Patchwork powerpc/ftrace: Trace function graph entry before updating index

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Submitter Steven Rostedt
Date July 18, 2012, 10:35 p.m.
Message ID <1342650928.11900.20.camel@gandalf.stny.rr.com>
Download mbox | patch
Permalink /patch/171851/
State Accepted, archived
Commit bac821a6e3404330d509fd3a245bf7701f210c7c
Delegated to: Benjamin Herrenschmidt
Headers show

Comments

Steven Rostedt - July 18, 2012, 10:35 p.m.
As Colin Cross ported my x86 change to ARM, he also pointed out that
powerpc is also behind in this fix.

The commit 722b3c746953 "ftrace/graph: Trace function entry before
updating index" fixes an issue with function graph tracing for x86,
where if the called entry function decides not to trace interrupts, it
can fail the check if an interrupt comes in just after the
curr_ret_stack is updated.

The solution is to call the entry function first, then update the
curr_ret_stack if the entry function wants to be traced.

Cc: Colin Cross <ccross@android.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Patch

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 91b46b7..1fb7856 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -630,18 +630,17 @@  void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
 		return;
 	}
 
-	if (ftrace_push_return_trace(old, self_addr, &trace.depth, 0) == -EBUSY) {
-		*parent = old;
-		return;
-	}
-
 	trace.func = self_addr;
+	trace.depth = current->curr_ret_stack + 1;
 
 	/* Only trace if the calling function expects to */
 	if (!ftrace_graph_entry(&trace)) {
-		current->curr_ret_stack--;
 		*parent = old;
+		return;
 	}
+
+	if (ftrace_push_return_trace(old, self_addr, &trace.depth, 0) == -EBUSY)
+		*parent = old;
 }
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */