ -1830,19 +1854,15 @@ EXPORT_SYMBOL(printk_emit);
 */
 asmlinkage __visible int printk(const char *fmt, ...)
 {
+        printk_func_t vprintk_func;
        va_list args;
        int r;
-#ifdef CONFIG_KGDB_KDB
-        if (unlikely(kdb_trap_printk)) {
-                va_start(args, fmt);
-                r = vkdb_printf(fmt, args);
-                va_end(args);
-                return r;
-        }
-#endif
        va_start(args, fmt);
-        r = vprintk_emit(0, -1, NULL, 0, fmt, args);
+        preempt_disable();
+        vprintk_func = this_cpu_read(printk_func);
+        r = vprintk_func(fmt, args);
+        preempt_enable();
        va_end(args);
        return r;