tracing: tracepoints for softirq entry/exit - add softirq-to-name array

Create a 'softirq_to_name' array, which is indexed by softirq #, so
that we can easily convert between the softirq index # and its name, in
order to get more meaningful output messages.

LKML-Reference: <20090312183336.GB3352@redhat.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>

include/linux/interrupt.h

@@ -258,6 +258,11 @@ enum
 	NR_SOFTIRQS
 };
 
+/* map softirq index to softirq name. update 'softirq_to_name' in
+ * kernel/softirq.c when adding a new softirq.
+ */
+extern char *softirq_to_name[NR_SOFTIRQS];
+
 /* softirq mask and active fields moved to irq_cpustat_t in
  * asm/hardirq.h to get better cache usage.  KAO
  */

kernel/softirq.c

@@ -53,6 +53,12 @@ static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp
 
 static DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
 
+char *softirq_to_name[NR_SOFTIRQS] = {
+	"HI_SOFTIRQ", "TIMER_SOFTIRQ", "NET_TX_SOFTIRQ", "NET_RX_SOFTIRQ",
+	"BLOCK_SOFTIRQ", "TASKLET_SOFTIRQ", "SCHED_SOFTIRQ", "HRTIMER_SOFTIRQ",
+	"RCU_SOFTIRQ"
+};
+
 /*
  * we cannot loop indefinitely here to avoid userspace starvation,
  * but we also don't want to introduce a worst case 1/HZ latency
@@ -209,9 +215,10 @@ restart:
 			h->action(h);
 
 			if (unlikely(prev_count != preempt_count())) {
-				printk(KERN_ERR "huh, entered softirq %td %p"
+				printk(KERN_ERR "huh, entered softirq %td %s %p"
 				       "with preempt_count %08x,"
 				       " exited with %08x?\n", h - softirq_vec,
+				       softirq_to_name[h - softirq_vec],
 				       h->action, prev_count, preempt_count());
 				preempt_count() = prev_count;
 			}