[PATCH 2/2] Some stacks show up untracable, so fall back to old method in this case

[Gregory Haskins]

Signed-off-by: Gregory Haskins <[EMAIL PROTECTED]>
---

 arch/x86_64/kernel/stacktrace.c |   10 ++++++++--
 include/linux/stacktrace.h      |    1 +
 kernel/latency_trace.c          |   12 ++++++++++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/arch/x86_64/kernel/stacktrace.c b/arch/x86_64/kernel/stacktrace.c
index cb91091..054f627 100644
--- a/arch/x86_64/kernel/stacktrace.c
+++ b/arch/x86_64/kernel/stacktrace.c
@@ -24,7 +24,7 @@ static int save_stack_stack(void *data, char *name)
        return -1;
 }
 
-static void save_stack_address(void *data, unsigned long addr)
+static void _save_stack_address(void *data, unsigned long addr)
 {
        struct stack_trace *trace = (struct stack_trace *)data;
        if (trace->skip > 0) {
@@ -39,7 +39,7 @@ static struct stacktrace_ops save_stack_ops = {
        .warning = save_stack_warning,
        .warning_symbol = save_stack_warning_symbol,
        .stack = save_stack_stack,
-       .address = save_stack_address,
+       .address = _save_stack_address,
 };
 
 /*
@@ -52,3 +52,9 @@ void save_stack_trace(struct stack_trace *trace)
                trace->entries[trace->nr_entries++] = ULONG_MAX;
 }
 EXPORT_SYMBOL(save_stack_trace);
+
+void save_stack_address(struct stack_trace *trace, unsigned long addr)
+{
+       _save_stack_address(trace, addr);
+}
+EXPORT_SYMBOL(save_stack_address);
diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
index e7fa657..5acad27 100644
--- a/include/linux/stacktrace.h
+++ b/include/linux/stacktrace.h
@@ -9,6 +9,7 @@ struct stack_trace {
 };
 
 extern void save_stack_trace(struct stack_trace *trace);
+extern void save_stack_address(struct stack_trace *trace, unsigned long addr);
 
 extern void print_stack_trace(struct stack_trace *trace, int spaces);
 #else
diff --git a/kernel/latency_trace.c b/kernel/latency_trace.c
index 9b83262..82c04ac 100644
--- a/kernel/latency_trace.c
+++ b/kernel/latency_trace.c
@@ -2058,6 +2058,18 @@ void notrace add_preempt_count(unsigned int val)
                        trace->entries = current->preempt_trace[idx].data;
 
                        save_stack_trace(trace);
+
+                       /*
+                        * If we couldnt get our trace, the first entry will
+                        * have the ULONG_MAX marker.  In that case, we
+                        * rewind and save our simple two level stack
+                        */
+                       if ((trace->nr_entries == 1)
+                           && (trace->entries[0] == ULONG_MAX)) {
+                               trace->nr_entries = 0;
+                               save_stack_address(trace, eip);
+                               save_stack_address(trace, parent_eip);
+                       }
                }
        }
 #endif

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