[ARM] latencytop support

Available for !SMP only at the moment.

From Russell:

|Basically, if a thread is running on a CPU, thread_saved_fp() is invalid.
|So, the question is: what guarantees do we have here that 'tsk' is not
|running on another CPU?

Signed-off-by: Nicolas Pitre <nico@marvell.com>
Tested-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>

2 files changed, 35 insertions, 4 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b786e68914d4..a91b9ac9a0e5 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -84,6 +84,11 @@ config STACKTRACE_SUPPORT
         bool
         default y
 
+config HAVE_LATENCYTOP_SUPPORT
+        bool
+        depends on !SMP
+        default y
+
 config LOCKDEP_SUPPORT
         bool
         default y
diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
index ae31deb2d065..90e0c35ae60d 100644
--- a/arch/arm/kernel/stacktrace.c
+++ b/arch/arm/kernel/stacktrace.c
@@ -36,6 +36,7 @@ EXPORT_SYMBOL(walk_stackframe);
 #ifdef CONFIG_STACKTRACE
 struct stack_trace_data {
         struct stack_trace *trace;
+        unsigned int no_sched_functions;
         unsigned int skip;
 };
 
@@ -43,27 +44,52 @@ static int save_trace(struct stackframe *frame, void *d)
 {
         struct stack_trace_data *data = d;
         struct stack_trace *trace = data->trace;
+        unsigned long addr = frame->lr;
 
+        if (data->no_sched_functions && in_sched_functions(addr))
+                return 0;
         if (data->skip) {
                 data->skip--;
                 return 0;
         }
 
-        trace->entries[trace->nr_entries++] = frame->lr;
+        trace->entries[trace->nr_entries++] = addr;
 
         return trace->nr_entries >= trace->max_entries;
 }
 
-void save_stack_trace(struct stack_trace *trace)
+void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 {
         struct stack_trace_data data;
         unsigned long fp, base;
 
         data.trace = trace;
         data.skip = trace->skip;
-        base = (unsigned long)task_stack_page(current);
-        asm("mov %0, fp" : "=r" (fp));
+        base = (unsigned long)task_stack_page(tsk);
+
+        if (tsk != current) {
+#ifdef CONFIG_SMP
+                /*
+                 * What guarantees do we have here that 'tsk'
+                 * is not running on another CPU?
+                 */
+                BUG();
+#else
+                data.no_sched_functions = 1;
+                fp = thread_saved_fp(tsk);
+#endif
+        } else {
+                data.no_sched_functions = 0;
+                asm("mov %0, fp" : "=r" (fp));
+        }
 
         walk_stackframe(fp, base, base + THREAD_SIZE, save_trace, &data);
+        if (trace->nr_entries < trace->max_entries)
+                trace->entries[trace->nr_entries++] = ULONG_MAX;
+}
+
+void save_stack_trace(struct stack_trace *trace)
+{
+        save_stack_trace_tsk(current, trace);
 }
 #endif