Patch "tracing: Reuse logic from perf's get_recursion_context()" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tracing: Reuse logic from perf's get_recursion_context()

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tracing-reuse-logic-from-perf-s-get_recursion_contex.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8cb02f2bcd2b069555e2d48c61a3a565d308b512
Author: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Date:   Fri Oct 15 13:42:40 2021 -0400

    tracing: Reuse logic from perf's get_recursion_context()
    
    [ Upstream commit 9b84fadc444de5456ab5f5487e2108311c724c3f ]
    
    Instead of having branches that adds noise to the branch prediction, use
    the addition logic to set the bit for the level of interrupt context that
    the state is currently in. This copies the logic from perf's
    get_recursion_context() function.
    
    Link: https://lore.kernel.org/all/20211015161702.GF174703@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
    
    Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
    Stable-dep-of: 87c3a5893e86 ("sched/core: Optimize in_task() and in_interrupt() a bit")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
index fe95f09225266..00acd7dca7a7d 100644
--- a/include/linux/trace_recursion.h
+++ b/include/linux/trace_recursion.h
@@ -117,12 +117,13 @@ enum {
 static __always_inline int trace_get_context_bit(void)
 {
 	unsigned long pc = preempt_count();
+	unsigned char bit = 0;
 
-	if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
-		return TRACE_CTX_NORMAL;
-	else
-		return pc & NMI_MASK ? TRACE_CTX_NMI :
-			pc & HARDIRQ_MASK ? TRACE_CTX_IRQ : TRACE_CTX_SOFTIRQ;
+	bit += !!(pc & (NMI_MASK));
+	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK));
+	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
+
+	return TRACE_CTX_NORMAL - bit;
 }
 
 #ifdef CONFIG_FTRACE_RECORD_RECURSION
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index e5dc7b5a261c6..c3c9960c9f27b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3250,13 +3250,13 @@ trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	unsigned int val = cpu_buffer->current_context;
 	unsigned long pc = preempt_count();
-	int bit;
+	int bit = 0;
 
-	if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
-		bit = RB_CTX_NORMAL;
-	else
-		bit = pc & NMI_MASK ? RB_CTX_NMI :
-			pc & HARDIRQ_MASK ? RB_CTX_IRQ : RB_CTX_SOFTIRQ;
+	bit += !!(pc & (NMI_MASK));
+	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK));
+	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
+
+	bit = RB_CTX_NORMAL - bit;
 
 	if (unlikely(val & (1 << (bit + cpu_buffer->nest)))) {
 		/*