Messages in this thread Patch in this message | | | From | Michael Ellerman <> | Subject | [PATCH] tracing: Allow raw_syscall tracepoints to work from boot | Date | Wed, 14 Jan 2015 09:35:17 +1100 |
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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 <mpe@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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