[for-linus][PATCH 0/2] tracing: A couple of fixes for 6.13

[for-linus][PATCH 0/2] tracing: A couple of fixes for 6.13

[Steven Rostedt]

tracing fixes for v6.13:

- Fix trace histogram sort function cmp_entries_dup()

  The sort function cmp_entries_dup() returns either 1 or 0, and not
  -1 if parameter "a" is less than "b" by memcmp().

- Fix archs that call trace_hardirqs_off() without RCU watching

  Both x86 and arm64 no longer call any tracepoints with RCU not
  watching. It was assumed that it was safe to get rid of
  trace_*_rcuidle() version of the tracepoint calls. This was needed
  to get rid of the SRCU protection and be able to implement features
  like faultable traceponits and add rust tracepoints.

  Unfortunately, there were a few architectures that still relied on
  that logic. There's only one file that has tracepoints that are
  called without RCU watching. Add macro logic around the tracepoints
  for architectures that do not have CONFIG_ARCH_WANTS_NO_INSTR defined
  will check if the code is in the idle path (the only place RCU isn't
  watching), and enable RCU around calling the tracepoint, but only
  do it if the tracepoint is enabled.

  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
trace/fixes

Head SHA1: 2f88ccdee3326a6197573623cd31947391eb5579


Kuan-Wei Chiu (1):
      tracing: Fix cmp_entries_dup() to respect sort() comparison rules

Steven Rostedt (1):
      tracing: Fix archs that still call tracepoints without RCU watching

----
 kernel/trace/trace_preemptirq.c | 43 +++++++++++++++++++++++++++++++++++------
 kernel/trace/tracing_map.c      |  6 +-----
 2 files changed, 38 insertions(+), 11 deletions(-)

[for-linus][PATCH 1/2] tracing: Fix cmp_entries_dup() to respect sort() comparison rules

[Steven Rostedt]

From: Kuan-Wei Chiu <visitorckw@gmail.com>

The cmp_entries_dup() function used as the comparator for sort()
violated the symmetry and transitivity properties required by the
sorting algorithm. Specifically, it returned 1 whenever memcmp() was
non-zero, which broke the following expectations:

* Symmetry: If x < y, then y > x.
* Transitivity: If x < y and y < z, then x < z.

These violations could lead to incorrect sorting and failure to
correctly identify duplicate elements.

Fix the issue by directly returning the result of memcmp(), which
adheres to the required comparison properties.

Cc: stable@vger.kernel.org
Fixes: 08d43a5fa063 ("tracing: Add lock-free tracing_map")
Link: https://lore.kernel.org/20241203202228.1274403-1-visitorckw@gmail.com
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/tracing_map.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/trace/tracing_map.c b/kernel/trace/tracing_map.c
index 3a56e7c8aa4f..1921ade45be3 100644
--- a/kernel/trace/tracing_map.c
+++ b/kernel/trace/tracing_map.c
@@ -845,15 +845,11 @@ int tracing_map_init(struct tracing_map *map)
 static int cmp_entries_dup(const void *A, const void *B)
 {
 	const struct tracing_map_sort_entry *a, *b;
-	int ret = 0;
 
 	a = *(const struct tracing_map_sort_entry **)A;
 	b = *(const struct tracing_map_sort_entry **)B;
 
-	if (memcmp(a->key, b->key, a->elt->map->key_size))
-		ret = 1;
-
-	return ret;
+	return memcmp(a->key, b->key, a->elt->map->key_size);
 }
 
 static int cmp_entries_sum(const void *A, const void *B)
-- 
2.45.2

[for-linus][PATCH 2/2] tracing: Fix archs that still call tracepoints without RCU watching

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

Tracepoints require having RCU "watching" as it uses RCU to do updates to
the tracepoints. There are some cases that would call a tracepoint when
RCU was not "watching". This was usually in the idle path where RCU has
"shutdown". For the few locations that had tracepoints without RCU
watching, there was an trace_*_rcuidle() variant that could be used. This
used SRCU for protection.

There are tracepoints that trace when interrupts and preemption are
enabled and disabled. In some architectures, these tracepoints are called
in a path where RCU is not watching. When x86 and arm64 removed these
locations, it was incorrectly assumed that it would be safe to remove the
trace_*_rcuidle() variant and also remove the SRCU logic, as it made the
code more complex and harder to implement new tracepoint features (like
faultable tracepoints and tracepoints in rust).

Instead of bringing back the trace_*_rcuidle(), as it will not be trivial
to do as new code has already been added depending on its removal, add a
workaround to the one file that still requires it (trace_preemptirq.c). If
the architecture does not define CONFIG_ARCH_WANTS_NO_INSTR, then check if
the code is in the idle path, and if so, call ct_irq_enter/exit() which
will enable RCU around the tracepoint.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/20241204100414.4d3e06d0@gandalf.local.home
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Fixes: 48bcda684823 ("tracing: Remove definition of trace_*_rcuidle()")
Closes: https://lore.kernel.org/all/bddb02de-957a-4df5-8e77-829f55728ea2@roeck-us.net/
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_preemptirq.c | 43 ++++++++++++++++++++++++++++-----
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_preemptirq.c b/kernel/trace/trace_preemptirq.c
index 5c03633316a6..0c42b15c3800 100644
--- a/kernel/trace/trace_preemptirq.c
+++ b/kernel/trace/trace_preemptirq.c
@@ -10,11 +10,42 @@
 #include <linux/module.h>
 #include <linux/ftrace.h>
 #include <linux/kprobes.h>
+#include <linux/hardirq.h>
 #include "trace.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/preemptirq.h>
 
+/*
+ * Use regular trace points on architectures that implement noinstr
+ * tooling: these calls will only happen with RCU enabled, which can
+ * use a regular tracepoint.
+ *
+ * On older architectures, RCU may not be watching in idle. In that
+ * case, wake up RCU to watch while calling the tracepoint. These
+ * aren't NMI-safe - so exclude NMI contexts:
+ */
+#ifdef CONFIG_ARCH_WANTS_NO_INSTR
+#define trace(point, args)	trace_##point(args)
+#else
+#define trace(point, args)					\
+	do {							\
+		if (trace_##point##_enabled()) {		\
+			bool exit_rcu = false;			\
+			if (in_nmi())				\
+				break;				\
+			if (!IS_ENABLED(CONFIG_TINY_RCU) &&	\
+			    is_idle_task(current)) {		\
+				ct_irq_enter();			\
+				exit_rcu = true;		\
+			}					\
+			trace_##point(args);			\
+			if (exit_rcu)				\
+				ct_irq_exit();			\
+		}						\
+	} while (0)
+#endif
+
 #ifdef CONFIG_TRACE_IRQFLAGS
 /* Per-cpu variable to prevent redundant calls when IRQs already off */
 static DEFINE_PER_CPU(int, tracing_irq_cpu);
@@ -28,7 +59,7 @@ static DEFINE_PER_CPU(int, tracing_irq_cpu);
 void trace_hardirqs_on_prepare(void)
 {
 	if (this_cpu_read(tracing_irq_cpu)) {
-		trace_irq_enable(CALLER_ADDR0, CALLER_ADDR1);
+		trace(irq_enable, TP_ARGS(CALLER_ADDR0, CALLER_ADDR1));
 		tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
 		this_cpu_write(tracing_irq_cpu, 0);
 	}
@@ -39,7 +70,7 @@ NOKPROBE_SYMBOL(trace_hardirqs_on_prepare);
 void trace_hardirqs_on(void)
 {
 	if (this_cpu_read(tracing_irq_cpu)) {
-		trace_irq_enable(CALLER_ADDR0, CALLER_ADDR1);
+		trace(irq_enable, TP_ARGS(CALLER_ADDR0, CALLER_ADDR1));
 		tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
 		this_cpu_write(tracing_irq_cpu, 0);
 	}
@@ -61,7 +92,7 @@ void trace_hardirqs_off_finish(void)
 	if (!this_cpu_read(tracing_irq_cpu)) {
 		this_cpu_write(tracing_irq_cpu, 1);
 		tracer_hardirqs_off(CALLER_ADDR0, CALLER_ADDR1);
-		trace_irq_disable(CALLER_ADDR0, CALLER_ADDR1);
+		trace(irq_disable, TP_ARGS(CALLER_ADDR0, CALLER_ADDR1));
 	}
 
 }
@@ -75,7 +106,7 @@ void trace_hardirqs_off(void)
 	if (!this_cpu_read(tracing_irq_cpu)) {
 		this_cpu_write(tracing_irq_cpu, 1);
 		tracer_hardirqs_off(CALLER_ADDR0, CALLER_ADDR1);
-		trace_irq_disable(CALLER_ADDR0, CALLER_ADDR1);
+		trace(irq_disable, TP_ARGS(CALLER_ADDR0, CALLER_ADDR1));
 	}
 }
 EXPORT_SYMBOL(trace_hardirqs_off);
@@ -86,13 +117,13 @@ NOKPROBE_SYMBOL(trace_hardirqs_off);
 
 void trace_preempt_on(unsigned long a0, unsigned long a1)
 {
-	trace_preempt_enable(a0, a1);
+	trace(preempt_enable, TP_ARGS(a0, a1));
 	tracer_preempt_on(a0, a1);
 }
 
 void trace_preempt_off(unsigned long a0, unsigned long a1)
 {
-	trace_preempt_disable(a0, a1);
+	trace(preempt_disable, TP_ARGS(a0, a1));
 	tracer_preempt_off(a0, a1);
 }
 #endif
-- 
2.45.2