From 29a2cff09e52ea9a7ecc4bef3e52012d1dd3d525 Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum@gmail.com>
Date: Fri, 16 May 2008 16:33:29 +0200
Subject: [PATCH] proc: add "stacktrace" file

This patch adds a /proc/<pid>/stacktrace file which will show the current
kernel stack trace of the specified pid.

Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
---
 fs/proc/base.c |   49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 808cbdc..9e2e29e 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -64,6 +64,7 @@
 #include <linux/mm.h>
 #include <linux/rcupdate.h>
 #include <linux/kallsyms.h>
+#include <linux/stacktrace.h>
 #include <linux/resource.h>
 #include <linux/module.h>
 #include <linux/mount.h>
@@ -318,6 +319,48 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer)
 }
 #endif /* CONFIG_KALLSYMS */
 
+#ifdef CONFIG_STACKTRACE
+static int proc_stack_trace(struct task_struct *task, char *buffer)
+{
+	char *cur;
+	unsigned int len;
+
+	struct stack_trace trace;
+	unsigned long entries[32];
+	int i;
+
+	cur = buffer;
+
+	trace.nr_entries = 0;
+	trace.entries = entries;
+	trace.max_entries = ARRAY_SIZE(entries);
+	trace.skip = 0;
+
+	save_stack_trace_tsk(task, &trace);
+
+	for(i = 0; i < trace.nr_entries; ++i) {
+		unsigned long ip = trace.entries[i];
+
+		len = sprintf(cur, "[<%p>] ", (void *) ip);
+		if (len < 0)
+			return len;
+		cur += len;
+
+		len = sprint_symbol(cur, ip);
+		if (len < 0)
+			return len;
+		cur += len;
+
+		len = sprintf(cur, "\n");
+		if (len < 0)
+			return len;
+		cur += len;
+	}
+
+	return cur - buffer;
+}
+#endif
+
 #ifdef CONFIG_SCHEDSTATS
 /*
  * Provides /proc/PID/schedstat
@@ -2425,6 +2468,9 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_KALLSYMS
 	INF("wchan",      S_IRUGO, pid_wchan),
 #endif
+#ifdef CONFIG_STACKTRACE
+	INF("stacktrace", S_IRUSR, stack_trace),
+#endif
 #ifdef CONFIG_SCHEDSTATS
 	INF("schedstat",  S_IRUGO, pid_schedstat),
 #endif
@@ -2757,6 +2803,9 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_KALLSYMS
 	INF("wchan",     S_IRUGO, pid_wchan),
 #endif
+#ifdef CONFIG_STACKTRACE
+	INF("stacktrace", S_IRUSR, stack_trace),
+#endif
 #ifdef CONFIG_SCHEDSTATS
 	INF("schedstat", S_IRUGO, pid_schedstat),
 #endif
-- 
1.5.4.1