1 files changed, 210 insertions, 0 deletions
diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
new file mode 100644
index 000000000000..c303f7a114e9
--- /dev/null
+++ b/include/linux/trace_recursion.h
@@ -0,0 +1,210 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_TRACE_RECURSION_H
+#define _LINUX_TRACE_RECURSION_H
+
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+
+#ifdef CONFIG_TRACING
+
+/* Only current can touch trace_recursion */
+
+/*
+ * For function tracing recursion:
+ *  The order of these bits are important.
+ *
+ *  When function tracing occurs, the following steps are made:
+ *   If arch does not support a ftrace feature:
+ *    call internal function (uses INTERNAL bits) which calls...
+ *   The function callback, which can use the FTRACE bits to
+ *    check for recursion.
+ */
+enum {
+	/* Function recursion bits */
+	TRACE_FTRACE_BIT,
+	TRACE_FTRACE_NMI_BIT,
+	TRACE_FTRACE_IRQ_BIT,
+	TRACE_FTRACE_SIRQ_BIT,
+	TRACE_FTRACE_TRANSITION_BIT,
+
+	/* Internal use recursion bits */
+	TRACE_INTERNAL_BIT,
+	TRACE_INTERNAL_NMI_BIT,
+	TRACE_INTERNAL_IRQ_BIT,
+	TRACE_INTERNAL_SIRQ_BIT,
+	TRACE_INTERNAL_TRANSITION_BIT,
+
+	TRACE_BRANCH_BIT,
+/*
+ * Abuse of the trace_recursion.
+ * As we need a way to maintain state if we are tracing the function
+ * graph in irq because we want to trace a particular function that
+ * was called in irq context but we have irq tracing off. Since this
+ * can only be modified by current, we can reuse trace_recursion.
+ */
+	TRACE_IRQ_BIT,
+
+	/* Set if the function is in the set_graph_function file */
+	TRACE_GRAPH_BIT,
+
+	/*
+	 * In the very unlikely case that an interrupt came in
+	 * at a start of graph tracing, and we want to trace
+	 * the function in that interrupt, the depth can be greater
+	 * than zero, because of the preempted start of a previous
+	 * trace. In an even more unlikely case, depth could be 2
+	 * if a softirq interrupted the start of graph tracing,
+	 * followed by an interrupt preempting a start of graph
+	 * tracing in the softirq, and depth can even be 3
+	 * if an NMI came in at the start of an interrupt function
+	 * that preempted a softirq start of a function that
+	 * preempted normal context!!!! Luckily, it can't be
+	 * greater than 3, so the next two bits are a mask
+	 * of what the depth is when we set TRACE_GRAPH_BIT
+	 */
+
+	TRACE_GRAPH_DEPTH_START_BIT,
+	TRACE_GRAPH_DEPTH_END_BIT,
+
+	/*
+	 * To implement set_graph_notrace, if this bit is set, we ignore
+	 * function graph tracing of called functions, until the return
+	 * function is called to clear it.
+	 */
+	TRACE_GRAPH_NOTRACE_BIT,
+
+	/* Used to prevent recursion recording from recursing. */
+	TRACE_RECORD_RECURSION_BIT,
+};
+
+#define trace_recursion_set(bit)	do { (current)->trace_recursion |= (1<<(bit)); } while (0)
+#define trace_recursion_clear(bit)	do { (current)->trace_recursion &= ~(1<<(bit)); } while (0)
+#define trace_recursion_test(bit)	((current)->trace_recursion & (1<<(bit)))
+
+#define trace_recursion_depth() \
+	(((current)->trace_recursion >> TRACE_GRAPH_DEPTH_START_BIT) & 3)
+#define trace_recursion_set_depth(depth) \
+	do {								\
+		current->trace_recursion &=				\
+			~(3 << TRACE_GRAPH_DEPTH_START_BIT);		\
+		current->trace_recursion |=				\
+			((depth) & 3) << TRACE_GRAPH_DEPTH_START_BIT;	\
+	} while (0)
+
+#define TRACE_CONTEXT_BITS	4
+
+#define TRACE_FTRACE_START	TRACE_FTRACE_BIT
+
+#define TRACE_LIST_START	TRACE_INTERNAL_BIT
+
+#define TRACE_CONTEXT_MASK	((1 << (TRACE_LIST_START + TRACE_CONTEXT_BITS)) - 1)
+
+/*
+ * Used for setting context
+ *  NMI     = 0
+ *  IRQ     = 1
+ *  SOFTIRQ = 2
+ *  NORMAL  = 3
+ */
+enum {
+	TRACE_CTX_NMI,
+	TRACE_CTX_IRQ,
+	TRACE_CTX_SOFTIRQ,
+	TRACE_CTX_NORMAL,
+	TRACE_CTX_TRANSITION,
+};
+
+static __always_inline int trace_get_context_bit(void)
+{
+	unsigned char bit = interrupt_context_level();
+
+	return TRACE_CTX_NORMAL - bit;
+}
+
+#ifdef CONFIG_FTRACE_RECORD_RECURSION
+extern void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip);
+# define do_ftrace_record_recursion(ip, pip)				\
+	do {								\
+		if (!trace_recursion_test(TRACE_RECORD_RECURSION_BIT)) { \
+			trace_recursion_set(TRACE_RECORD_RECURSION_BIT); \
+			ftrace_record_recursion(ip, pip);		\
+			trace_recursion_clear(TRACE_RECORD_RECURSION_BIT); \
+		}							\
+	} while (0)
+#else
+# define do_ftrace_record_recursion(ip, pip)	do { } while (0)
+#endif
+
+/*
+ * Preemption is promised to be disabled when return bit >= 0.
+ */
+static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip,
+							int start)
+{
+	unsigned int val = READ_ONCE(current->trace_recursion);
+	int bit;
+
+	bit = trace_get_context_bit() + start;
+	if (unlikely(val & (1 << bit))) {
+		/*
+		 * If an interrupt occurs during a trace, and another trace
+		 * happens in that interrupt but before the preempt_count is
+		 * updated to reflect the new interrupt context, then this
+		 * will think a recursion occurred, and the event will be dropped.
+		 * Let a single instance happen via the TRANSITION_BIT to
+		 * not drop those events.
+		 */
+		bit = TRACE_CTX_TRANSITION + start;
+		if (val & (1 << bit)) {
+			do_ftrace_record_recursion(ip, pip);
+			return -1;
+		}
+	}
+
+	val |= 1 << bit;
+	current->trace_recursion = val;
+	barrier();
+
+	preempt_disable_notrace();
+
+	return bit;
+}
+
+/*
+ * Preemption will be enabled (if it was previously enabled).
+ */
+static __always_inline void trace_clear_recursion(int bit)
+{
+	preempt_enable_notrace();
+	barrier();
+	trace_recursion_clear(bit);
+}
+
+/**
+ * ftrace_test_recursion_trylock - tests for recursion in same context
+ *
+ * Use this for ftrace callbacks. This will detect if the function
+ * tracing recursed in the same context (normal vs interrupt),
+ *
+ * Returns: -1 if a recursion happened.
+ *           >= 0 if no recursion.
+ */
+static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
+							 unsigned long parent_ip)
+{
+	return trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START);
+}
+
+/**
+ * ftrace_test_recursion_unlock - called when function callback is complete
+ * @bit: The return of a successful ftrace_test_recursion_trylock()
+ *
+ * This is used at the end of a ftrace callback.
+ */
+static __always_inline void ftrace_test_recursion_unlock(int bit)
+{
+	trace_clear_recursion(bit);
+}
+
+#endif /* CONFIG_TRACING */
+#endif /* _LINUX_TRACE_RECURSION_H */