From 22a97e295ebda1e19daffccce16e6e2aeaf09db1 Mon Sep 17 00:00:00 2001 From: Huiwen He Date: Wed, 18 Mar 2026 07:42:11 -0400 Subject: [PATCH] tracing: Fix syscall events activation by ensuring refcount hits zero [ Upstream commit 0a663b764dbdf135a126284f454c9f01f95a87d4 ] When multiple syscall events are specified in the kernel command line (e.g., trace_event=syscalls:sys_enter_openat,syscalls:sys_enter_close), they are often not captured after boot, even though they appear enabled in the tracing/set_event file. The issue stems from how syscall events are initialized. Syscall tracepoints require the global reference count (sys_tracepoint_refcount) to transition from 0 to 1 to trigger the registration of the syscall work (TIF_SYSCALL_TRACEPOINT) for tasks, including the init process (pid 1). The current implementation of early_enable_events() with disable_first=true used an interleaved sequence of "Disable A -> Enable A -> Disable B -> Enable B". If multiple syscalls are enabled, the refcount never drops to zero, preventing the 0->1 transition that triggers actual registration. Fix this by splitting early_enable_events() into two distinct phases: 1. Disable all events specified in the buffer. 2. Enable all events specified in the buffer. This ensures the refcount hits zero before re-enabling, allowing syscall events to be properly activated during early boot. The code is also refactored to use a helper function to avoid logic duplication between the disable and enable phases. Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Link: https://patch.msgid.link/20260224023544.1250787-1-hehuiwen@kylinos.cn Fixes: ce1039bd3a89 ("tracing: Fix enabling of syscall events on the command line") Signed-off-by: Huiwen He Signed-off-by: Steven Rostedt (Google) Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace_events.c | 51 ++++++++++++++++++++++++++----------- 1 file changed, 36 insertions(+), 15 deletions(-) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index da4a69e1929c..b85045161562 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -3393,27 +3393,23 @@ static __init int event_trace_memsetup(void) return 0; } -static __init void -early_enable_events(struct trace_array *tr, bool disable_first) +/* + * Helper function to enable or disable a comma-separated list of events + * from the bootup buffer. + */ +static __init void __early_set_events(struct trace_array *tr, bool enable) { char *buf = bootup_event_buf; char *token; - int ret; - - while (true) { - token = strsep(&buf, ","); - - if (!token) - break; + while ((token = strsep(&buf, ","))) { if (*token) { - /* Restarting syscalls requires that we stop them first */ - if (disable_first) + if (enable) { + if (ftrace_set_clr_event(tr, token, 1)) + pr_warn("Failed to enable trace event: %s\n", token); + } else { ftrace_set_clr_event(tr, token, 0); - - ret = ftrace_set_clr_event(tr, token, 1); - if (ret) - pr_warn("Failed to enable trace event: %s\n", token); + } } /* Put back the comma to allow this to be called again */ @@ -3422,6 +3418,31 @@ early_enable_events(struct trace_array *tr, bool disable_first) } } +/** + * early_enable_events - enable events from the bootup buffer + * @tr: The trace array to enable the events in + * @disable_first: If true, disable all events before enabling them + * + * This function enables events from the bootup buffer. If @disable_first + * is true, it will first disable all events in the buffer before enabling + * them. + * + * For syscall events, which rely on a global refcount to register the + * SYSCALL_WORK_SYSCALL_TRACEPOINT flag (especially for pid 1), we must + * ensure the refcount hits zero before re-enabling them. A simple + * "disable then enable" per-event is not enough if multiple syscalls are + * used, as the refcount will stay above zero. Thus, we need a two-phase + * approach: disable all, then enable all. + */ +static __init void +early_enable_events(struct trace_array *tr, bool disable_first) +{ + if (disable_first) + __early_set_events(tr, false); + + __early_set_events(tr, true); +} + static __init int event_trace_enable(void) { struct trace_array *tr = top_trace_array();