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Subjectsyscall_regfunc() && TIF_SYSCALL_TRACEPOINT
Hello.

I've looked at syscall_regfunc/unregfunc by accident, and I am
a bit confused...

void syscall_regfunc(void)
{
unsigned long flags;
struct task_struct *g, *t;

if (!sys_tracepoint_refcount) {
read_lock_irqsave(&tasklist_lock, flags);

Why _irqsave? write_lock(tasklist) needs to disable irqs, but read_
doesn't. Any subtle reason I missed?

do_each_thread(g, t) {
/* Skip kernel threads. */
if (t->mm)

We should check PF_KTHREAD, not ->mm.

set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);

But the main question is, can't we race with clone() and miss the
new child? The new task is not "visible" to do_each_thread() until
copy_process()->list_add_tail_rcu(thread_group/init_task.tasks).

Don't we need something like the patch below?

Oleg.


--- x/kernel/fork.c
+++ x/kernel/fork.c
@@ -1446,7 +1446,12 @@ static struct task_struct *copy_process(

total_forks++;
spin_unlock(&current->sighand->siglock);
+#ifdef CONFIG_TRACEPOINTS
+ if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
+ set_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT);
+#endif
write_unlock_irq(&tasklist_lock);
+
proc_fork_connector(p);
cgroup_post_fork(p);
if (clone_flags & CLONE_THREAD)


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