[PATCH 2/9] ftrace: Add ftrace_test_recursion_trylock() helper function

Steven Rostedt
2020-10-29T00:58:59Z

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

To make it easier for ftrace callbacks to have recursion protection, provide
a ftrace_test_recursion_trylock() and ftrace_test_recursion_unlock() helper
that tests for recursion.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
include/linux/trace_recursion.h | 25 +++++++++++++++++++++++++
kernel/trace/trace_functions.c | 12 +++++-------
2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
index 6c94c2ece9f0..da17a1144bf4 100644
--- a/include/linux/trace_recursion.h
+++ b/include/linux/trace_recursion.h
@@ -163,5 +163,30 @@ static __always_inline void trace_clear_recursion(int bit)
current->trace_recursion = val;
}

+/**
+ * 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(void)
+{
+ return trace_test_and_set_recursion(TRACE_FTRACE_START, TRACE_FTRACE_MAX);
+}
+
+/**
+ * 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 */
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 2c2126e1871d..943756c01190 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -141,22 +141,20 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
if (unlikely(!tr->function_enabled))
return;

+ bit = ftrace_test_recursion_trylock();
+ if (bit < 0)
+ return;
+
pc = preempt_count();
preempt_disable_notrace();

- bit = trace_test_and_set_recursion(TRACE_FTRACE_START, TRACE_FTRACE_MAX);
- if (bit < 0)
- goto out;
-
cpu = smp_processor_id();
data = per_cpu_ptr(tr->array_buffer.data, cpu);
if (!atomic_read(&data->disabled)) {
local_save_flags(flags);
trace_function(tr, ip, parent_ip, flags, pc);
}
- trace_clear_recursion(bit);
-
- out:
+ ftrace_test_recursion_unlock(bit);
preempt_enable_notrace();
}

--
2.28.0