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>

1 files changed, 18 insertions, 6 deletions

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);