ftrace,kdb: Extend kdb to be able to dump the ftrace buffer

Add in a helper function to allow the kdb shell to dump the ftrace
buffer.

Modify trace.c to expose the capability to iterate over the ftrace
buffer in a read only capacity.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
CC: Frederic Weisbecker <fweisbec@gmail.com>

4 files changed, 163 insertions, 21 deletions

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index ffb1a5b0550e..4215530b490b 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -57,5 +57,8 @@ obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
 obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
 obj-$(CONFIG_KSYM_TRACER) += trace_ksym.o
 obj-$(CONFIG_EVENT_TRACING) += power-traces.o
+ifeq ($(CONFIG_TRACING),y)
+obj-$(CONFIG_KGDB_KDB) += trace_kdb.o
+endif
 
 libftrace-y := ftrace.o
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 086d36316805..d6736b93dc2a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -101,10 +101,7 @@ static inline void ftrace_enable_cpu(void)
         preempt_enable();
 }
 
-static cpumask_var_t __read_mostly      tracing_buffer_mask;
-
-#define for_each_tracing_cpu(cpu)       \
-        for_each_cpu(cpu, tracing_buffer_mask)
+cpumask_var_t __read_mostly     tracing_buffer_mask;
 
 /*
  * ftrace_dump_on_oops - variable to dump ftrace buffer on oops
@@ -1539,11 +1536,6 @@ int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
 }
 EXPORT_SYMBOL_GPL(trace_vprintk);
 
-enum trace_file_type {
-        TRACE_FILE_LAT_FMT      = 1,
-        TRACE_FILE_ANNOTATE     = 2,
-};
-
 static void trace_iterator_increment(struct trace_iterator *iter)
 {
         /* Don't allow ftrace to trace into the ring buffers */
@@ -1641,7 +1633,7 @@ struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
 }
 
 /* Find the next real entry, and increment the iterator to the next entry */
-static void *find_next_entry_inc(struct trace_iterator *iter)
+void *trace_find_next_entry_inc(struct trace_iterator *iter)
 {
         iter->ent = __find_next_entry(iter, &iter->cpu,
                                       &iter->lost_events, &iter->ts);
@@ -1676,19 +1668,19 @@ static void *s_next(struct seq_file *m, void *v, loff_t *pos)
                 return NULL;
 
         if (iter->idx < 0)
-                ent = find_next_entry_inc(iter);
+                ent = trace_find_next_entry_inc(iter);
         else
                 ent = iter;
 
         while (ent && iter->idx < i)
-                ent = find_next_entry_inc(iter);
+                ent = trace_find_next_entry_inc(iter);
 
         iter->pos = *pos;
 
         return ent;
 }
 
-static void tracing_iter_reset(struct trace_iterator *iter, int cpu)
+void tracing_iter_reset(struct trace_iterator *iter, int cpu)
 {
         struct trace_array *tr = iter->tr;
         struct ring_buffer_event *event;
@@ -2049,7 +2041,7 @@ int trace_empty(struct trace_iterator *iter)
 }
 
 /*  Called with trace_event_read_lock() held. */
-static enum print_line_t print_trace_line(struct trace_iterator *iter)
+enum print_line_t print_trace_line(struct trace_iterator *iter)
 {
         enum print_line_t ret;
 
@@ -3211,7 +3203,7 @@ waitagain:
 
         trace_event_read_lock();
         trace_access_lock(iter->cpu_file);
-        while (find_next_entry_inc(iter) != NULL) {
+        while (trace_find_next_entry_inc(iter) != NULL) {
                 enum print_line_t ret;
                 int len = iter->seq.len;
 
@@ -3294,7 +3286,7 @@ tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
                 if (ret != TRACE_TYPE_NO_CONSUME)
                         trace_consume(iter);
                 rem -= count;
-                if (!find_next_entry_inc(iter)) {
+                if (!trace_find_next_entry_inc(iter))   {
                         rem = 0;
                         iter->ent = NULL;
                         break;
@@ -3350,7 +3342,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
         if (ret <= 0)
                 goto out_err;
 
-        if (!iter->ent && !find_next_entry_inc(iter)) {
+        if (!iter->ent && !trace_find_next_entry_inc(iter)) {
                 ret = -EFAULT;
                 goto out_err;
         }
@@ -4414,7 +4406,7 @@ static struct notifier_block trace_die_notifier = {
  */
 #define KERN_TRACE              KERN_EMERG
 
-static void
+void
 trace_printk_seq(struct trace_seq *s)
 {
         /* Probably should print a warning here. */
@@ -4429,6 +4421,13 @@ trace_printk_seq(struct trace_seq *s)
         trace_seq_init(s);
 }
 
+void trace_init_global_iter(struct trace_iterator *iter)
+{
+        iter->tr = &global_trace;
+        iter->trace = current_trace;
+        iter->cpu_file = TRACE_PIPE_ALL_CPU;
+}
+
 static void
 __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
 {
@@ -4454,8 +4453,10 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
         if (disable_tracing)
                 ftrace_kill();
 
+        trace_init_global_iter(&iter);
+
         for_each_tracing_cpu(cpu) {
-                atomic_inc(&global_trace.data[cpu]->disabled);
+                atomic_inc(&iter.tr->data[cpu]->disabled);
         }
 
         old_userobj = trace_flags & TRACE_ITER_SYM_USEROBJ;
@@ -4504,7 +4505,7 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
                 iter.iter_flags |= TRACE_FILE_LAT_FMT;
                 iter.pos = -1;
 
-                if (find_next_entry_inc(&iter) != NULL) {
+                if (trace_find_next_entry_inc(&iter) != NULL) {
                         int ret;
 
                         ret = print_trace_line(&iter);
@@ -4526,7 +4527,7 @@ __ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
                 trace_flags |= old_userobj;
 
                 for_each_tracing_cpu(cpu) {
-                        atomic_dec(&global_trace.data[cpu]->disabled);
+                        atomic_dec(&iter.tr->data[cpu]->disabled);
                 }
                 tracing_on();
         }
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 2cd96399463f..0605fc00c176 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -338,6 +338,14 @@ struct trace_entry *tracing_get_trace_entry(struct trace_array *tr,
 struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
                                           int *ent_cpu, u64 *ent_ts);
 
+int trace_empty(struct trace_iterator *iter);
+
+void *trace_find_next_entry_inc(struct trace_iterator *iter);
+
+void trace_init_global_iter(struct trace_iterator *iter);
+
+void tracing_iter_reset(struct trace_iterator *iter, int cpu);
+
 void default_wait_pipe(struct trace_iterator *iter);
 void poll_wait_pipe(struct trace_iterator *iter);
 
@@ -380,6 +388,15 @@ void tracing_start_sched_switch_record(void);
 int register_tracer(struct tracer *type);
 void unregister_tracer(struct tracer *type);
 int is_tracing_stopped(void);
+enum trace_file_type {
+        TRACE_FILE_LAT_FMT      = 1,
+        TRACE_FILE_ANNOTATE     = 2,
+};
+
+extern cpumask_var_t __read_mostly tracing_buffer_mask;
+
+#define for_each_tracing_cpu(cpu)       \
+        for_each_cpu(cpu, tracing_buffer_mask)
 
 extern int process_new_ksym_entry(char *ksymname, int op, unsigned long addr);
 
@@ -471,6 +488,8 @@ trace_array_vprintk(struct trace_array *tr,
                     unsigned long ip, const char *fmt, va_list args);
 int trace_array_printk(struct trace_array *tr,
                        unsigned long ip, const char *fmt, ...);
+void trace_printk_seq(struct trace_seq *s);
+enum print_line_t print_trace_line(struct trace_iterator *iter);
 
 extern unsigned long trace_flags;
 
diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
new file mode 100644
index 000000000000..44cbda25b0a5
--- /dev/null
+++ b/kernel/trace/trace_kdb.c
@@ -0,0 +1,119 @@
+/*
+ * kdb helper for dumping the ftrace buffer
+ *
+ * Copyright (C) 2010 Jason Wessel <jason.wessel@windriver.com>
+ *
+ * ftrace_dump_buf based on ftrace_dump:
+ * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
+ * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
+ *
+ */
+#include <linux/init.h>
+#include <linux/kgdb.h>
+#include <linux/kdb.h>
+#include <linux/ftrace.h>
+
+#include "../debug/kdb/kdb_private.h"
+#include "trace.h"
+#include "trace_output.h"
+
+static void ftrace_dump_buf(int skip_lines)
+{
+        /* use static because iter can be a bit big for the stack */
+        static struct trace_iterator iter;
+        unsigned int old_userobj;
+        int cnt = 0, cpu;
+
+        trace_init_global_iter(&iter);
+
+        for_each_tracing_cpu(cpu) {
+                atomic_inc(&iter.tr->data[cpu]->disabled);
+        }
+
+        old_userobj = trace_flags;
+
+        /* don't look at user memory in panic mode */
+        trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
+
+        kdb_printf("Dumping ftrace buffer:\n");
+
+        /* reset all but tr, trace, and overruns */
+        memset(&iter.seq, 0,
+                   sizeof(struct trace_iterator) -
+                   offsetof(struct trace_iterator, seq));
+        iter.iter_flags |= TRACE_FILE_LAT_FMT;
+        iter.pos = -1;
+
+        for_each_tracing_cpu(cpu) {
+                iter.buffer_iter[cpu] =
+                        ring_buffer_read_prepare(iter.tr->buffer, cpu);
+                ring_buffer_read_start(iter.buffer_iter[cpu]);
+                tracing_iter_reset(&iter, cpu);
+        }
+
+        if (!trace_empty(&iter))
+                trace_find_next_entry_inc(&iter);
+        while (!trace_empty(&iter)) {
+                if (!cnt)
+                        kdb_printf("---------------------------------\n");
+                cnt++;
+
+                if (trace_find_next_entry_inc(&iter) != NULL && !skip_lines)
+                        print_trace_line(&iter);
+                if (!skip_lines)
+                        trace_printk_seq(&iter.seq);
+                else
+                        skip_lines--;
+                if (KDB_FLAG(CMD_INTERRUPT))
+                        goto out;
+        }
+
+        if (!cnt)
+                kdb_printf("   (ftrace buffer empty)\n");
+        else
+                kdb_printf("---------------------------------\n");
+
+out:
+        trace_flags = old_userobj;
+
+        for_each_tracing_cpu(cpu) {
+                atomic_dec(&iter.tr->data[cpu]->disabled);
+        }
+
+        for_each_tracing_cpu(cpu)
+                if (iter.buffer_iter[cpu])
+                        ring_buffer_read_finish(iter.buffer_iter[cpu]);
+}
+
+/*
+ * kdb_ftdump - Dump the ftrace log buffer
+ */
+static int kdb_ftdump(int argc, const char **argv)
+{
+        int skip_lines = 0;
+        char *cp;
+
+        if (argc > 1)
+                return KDB_ARGCOUNT;
+
+        if (argc) {
+                skip_lines = simple_strtol(argv[1], &cp, 0);
+                if (*cp)
+                        skip_lines = 0;
+        }
+
+        kdb_trap_printk++;
+        ftrace_dump_buf(skip_lines);
+        kdb_trap_printk--;
+
+        return 0;
+}
+
+static __init int kdb_ftrace_register(void)
+{
+        kdb_register_repeat("ftdump", kdb_ftdump, "", "Dump ftrace log",
+                            0, KDB_REPEAT_NONE);
+        return 0;
+}
+
+late_initcall(kdb_ftrace_register);