Re: [PATCH v3 1/2] ftrace: disable preemption between ftrace_test_recursion_trylock/unlock()

On 2021/10/15 上午11:13, 王贇 wrote:
[snip]

quoted

 # define do_ftrace_record_recursion(ip, pip)	do { } while (0)
 #endif
 
+/*
+ * trace_test_and_set_recursion() is called on several layers
+ * of the ftrace code when handling the same ftrace entry.
+ * These calls might be nested/recursive.
+ *
+ * It uses TRACE_LIST_*BITs to distinguish between this
+ * internal recursion and recursion caused by calling
+ * the traced function by the ftrace code.
+ *
+ * Returns: > 0 when no recursion
+ *          0 when called recursively internally (safe)

The 0 can also happened when ftrace handler recursively called trylock()
under the same context, or not?

Never mind... you're right about this.

Regards,
Michael Wang

Regards,
Michael Wang

quoted

+ *	    -1 when the traced function was called recursively from
+ *             the ftrace handler (unsafe)
+ */
 static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip,
 							int start, int max)
 {
 	unsigned int val = READ_ONCE(current->trace_recursion);
 	int bit;
 
-	/* A previous recursion check was made */
+	/* Called recursively internally by different ftrace code layers? */
 	if ((val & TRACE_CONTEXT_MASK) > max)
 		return 0;

quoted