---

yaml
---
r: 140963
b: refs/heads/master
c: 5be71b6
h: refs/heads/master
i:
  140961: eb9b5b6
  140959: 64f9771
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 6404434525bb9f8f2239998f30fd7c93f2efa5b3
+refs/heads/master: 5be71b61f17b0e3bc8ad0b1a1b7b53ab7d574ebb

trunk/kernel/trace/trace_syscalls.c

@@ -5,7 +5,11 @@
 #include "trace_output.h"
 #include "trace.h"
 
-static atomic_t refcount;
+/* Keep a counter of the syscall tracing users */
+static int refcount;
+
+/* Prevent from races on thread flags toggling */
+static DEFINE_MUTEX(syscall_trace_lock);
 
 /* Option to display the parameters types */
 enum {
@@ -96,9 +100,11 @@ void start_ftrace_syscalls(void)
 	unsigned long flags;
 	struct task_struct *g, *t;
 
+	mutex_lock(&syscall_trace_lock);
+
 	/* Don't enable the flag on the tasks twice */
-	if (atomic_inc_return(&refcount) != 1)
-		return;
+	if (++refcount != 1)
+		goto unlock;
 
 	arch_init_ftrace_syscalls();
 	read_lock_irqsave(&tasklist_lock, flags);
@@ -108,16 +114,21 @@ void start_ftrace_syscalls(void)
 	} while_each_thread(g, t);
 
 	read_unlock_irqrestore(&tasklist_lock, flags);
+
+unlock:
+	mutex_unlock(&syscall_trace_lock);
 }
 
 void stop_ftrace_syscalls(void)
 {
 	unsigned long flags;
 	struct task_struct *g, *t;
 
+	mutex_lock(&syscall_trace_lock);
+
 	/* There are perhaps still some users */
-	if (atomic_dec_return(&refcount))
-		return;
+	if (--refcount)
+		goto unlock;
 
 	read_lock_irqsave(&tasklist_lock, flags);
 
@@ -126,6 +137,9 @@ void stop_ftrace_syscalls(void)
 	} while_each_thread(g, t);
 
 	read_unlock_irqrestore(&tasklist_lock, flags);
+
+unlock:
+	mutex_unlock(&syscall_trace_lock);
 }
 
 void ftrace_syscall_enter(struct pt_regs *regs)