From: David Carlier Date: Mon, 13 Apr 2026 19:06:01 +0000 (+0100) Subject: tracepoint: balance regfunc() on func_add() failure in tracepoint_add_func() X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=fad217e16fded7f3c09f8637b0f6a224d58b5f2e;p=thirdparty%2Fkernel%2Flinux.git 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 Cc: Mathieu Desnoyers Link: https://patch.msgid.link/20260413190601.21993-1-devnexen@gmail.com Signed-off-by: David Carlier Signed-off-by: Steven Rostedt (Google) --- diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index 91905aa19294d..dffef52a807bc 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); }