Re: [PATCH] tracing: Have all levels of checks prevent recursion

[Steven Rostedt <rostedt@xxxxxxxxxxx>]

On Fri, 15 Oct 2021 20:04:29 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> On Fri, Oct 15, 2021 at 01:58:06PM -0400, Steven Rostedt wrote:
> > Something like this:  
> 
> I think having one copy of that in a header is better than having 3
> copies. But yes, something along them lines.

I was just about to ask you about this patch ;-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 4d244e295e85..a6ae329aa654 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -74,6 +74,27 @@
  */
 #define FORK_PREEMPT_COUNT	(2*PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
 
+/**
+ * interrupt_context_level - return interrupt context level
+ *
+ * Returns the current interrupt context level.
+ *  0 - normal context
+ *  1 - softirq context
+ *  2 - hardirq context
+ *  3 - NMI context
+ */
+static __always_inline unsigned char interrupt_context_level(void)
+{
+	unsigned long pc = preempt_count();
+	unsigned char level = 0;
+
+	level += !!(pc & (NMI_MASK));
+	level += !!(pc & (NMI_MASK | HARDIRQ_MASK));
+	level += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
+
+	return level;
+}
+
 /* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */
 #include <asm/preempt.h>
 
diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
index 41f5bfd9e93f..018a04381556 100644
--- a/include/linux/trace_recursion.h
+++ b/include/linux/trace_recursion.h
@@ -118,12 +118,7 @@ enum {
 
 static __always_inline int trace_get_context_bit(void)
 {
-	unsigned long pc = preempt_count();
-	unsigned char bit = 0;
-
-	bit += !!(pc & (NMI_MASK));
-	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK));
-	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
+	unsigned char bit = interrupt_context_level();
 
 	return TRACE_CTX_NORMAL - bit;
 }
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 228801e20788..c91711f20cf8 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -206,11 +206,7 @@ DEFINE_OUTPUT_COPY(__output_copy_user, arch_perf_out_copy_user)
 static inline int get_recursion_context(int *recursion)
 {
 	unsigned int pc = preempt_count();
-	unsigned char rctx = 0;
-
-	rctx += !!(pc & (NMI_MASK));
-	rctx += !!(pc & (NMI_MASK | HARDIRQ_MASK));
-	rctx += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
+	unsigned char rctx = interrupt_context_level();
 
 	if (recursion[rctx])
 		return -1;
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 15d4380006e3..f6520d0a4c8c 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3167,12 +3167,7 @@ static __always_inline int
 trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	unsigned int val = cpu_buffer->current_context;
-	unsigned long pc = preempt_count();
-	int bit = 0;
-
-	bit += !!(pc & (NMI_MASK));
-	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK));
-	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
+	int bit = interrupt_context_level();
 
 	bit = RB_CTX_NORMAL - bit;