tracing: Replace the per_cpu() with __this_cpu*() in trace_stack.c

The updates to the trace_active per cpu variable can be updated with the
__this_cpu_*() functions as it only gets updated on the CPU that the variable
is on.

Thanks to Paul McKenney for suggesting __this_cpu_* instead of this_cpu_*.

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 5fb1f2c87e6b846b7f9d32823ef3aede4b28db9e..338d076a06da8d0f65416ec1ef706b5714f739c4 100644 (file)
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -207,13 +207,12 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip,
                 struct ftrace_ops *op, struct pt_regs *pt_regs)
 {
        unsigned long stack;
-       int cpu;
 
        preempt_disable_notrace();
 
-       cpu = raw_smp_processor_id();
        /* no atomic needed, we only modify this variable by this cpu */
-       if (per_cpu(trace_active, cpu)++ != 0)
+       __this_cpu_inc(trace_active);
+       if (__this_cpu_read(trace_active) != 1)
                goto out;
 
        ip += MCOUNT_INSN_SIZE;
@@ -221,7 +220,7 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip,
        check_stack(ip, &stack);
 
  out:
-       per_cpu(trace_active, cpu)--;
+       __this_cpu_dec(trace_active);
        /* prevent recursion in schedule */
        preempt_enable_notrace();
 }
@@ -253,7 +252,6 @@ stack_max_size_write(struct file *filp, const char __user *ubuf,
        long *ptr = filp->private_data;
        unsigned long val, flags;
        int ret;
-       int cpu;
 
        ret = kstrtoul_from_user(ubuf, count, 10, &val);
        if (ret)
@@ -266,14 +264,13 @@ stack_max_size_write(struct file *filp, const char __user *ubuf,
         * we will cause circular lock, so we also need to increase
         * the percpu trace_active here.
         */
-       cpu = smp_processor_id();
-       per_cpu(trace_active, cpu)++;
+       __this_cpu_inc(trace_active);
 
        arch_spin_lock(&stack_trace_max_lock);
        *ptr = val;
        arch_spin_unlock(&stack_trace_max_lock);
 
-       per_cpu(trace_active, cpu)--;
+       __this_cpu_dec(trace_active);
        local_irq_restore(flags);
 
        return count;
@@ -307,12 +304,9 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
 
 static void *t_start(struct seq_file *m, loff_t *pos)
 {
-       int cpu;
-
        local_irq_disable();
 
-       cpu = smp_processor_id();
-       per_cpu(trace_active, cpu)++;
+       __this_cpu_inc(trace_active);
 
        arch_spin_lock(&stack_trace_max_lock);
 
@@ -324,12 +318,9 @@ static void *t_start(struct seq_file *m, loff_t *pos)
 
 static void t_stop(struct seq_file *m, void *p)
 {
-       int cpu;
-
        arch_spin_unlock(&stack_trace_max_lock);
 
-       cpu = smp_processor_id();
-       per_cpu(trace_active, cpu)--;
+       __this_cpu_dec(trace_active);
 
        local_irq_enable();
 }