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, 57 insertions, 0 deletions

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index a03e7f6d90c3..b15153060417 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -6,6 +6,7 @@
 #include <linux/sched.h>
 #include <linux/stacktrace.h>
 #include <linux/module.h>
+#include <linux/uaccess.h>
 #include <asm/stacktrace.h>
 
 static void save_stack_warning(void *data, char *msg)
@@ -83,3 +84,59 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
                 trace->entries[trace->nr_entries++] = ULONG_MAX;
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
+
+/* Userspace stacktrace - based on kernel/trace/trace_sysprof.c */
+
+struct stack_frame {
+        const void __user       *next_fp;
+        unsigned long           return_address;
+};
+
+static int copy_stack_frame(const void __user *fp, struct stack_frame *frame)
+{
+        int ret;
+
+        if (!access_ok(VERIFY_READ, fp, sizeof(*frame)))
+                return 0;
+
+        ret = 1;
+        pagefault_disable();
+        if (__copy_from_user_inatomic(frame, fp, sizeof(*frame)))
+                ret = 0;
+        pagefault_enable();
+
+        return ret;
+}
+
+void save_stack_trace_user(struct stack_trace *trace)
+{
+        /*
+         * Trace user stack if we are not a kernel thread
+         */
+        if (current->mm) {
+                const struct pt_regs *regs = task_pt_regs(current);
+                const void __user *fp = (const void __user *)regs->bp;
+
+                if (trace->nr_entries < trace->max_entries)
+                        trace->entries[trace->nr_entries++] = regs->ip;
+
+                while (trace->nr_entries < trace->max_entries) {
+                        struct stack_frame frame;
+                        frame.next_fp = NULL;
+                        frame.return_address = 0;
+                        if (!copy_stack_frame(fp, &frame))
+                                break;
+                        if ((unsigned long)fp < regs->sp)
+                                break;
+                        if (frame.return_address)
+                                trace->entries[trace->nr_entries++] =
+                                        frame.return_address;
+                        if (fp == frame.next_fp)
+                                break;
+                        fp = frame.next_fp;
+                }
+        }
+        if (trace->nr_entries < trace->max_entries)
+                trace->entries[trace->nr_entries++] = ULONG_MAX;
+}
+