FAILED: patch "[PATCH] tracepoint: balance regfunc() on func_add() failure in" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] tracepoint: balance regfunc() on func_add() failure in" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x fad217e16fded7f3c09f8637b0f6a224d58b5f2e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026050737-recoil-baritone-4e0e@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From fad217e16fded7f3c09f8637b0f6a224d58b5f2e Mon Sep 17 00:00:00 2001
From: David Carlier <devnexen@gmail.com>
Date: Mon, 13 Apr 2026 20:06:01 +0100
Subject: [PATCH] tracepoint: balance regfunc() on func_add() failure in
 tracepoint_add_func()

When a tracepoint goes through the 0 -> 1 transition, tracepoint_add_func()
invokes the subsystem's ext->regfunc() before attempting to install the
new probe via func_add(). If func_add() then fails (for example, when
allocate_probes() cannot allocate a new probe array under memory pressure
and returns -ENOMEM), the function returns the error without calling the
matching ext->unregfunc(), leaving the side effects of regfunc() behind
with no installed probe to justify them.

For syscall tracepoints this is particularly unpleasant: syscall_regfunc()
bumps sys_tracepoint_refcount and sets SYSCALL_TRACEPOINT on every task.
After a leaked failure, the refcount is stuck at a non-zero value with no
consumer, and every task continues paying the syscall trace entry/exit
overhead until reboot. Other subsystems providing regfunc()/unregfunc()
pairs exhibit similarly scoped persistent state.

Mirror the existing 1 -> 0 cleanup and call ext->unregfunc() in the
func_add() error path, gated on the same condition used there so the
unwind is symmetric with the registration.

Fixes: 8cf868affdc4 ("tracing: Have the reg function allow to fail")
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260413190601.21993-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 91905aa19294..dffef52a807b 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -300,6 +300,8 @@ static int tracepoint_add_func(struct tracepoint *tp,
 			lockdep_is_held(&tracepoints_mutex));
 	old = func_add(&tp_funcs, func, prio);
 	if (IS_ERR(old)) {
+		if (tp->ext && tp->ext->unregfunc && !static_key_enabled(&tp->key))
+			tp->ext->unregfunc();
 		WARN_ON_ONCE(warn && PTR_ERR(old) != -ENOMEM);
 		return PTR_ERR(old);
 	}

[PATCH 5.15.y] tracepoint: balance regfunc() on func_add() failure in tracepoint_add_func()

[Sasha Levin]

From: David Carlier <devnexen@gmail.com>

[ Upstream commit fad217e16fded7f3c09f8637b0f6a224d58b5f2e ]

When a tracepoint goes through the 0 -> 1 transition, tracepoint_add_func()
invokes the subsystem's ext->regfunc() before attempting to install the
new probe via func_add(). If func_add() then fails (for example, when
allocate_probes() cannot allocate a new probe array under memory pressure
and returns -ENOMEM), the function returns the error without calling the
matching ext->unregfunc(), leaving the side effects of regfunc() behind
with no installed probe to justify them.

For syscall tracepoints this is particularly unpleasant: syscall_regfunc()
bumps sys_tracepoint_refcount and sets SYSCALL_TRACEPOINT on every task.
After a leaked failure, the refcount is stuck at a non-zero value with no
consumer, and every task continues paying the syscall trace entry/exit
overhead until reboot. Other subsystems providing regfunc()/unregfunc()
pairs exhibit similarly scoped persistent state.

Mirror the existing 1 -> 0 cleanup and call ext->unregfunc() in the
func_add() error path, gated on the same condition used there so the
unwind is symmetric with the registration.

Fixes: 8cf868affdc4 ("tracing: Have the reg function allow to fail")
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260413190601.21993-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
[ changed `tp->ext->unregfunc` to `tp->unregfunc` to match older struct layout ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/tracepoint.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 64ea283f2f86d..38e83507e6fd1 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -337,6 +337,8 @@ static int tracepoint_add_func(struct tracepoint *tp,
 			lockdep_is_held(&tracepoints_mutex));
 	old = func_add(&tp_funcs, func, prio);
 	if (IS_ERR(old)) {
+		if (tp->unregfunc && !static_key_enabled(&tp->key))
+			tp->unregfunc();
 		WARN_ON_ONCE(warn && PTR_ERR(old) != -ENOMEM);
 		return PTR_ERR(old);
 	}
-- 
2.53.0