In commit 5f893b2639b2 "tracing: Move enabling tracepoints to just after
rcu_init()", tracing was enabled earlier in boot.
This broke tracing of the raw_syscall tracepoints from boot using the
trace_event kernel parameter.
When the registration function for the raw_syscall tracepoints runs, it
iterates over all tasks setting TIF_SYSCALL_TRACEPOINT. However now that
this happens earlier in boot, the loop has no effect because there are
no tasks in existence other than init_task, which is skipped by the
for_each_process_thread() macro.
We can fix it by explicitly setting TIF_SYSCALL_TRACEPOINT for the
init_task. That way when pid 1 is cloned from init_task it will inherit
TIF_SYSCALL_TRACEPOINT.
Fixes: 5f893b2639b2 ("tracing: Move enabling tracepoints to just after
rcu_init()")
Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
---
kernel/tracepoint.c | 6 ++++++
1 file changed, 6 insertions(+)
It feels a bit naughty to be whacking init_task like this, but it also
seems like the right fix?
Should we also clear it in the unregfunc? I can't see how that would
ever be needed in practice?
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 3490407dc7b7..43a03e22c16c 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -496,6 +496,12 @@ void syscall_regfunc(void)
if (!sys_tracepoint_refcount) {
read_lock(&tasklist_lock);
+ /*
+ * If we run very early in boot then we need to hit init_task
+ * directly so that pid 1 will inherit the TIF flag.
+ */
+ set_tsk_thread_flag(&init_task, TIF_SYSCALL_TRACEPOINT);
+
for_each_process_thread(p, t) {
set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
}
--
2.1.0
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