ftrace: Add context level recursion bit checking

Currently for recursion checking in the function tracer, ftrace
tests a task_struct bit to determine if the function tracer had
recursed or not. If it has, then it will will return without going
further.

But this leads to races. If an interrupt came in after the bit
was set, the functions being traced would see that bit set and
think that the function tracer recursed on itself, and would return.

Instead add a bit for each context (normal, softirq, irq and nmi).

A check of which context the task is in is made before testing the
associated bit. Now if an interrupt preempts the function tracer
after the previous context has been set, the interrupt functions
can still be traced.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 33 insertions, 7 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 1330969d8447..639b6ab1f04c 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -156,14 +156,27 @@ static void
 ftrace_global_list_func(unsigned long ip, unsigned long parent_ip,
 			struct ftrace_ops *op, struct pt_regs *regs)
 {
-	if (unlikely(trace_recursion_test(TRACE_GLOBAL_BIT)))
+	int bit;
+
+	if (in_interrupt()) {
+		if (in_nmi())
+			bit = TRACE_GLOBAL_NMI_BIT;
+
+		else if (in_irq())
+			bit = TRACE_GLOBAL_IRQ_BIT;
+		else
+			bit = TRACE_GLOBAL_SIRQ_BIT;
+	} else
+		bit = TRACE_GLOBAL_BIT;
+
+	if (unlikely(trace_recursion_test(bit)))
 		return;
 
-	trace_recursion_set(TRACE_GLOBAL_BIT);
+	trace_recursion_set(bit);
 	do_for_each_ftrace_op(op, ftrace_global_list) {
 		op->func(ip, parent_ip, op, regs);
 	} while_for_each_ftrace_op(op);
-	trace_recursion_clear(TRACE_GLOBAL_BIT);
+	trace_recursion_clear(bit);
 }
 
 static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip,
@@ -4132,14 +4145,27 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
 		       struct ftrace_ops *ignored, struct pt_regs *regs)
 {
 	struct ftrace_ops *op;
+	unsigned int bit;
 
 	if (function_trace_stop)
 		return;
 
-	if (unlikely(trace_recursion_test(TRACE_INTERNAL_BIT)))
-		return;
+	if (in_interrupt()) {
+		if (in_nmi())
+			bit = TRACE_INTERNAL_NMI_BIT;
+
+		else if (in_irq())
+			bit = TRACE_INTERNAL_IRQ_BIT;
+		else
+			bit = TRACE_INTERNAL_SIRQ_BIT;
+	} else
+		bit = TRACE_INTERNAL_BIT;
+
+	if (unlikely(trace_recursion_test(bit)))
+			return;
+
+	trace_recursion_set(bit);
 
-	trace_recursion_set(TRACE_INTERNAL_BIT);
 	/*
 	 * Some of the ops may be dynamically allocated,
 	 * they must be freed after a synchronize_sched().
@@ -4150,7 +4176,7 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
 			op->func(ip, parent_ip, op, regs);
 	} while_for_each_ftrace_op(op);
 	preempt_enable_notrace();
-	trace_recursion_clear(TRACE_INTERNAL_BIT);
+	trace_recursion_clear(bit);
 }
 
 /*