Re: [RFC PATCH v2] posix-timers: Support delivery of signals to the current thread

Oleg Nesterov
2023-01-25T17:10:24Z

On 01/25, Oleg Nesterov wrote:
>
> > > int posix_timer_event(struct k_itimer *timr, int si_private)
> > > {
> > > enum pid_type type;
> > > + struct pid *pid;
> > > int ret;
> > > /*
> > > * FIXME: if ->sigq is queued we can race with
> > > @@ -350,8 +351,9 @@ int posix_timer_event(struct k_itimer *timr, int si_private)
> > > */
> > > timr->sigq->info.si_sys_private = si_private;
> > >
> > > - type = !(timr->it_sigev_notify & SIGEV_THREAD_ID) ? PIDTYPE_TGID : PIDTYPE_PID;
> > > - ret = send_sigqueue(timr->sigq, timr->it_pid, type);
> > > + type = (timr->it_sigev_notify & SIGEV_THREAD_ID) ? PIDTYPE_PID : PIDTYPE_TGID;
> > > + pid = (type == PIDTYPE_PID) ? timr->it_pid : task_pid(current);
> > > + ret = send_sigqueue(timr->sigq, pid, type);
> > > /* If we failed to send the signal the timer stops. */
> > > return ret > 0;
> > > }

...

> But! I just noticed send_sigqueue() does pid_task(pid, type), so the patch
> above needs another change
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1970,7 +1970,8 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
>
> ret = -1;
> rcu_read_lock();
> - t = pid_task(pid, type);
> + // comment to explain why don't we use "type"
> + t = pid_task(pid, PIDTYPE_PID);
> if (!t || !likely(lock_task_sighand(t, &flags)))
> goto ret;

So. Unless I missed something (quite possibly) we do not even need the patch
above. The one liner change below can work just fine.

Oleg.

--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1970,7 +1970,8 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)

ret = -1;
rcu_read_lock();
- t = pid_task(pid, type);
+ /* GOOD COMMENT */
+ t = type == PIDTYPE_PID ? pid_task(pid, type) : current;
if (!t || !likely(lock_task_sighand(t, &flags)))
goto ret;