tracing: syscall_regfunc() should not skip kernel threads

syscall_regfunc() ignores the kernel threads because "it has no effect",
see cc3b13c1 "Don't trace kernel thread syscalls" which added this check.

However, this means that a user-space task spawned by call_usermodehelper()
will run without TIF_SYSCALL_TRACEPOINT if sys_tracepoint_refcount != 0.

Remove this check. The unnecessary report from ret_from_fork path mentioned
by cc3b13c1 is no longer possible, see See commit fb45550d76bb5 "make sure
that kernel_thread() callbacks call do_exit() themselves".

A kernel_thread() callback can only return and take the int_ret_from_sys_call
path after do_execve() succeeds, otherwise the kernel will crash. But in this
case it is no longer a kernel thread and thus is needs TIF_SYSCALL_TRACEPOINT.

Link: http://lkml.kernel.org/p/20140413185938.GD20668@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 9cf12640de5a98dd16eee26cd69dc60a2367049a..3490407dc7b7fefc697b8284375ab315c1df02f0 100644 (file)
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -497,9 +497,7 @@ void syscall_regfunc(void)
        if (!sys_tracepoint_refcount) {
                read_lock(&tasklist_lock);
                for_each_process_thread(p, t) {
-                       /* Skip kernel threads. */
-                       if (!(t->flags & PF_KTHREAD))
-                               set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
+                       set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
                }
                read_unlock(&tasklist_lock);
        }