proc: add /proc/*/stack

/proc/*/stack adds the ability to query a task's stack trace. It is more
useful than /proc/*/wchan as it provides full stack trace instead of single
depth. Example output:

	$ cat /proc/self/stack
	[<c010a271>] save_stack_trace_tsk+0x17/0x35
	[<c01827b4>] proc_pid_stack+0x4a/0x76
	[<c018312d>] proc_single_show+0x4a/0x5e
	[<c016bdec>] seq_read+0xf3/0x29f
	[<c015a004>] vfs_read+0x6d/0x91
	[<c015a0c1>] sys_read+0x3b/0x60
	[<c0102eda>] syscall_call+0x7/0xb
	[<ffffffff>] 0xffffffff

[add save_stack_trace_tsk() on mips, ACK Ralf --adobriyan]
Signed-off-by: Ken Chen <kenchen@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

3 files changed, 57 insertions, 6 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 71df353e367c..334ef2f983fa 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -140,6 +140,7 @@ Table 1-1: Process specific entries in /proc
  statm          Process memory status information
  status         Process status in human readable form
  wchan          If CONFIG_KALLSYMS is set, a pre-decoded wchan
+ stack          Report full stack trace, enable via CONFIG_STACKTRACE
  smaps          Extension based on maps, the rss size for each mapped file
 ..............................................................................
 
diff --git a/arch/mips/kernel/stacktrace.c b/arch/mips/kernel/stacktrace.c
index 0632e2a849c0..58f5cd76c8c3 100644
--- a/arch/mips/kernel/stacktrace.c
+++ b/arch/mips/kernel/stacktrace.c
@@ -32,7 +32,8 @@ static void save_raw_context_stack(struct stack_trace *trace,
         }
 }
 
-static void save_context_stack(struct stack_trace *trace, struct pt_regs *regs)
+static void save_context_stack(struct stack_trace *trace,
+        struct task_struct *tsk, struct pt_regs *regs)
 {
         unsigned long sp = regs->regs[29];
 #ifdef CONFIG_KALLSYMS
@@ -41,7 +42,7 @@ static void save_context_stack(struct stack_trace *trace, struct pt_regs *regs)
 
         if (raw_show_trace || !__kernel_text_address(pc)) {
                 unsigned long stack_page =
-                        (unsigned long)task_stack_page(current);
+                        (unsigned long)task_stack_page(tsk);
                 if (stack_page && sp >= stack_page &&
                     sp <= stack_page + THREAD_SIZE - 32)
                         save_raw_context_stack(trace, sp);
@@ -54,7 +55,7 @@ static void save_context_stack(struct stack_trace *trace, struct pt_regs *regs)
                         trace->entries[trace->nr_entries++] = pc;
                 if (trace->nr_entries >= trace->max_entries)
                         break;
-                pc = unwind_stack(current, &sp, pc, &ra);
+                pc = unwind_stack(tsk, &sp, pc, &ra);
         } while (pc);
 #else
         save_raw_context_stack(trace, sp);
@@ -66,12 +67,23 @@ static void save_context_stack(struct stack_trace *trace, struct pt_regs *regs)
  */
 void save_stack_trace(struct stack_trace *trace)
 {
+        save_stack_trace_tsk(current, trace);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace);
+
+void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
+{
         struct pt_regs dummyregs;
         struct pt_regs *regs = &dummyregs;
 
         WARN_ON(trace->nr_entries || !trace->max_entries);
 
-        prepare_frametrace(regs);
-        save_context_stack(trace, regs);
+        if (tsk != current) {
+                regs->regs[29] = tsk->thread.reg29;
+                regs->regs[31] = 0;
+                regs->cp0_epc = tsk->thread.reg31;
+        } else
+                prepare_frametrace(regs);
+        save_context_stack(trace, tsk, regs);
 }
-EXPORT_SYMBOL_GPL(save_stack_trace);
+EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
diff --git a/fs/proc/base.c b/fs/proc/base.c
index ce7a6da1b6a0..eb7b4654d6aa 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -65,6 +65,7 @@
 #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>
@@ -337,6 +338,37 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer)
 }
 #endif /* CONFIG_KALLSYMS */
 
+#ifdef CONFIG_STACKTRACE
+
+#define MAX_STACK_TRACE_DEPTH   64
+
+static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
+                          struct pid *pid, struct task_struct *task)
+{
+        struct stack_trace trace;
+        unsigned long *entries;
+        int i;
+
+        entries = kmalloc(MAX_STACK_TRACE_DEPTH * sizeof(*entries), GFP_KERNEL);
+        if (!entries)
+                return -ENOMEM;
+
+        trace.nr_entries        = 0;
+        trace.max_entries       = MAX_STACK_TRACE_DEPTH;
+        trace.entries           = entries;
+        trace.skip              = 0;
+        save_stack_trace_tsk(task, &trace);
+
+        for (i = 0; i < trace.nr_entries; i++) {
+                seq_printf(m, "[<%p>] %pS\n",
+                           (void *)entries[i], (void *)entries[i]);
+        }
+        kfree(entries);
+
+        return 0;
+}
+#endif
+
 #ifdef CONFIG_SCHEDSTATS
 /*
  * Provides /proc/PID/schedstat
@@ -2500,6 +2532,9 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_KALLSYMS
         INF("wchan",      S_IRUGO, proc_pid_wchan),
 #endif
+#ifdef CONFIG_STACKTRACE
+        ONE("stack",      S_IRUSR, proc_pid_stack),
+#endif
 #ifdef CONFIG_SCHEDSTATS
         INF("schedstat",  S_IRUGO, proc_pid_schedstat),
 #endif
@@ -2835,6 +2870,9 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_KALLSYMS
         INF("wchan",     S_IRUGO, proc_pid_wchan),
 #endif
+#ifdef CONFIG_STACKTRACE
+        ONE("stack",      S_IRUSR, proc_pid_stack),
+#endif
 #ifdef CONFIG_SCHEDSTATS
         INF("schedstat", S_IRUGO, proc_pid_schedstat),
 #endif