1 files changed, 13 insertions, 24 deletions

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 98c9011eac78..e74be38245ad 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -30,6 +30,7 @@
 char kdb_prompt_str[CMD_BUFLEN];
 
 int kdb_trap_printk;
+int kdb_printf_cpu = -1;
 
 static int kgdb_transition_check(char *buffer)
 {
@@ -554,31 +555,26 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
 	int linecount;
 	int colcount;
 	int logging, saved_loglevel = 0;
-	int saved_trap_printk;
-	int got_printf_lock = 0;
 	int retlen = 0;
 	int fnd, len;
+	int this_cpu, old_cpu;
 	char *cp, *cp2, *cphold = NULL, replaced_byte = ' ';
 	char *moreprompt = "more> ";
 	struct console *c = console_drivers;
-	static DEFINE_SPINLOCK(kdb_printf_lock);
 	unsigned long uninitialized_var(flags);
 
-	preempt_disable();
-	saved_trap_printk = kdb_trap_printk;
-	kdb_trap_printk = 0;
-
 	/* Serialize kdb_printf if multiple cpus try to write at once.
 	 * But if any cpu goes recursive in kdb, just print the output,
 	 * even if it is interleaved with any other text.
 	 */
-	if (!KDB_STATE(PRINTF_LOCK)) {
-		KDB_STATE_SET(PRINTF_LOCK);
-		spin_lock_irqsave(&kdb_printf_lock, flags);
-		got_printf_lock = 1;
-		atomic_inc(&kdb_event);
-	} else {
-		__acquire(kdb_printf_lock);
+	local_irq_save(flags);
+	this_cpu = smp_processor_id();
+	for (;;) {
+		old_cpu = cmpxchg(&kdb_printf_cpu, -1, this_cpu);
+		if (old_cpu == -1 || old_cpu == this_cpu)
+			break;
+
+		cpu_relax();
 	}
 
 	diag = kdbgetintenv("LINES", &linecount);
@@ -847,16 +843,9 @@ kdb_print_out:
 	suspend_grep = 0; /* end of what may have been a recursive call */
 	if (logging)
 		console_loglevel = saved_loglevel;
-	if (KDB_STATE(PRINTF_LOCK) && got_printf_lock) {
-		got_printf_lock = 0;
-		spin_unlock_irqrestore(&kdb_printf_lock, flags);
-		KDB_STATE_CLEAR(PRINTF_LOCK);
-		atomic_dec(&kdb_event);
-	} else {
-		__release(kdb_printf_lock);
-	}
-	kdb_trap_printk = saved_trap_printk;
-	preempt_enable();
+	/* kdb_printf_cpu locked the code above. */
+	smp_store_release(&kdb_printf_cpu, old_cpu);
+	local_irq_restore(flags);
 	return retlen;
 }