tracing: add support for userspace stacktraces in tracing/iter_ctrl

Impact: add new (default-off) tracing visualization feature

Usage example:

 mount -t debugfs nodev /sys/kernel/debug
 cd /sys/kernel/debug/tracing
 echo userstacktrace >iter_ctrl
 echo sched_switch >current_tracer
 echo 1 >tracing_enabled
 .... run application ...
 echo 0 >tracing_enabled

Then read one of 'trace','latency_trace','trace_pipe'.

To get the best output you can compile your userspace programs with
frame pointers (at least glibc + the app you are tracing).

Signed-off-by: Török Edwin <edwintorok@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 93 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4ee6f0375222..ced8b4fa9f51 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -275,6 +275,7 @@ static const char *trace_options[] = {
         "ftrace_preempt",
         "branch",
         "annotate",
+        "userstacktrace",
         NULL
 };
 
@@ -918,6 +919,44 @@ void __trace_stack(struct trace_array *tr,
         ftrace_trace_stack(tr, data, flags, skip, preempt_count());
 }
 
+static void ftrace_trace_userstack(struct trace_array *tr,
+                   struct trace_array_cpu *data,
+                   unsigned long flags, int pc)
+{
+        struct userstack_entry *entry;
+        struct stack_trace trace;
+        struct ring_buffer_event *event;
+        unsigned long irq_flags;
+
+        if (!(trace_flags & TRACE_ITER_USERSTACKTRACE))
+                return;
+
+        event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry),
+                                         &irq_flags);
+        if (!event)
+                return;
+        entry   = ring_buffer_event_data(event);
+        tracing_generic_entry_update(&entry->ent, flags, pc);
+        entry->ent.type         = TRACE_USER_STACK;
+
+        memset(&entry->caller, 0, sizeof(entry->caller));
+
+        trace.nr_entries        = 0;
+        trace.max_entries       = FTRACE_STACK_ENTRIES;
+        trace.skip              = 0;
+        trace.entries           = entry->caller;
+
+        save_stack_trace_user(&trace);
+        ring_buffer_unlock_commit(tr->buffer, event, irq_flags);
+}
+
+void __trace_userstack(struct trace_array *tr,
+                   struct trace_array_cpu *data,
+                   unsigned long flags)
+{
+        ftrace_trace_userstack(tr, data, flags, preempt_count());
+}
+
 static void
 ftrace_trace_special(void *__tr, void *__data,
                      unsigned long arg1, unsigned long arg2, unsigned long arg3,
@@ -941,6 +980,7 @@ ftrace_trace_special(void *__tr, void *__data,
         entry->arg3                     = arg3;
         ring_buffer_unlock_commit(tr->buffer, event, irq_flags);
         ftrace_trace_stack(tr, data, irq_flags, 4, pc);
+        ftrace_trace_userstack(tr, data, irq_flags, pc);
 
         trace_wake_up();
 }
@@ -979,6 +1019,7 @@ tracing_sched_switch_trace(struct trace_array *tr,
         entry->next_cpu = task_cpu(next);
         ring_buffer_unlock_commit(tr->buffer, event, irq_flags);
         ftrace_trace_stack(tr, data, flags, 5, pc);
+        ftrace_trace_userstack(tr, data, flags, pc);
 }
 
 void
@@ -1008,6 +1049,7 @@ tracing_sched_wakeup_trace(struct trace_array *tr,
         entry->next_cpu                 = task_cpu(wakee);
         ring_buffer_unlock_commit(tr->buffer, event, irq_flags);
         ftrace_trace_stack(tr, data, flags, 6, pc);
+        ftrace_trace_userstack(tr, data, flags, pc);
 
         trace_wake_up();
 }
@@ -1387,6 +1429,31 @@ seq_print_ip_sym(struct trace_seq *s, unsigned long ip, unsigned long sym_flags)
         return ret;
 }
 
+static int
+seq_print_userip_objs(const struct userstack_entry *entry, struct trace_seq *s,
+                unsigned long sym_flags)
+{
+        int ret = 1;
+        unsigned i;
+
+        for (i = 0; i < FTRACE_STACK_ENTRIES; i++) {
+                unsigned long ip = entry->caller[i];
+
+                if (ip == ULONG_MAX || !ret)
+                        break;
+                if (i)
+                        ret = trace_seq_puts(s, " <- ");
+                if (!ip) {
+                        ret = trace_seq_puts(s, "??");
+                        continue;
+                }
+                if (ret /*&& (sym_flags & TRACE_ITER_SYM_ADDR)*/)
+                        ret = trace_seq_printf(s, " <" IP_FMT ">", ip);
+        }
+
+        return ret;
+}
+
 static void print_lat_help_header(struct seq_file *m)
 {
         seq_puts(m, "#                  _------=> CPU#            \n");
@@ -1702,6 +1769,16 @@ print_lat_fmt(struct trace_iterator *iter, unsigned int trace_idx, int cpu)
                                  field->line);
                 break;
         }
+        case TRACE_USER_STACK: {
+                struct userstack_entry *field;
+
+                trace_assign_type(field, entry);
+
+                seq_print_userip_objs(field, s, sym_flags);
+                if (entry->flags & TRACE_FLAG_CONT)
+                        trace_seq_print_cont(s, iter);
+                break;
+        }
         default:
                 trace_seq_printf(s, "Unknown type %d\n", entry->type);
         }
@@ -1853,6 +1930,19 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
                                  field->line);
                 break;
         }
+        case TRACE_USER_STACK: {
+                struct userstack_entry *field;
+
+                trace_assign_type(field, entry);
+
+                ret = seq_print_userip_objs(field, s, sym_flags);
+                if (!ret)
+                        return TRACE_TYPE_PARTIAL_LINE;
+                ret = trace_seq_putc(s, '\n');
+                if (!ret)
+                        return TRACE_TYPE_PARTIAL_LINE;
+                break;
+        }
         }
         return TRACE_TYPE_HANDLED;
 }
@@ -1912,6 +2002,7 @@ static enum print_line_t print_raw_fmt(struct trace_iterator *iter)
                 break;
         }
         case TRACE_SPECIAL:
+        case TRACE_USER_STACK:
         case TRACE_STACK: {
                 struct special_entry *field;
 
@@ -2000,6 +2091,7 @@ static enum print_line_t print_hex_fmt(struct trace_iterator *iter)
                 break;
         }
         case TRACE_SPECIAL:
+        case TRACE_USER_STACK:
         case TRACE_STACK: {
                 struct special_entry *field;
 
@@ -2054,6 +2146,7 @@ static enum print_line_t print_bin_fmt(struct trace_iterator *iter)
                 break;
         }
         case TRACE_SPECIAL:
+        case TRACE_USER_STACK:
         case TRACE_STACK: {
                 struct special_entry *field;