[for-next][PATCH 0/2] ftrace: Updates for v7.3

[for-next][PATCH 0/2] ftrace: Updates for v7.3

[Steven Rostedt]

  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
ftrace/for-next

Head SHA1: 88b3e7fedc07d940c32eb5c0733a780e944b6b47


Andrey Grodzovsky (2):
      ftrace: deprecate disabling via ftrace_enabled sysctl
      selftests/livepatch: update test-ftrace.sh for deprecated ftrace_enabled

----
 Documentation/trace/ftrace.rst                   |  5 +++
 kernel/trace/ftrace.c                            | 43 ++++------------------
 tools/testing/selftests/livepatch/functions.sh   | 14 ++++++++
 tools/testing/selftests/livepatch/test-ftrace.sh | 45 +++++++++++++++---------
 4 files changed, 53 insertions(+), 54 deletions(-)

[for-next][PATCH 1/2] ftrace: deprecate disabling via ftrace_enabled sysctl

[Steven Rostedt]

From: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>

Writing 0 to kernel.ftrace_enabled has not reliably disabled ftrace
for years (FTRACE_OPS_FL_PERMANENT users already block it, and more
callers rely on ftrace always being on). Refuse the write instead of
leaving it in an inconsistent "disables some, not all" state: return
-EOPNOTSUPP and log a message. Reads and enabling (writing 1) are
unaffected.

Update the docs to note the deprecation up front.

Link: https://patch.msgid.link/20260806153000.4184871-2-andrey.grodzovsky@crowdstrike.com
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 Documentation/trace/ftrace.rst |  5 ++++
 kernel/trace/ftrace.c          | 43 +++++-----------------------------
 2 files changed, 11 insertions(+), 37 deletions(-)

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 84f06bf0da9b..7261f25f8b4b 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -3313,6 +3313,11 @@ this special filter via::
 ftrace_enabled
 --------------
 
+.. note::
+   Disabling ftrace via this switch is deprecated. Writing 0 is refused
+   with -EOPNOTSUPP and logs a warning; writing 1 and reading the value
+   are unaffected.
+
 Note, the proc sysctl ftrace_enable is a big on/off switch for the
 function tracer. By default it is enabled (when function tracing is
 enabled in the kernel). If it is disabled, all function tracing is
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 6c47a94f5924..d1989958d6b2 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -9370,38 +9370,10 @@ static void ftrace_startup_sysctl(void)
 	}
 }
 
-static void ftrace_shutdown_sysctl(void)
-{
-	int command;
-
-	if (unlikely(ftrace_disabled))
-		return;
-
-	/* ftrace_start_up is true if ftrace is running */
-	if (ftrace_start_up) {
-		command = FTRACE_DISABLE_CALLS;
-		if (ftrace_graph_active)
-			command |= FTRACE_STOP_FUNC_RET;
-		ftrace_run_update_code(command);
-	}
-}
 #else
 # define ftrace_startup_sysctl()       do { } while (0)
-# define ftrace_shutdown_sysctl()      do { } while (0)
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
-static bool is_permanent_ops_registered(void)
-{
-	struct ftrace_ops *op;
-
-	do_for_each_ftrace_op(op, ftrace_ops_list) {
-		if (op->flags & FTRACE_OPS_FL_PERMANENT)
-			return true;
-	} while_for_each_ftrace_op(op);
-
-	return false;
-}
-
 static int
 ftrace_enable_sysctl(const struct ctl_table *table, int write,
 		     void *buffer, size_t *lenp, loff_t *ppos)
@@ -9428,15 +9400,12 @@ ftrace_enable_sysctl(const struct ctl_table *table, int write,
 		ftrace_startup_sysctl();
 
 	} else {
-		if (is_permanent_ops_registered()) {
-			ftrace_enabled = true;
-			return -EBUSY;
-		}
-
-		/* stopping ftrace calls (just send to ftrace_stub) */
-		ftrace_trace_function = ftrace_stub;
-
-		ftrace_shutdown_sysctl();
+		/*
+		 * Disabling ftrace at runtime via this knob is deprecated.
+		 */
+		ftrace_enabled = true;
+		pr_warn_once("The ftrace_enabled file is deprecated and no longer disables ftrace\n");
+		return -EOPNOTSUPP;
 	}
 
 	last_ftrace_enabled = !!ftrace_enabled;
-- 
2.53.0

[for-next][PATCH 2/2] selftests/livepatch: update test-ftrace.sh for deprecated ftrace_enabled

[Steven Rostedt]

From: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>

kernel.ftrace_enabled=0 is now refused on kernels that deprecate the
knob, so the old disable/reload flow no longer applies there. Probe
for this with ftrace_disable_supported() and keep the full original
scenario (disable, fail to load a livepatch, re-enable, load, confirm
disable is refused while loaded) on kernels where it still works;
otherwise just confirm the write is refused.

Link: https://patch.msgid.link/20260806153000.4184871-3-andrey.grodzovsky@crowdstrike.com
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Suggested-by: Joe Lawrence <joe.lawrence@redhat.com>
Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 .../testing/selftests/livepatch/functions.sh  | 14 ++++++
 .../selftests/livepatch/test-ftrace.sh        | 45 ++++++++++++-------
 2 files changed, 42 insertions(+), 17 deletions(-)

diff --git a/tools/testing/selftests/livepatch/functions.sh b/tools/testing/selftests/livepatch/functions.sh
index 30dc677b2f45..a65b7b1ac8ad 100644
--- a/tools/testing/selftests/livepatch/functions.sh
+++ b/tools/testing/selftests/livepatch/functions.sh
@@ -126,6 +126,20 @@ function set_ftrace_enabled() {
 	echo "livepatch: kernel.ftrace_enabled = $result" > /dev/kmsg
 }
 
+# ftrace_disable_supported() - probe whether kernel.ftrace_enabled=0
+#	can still disable ftrace on this kernel. Newer kernels deprecate
+#	the knob and always refuse the write with -EOPNOTSUPP.
+function ftrace_disable_supported() {
+	local orig result
+
+	orig=$(sysctl --values kernel.ftrace_enabled)
+	sysctl -q kernel.ftrace_enabled=0 &> /dev/null
+	result=$(sysctl --values kernel.ftrace_enabled)
+	sysctl -q "kernel.ftrace_enabled=$orig" &> /dev/null
+
+	[[ "$result" == "0" ]]
+}
+
 function cleanup() {
 	pop_config
 }
diff --git a/tools/testing/selftests/livepatch/test-ftrace.sh b/tools/testing/selftests/livepatch/test-ftrace.sh
index d2c3dea63104..cd27148510f8 100755
--- a/tools/testing/selftests/livepatch/test-ftrace.sh
+++ b/tools/testing/selftests/livepatch/test-ftrace.sh
@@ -12,29 +12,32 @@ setup_config
 # - turn ftrace_enabled OFF and verify livepatches can't load
 # - turn ftrace_enabled ON and verify livepatch can load
 # - verify that ftrace_enabled can't be turned OFF while a livepatch is loaded
+# (skipped on kernels where the sysctl is deprecated and always refuses 0)
 
 start_test "livepatch interaction with ftrace_enabled sysctl"
 
-set_ftrace_enabled 0
-load_failing_mod $MOD_LIVEPATCH
+if ftrace_disable_supported; then
 
-set_ftrace_enabled 1
-load_lp $MOD_LIVEPATCH
-if [[ "$(cat /proc/cmdline)" != "$MOD_LIVEPATCH: this has been live patched" ]] ; then
-	echo -e "FAIL\n\n"
-	die "livepatch kselftest(s) failed"
-fi
+	set_ftrace_enabled 0
+	load_failing_mod $MOD_LIVEPATCH
 
-# Check that ftrace could not get disabled when a livepatch is enabled
-set_ftrace_enabled --fail 0
-if [[ "$(cat /proc/cmdline)" != "$MOD_LIVEPATCH: this has been live patched" ]] ; then
-	echo -e "FAIL\n\n"
-	die "livepatch kselftest(s) failed"
-fi
-disable_lp $MOD_LIVEPATCH
-unload_lp $MOD_LIVEPATCH
+	set_ftrace_enabled 1
+	load_lp $MOD_LIVEPATCH
+	if [[ "$(cat /proc/cmdline)" != "$MOD_LIVEPATCH: this has been live patched" ]] ; then
+		echo -e "FAIL\n\n"
+		die "livepatch kselftest(s) failed"
+	fi
 
-check_result "livepatch: kernel.ftrace_enabled = 0
+	# Check that ftrace could not get disabled when a livepatch is enabled
+	set_ftrace_enabled --fail 0
+	if [[ "$(cat /proc/cmdline)" != "$MOD_LIVEPATCH: this has been live patched" ]] ; then
+		echo -e "FAIL\n\n"
+		die "livepatch kselftest(s) failed"
+	fi
+	disable_lp $MOD_LIVEPATCH
+	unload_lp $MOD_LIVEPATCH
+
+	check_result "livepatch: kernel.ftrace_enabled = 0
 % insmod test_modules/$MOD_LIVEPATCH.ko
 livepatch: enabling patch '$MOD_LIVEPATCH'
 livepatch: '$MOD_LIVEPATCH': initializing patching transition
@@ -60,6 +63,14 @@ livepatch: '$MOD_LIVEPATCH': completing unpatching transition
 livepatch: '$MOD_LIVEPATCH': unpatching complete
 % rmmod $MOD_LIVEPATCH"
 
+else
+
+	set_ftrace_enabled --fail 0
+	check_result "livepatch: sysctl: setting key \"kernel.ftrace_enabled\": \
+Operation not supported"
+
+fi
+
 
 # - verify livepatch can load
 # - check if traces have a patched function
-- 
2.53.0