1 files changed, 84 insertions, 0 deletions
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
new file mode 100644
index 000000000000..32a28f563b13
--- /dev/null
+++ b/kernel/printk/printk_safe.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * printk_safe.c - Safe printk for printk-deadlock-prone contexts
+ */
+
+#include <linux/preempt.h>
+#include <linux/kdb.h>
+#include <linux/smp.h>
+#include <linux/cpumask.h>
+#include <linux/printk.h>
+#include <linux/kprobes.h>
+
+#include "internal.h"
+
+/* Context where printk messages are never suppressed */
+static atomic_t force_con;
+
+void printk_force_console_enter(void)
+{
+	atomic_inc(&force_con);
+}
+
+void printk_force_console_exit(void)
+{
+	atomic_dec(&force_con);
+}
+
+bool is_printk_force_console(void)
+{
+	return atomic_read(&force_con);
+}
+
+static DEFINE_PER_CPU(int, printk_context);
+
+/* Can be preempted by NMI. */
+void __printk_safe_enter(void)
+{
+	this_cpu_inc(printk_context);
+}
+
+/* Can be preempted by NMI. */
+void __printk_safe_exit(void)
+{
+	this_cpu_dec(printk_context);
+}
+
+void __printk_deferred_enter(void)
+{
+	cant_migrate();
+	__printk_safe_enter();
+}
+
+void __printk_deferred_exit(void)
+{
+	cant_migrate();
+	__printk_safe_exit();
+}
+
+bool is_printk_legacy_deferred(void)
+{
+	/*
+	 * The per-CPU variable @printk_context can be read safely in any
+	 * context. CPU migration is always disabled when set.
+	 *
+	 * A context holding the printk_cpu_sync must not spin waiting for
+	 * another CPU. For legacy printing, it could be the console_lock
+	 * or the port lock.
+	 */
+	return (force_legacy_kthread() ||
+		this_cpu_read(printk_context) ||
+		in_nmi() ||
+		is_printk_cpu_sync_owner());
+}
+
+asmlinkage int vprintk(const char *fmt, va_list args)
+{
+#ifdef CONFIG_KGDB_KDB
+	/* Allow to pass printk() to kdb but avoid a recursion. */
+	if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
+		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
+#endif
+	return vprintk_default(fmt, args);
+}
+EXPORT_SYMBOL(vprintk);