On 07/31, Peter Zijlstra wrote:
>
> In order to direct the SIGIO signal to a particular thread of a
> multi-threaded application we cannot, like suggested by the manpage, put
> a TID into the regular fcntl(F_SETOWN) call. It will still be send to
> the whole process of which that thread is part.
>
> Since people do want to properly direct SIGIO we introduce F_SETOWN_TID,
> which functions similarly to F_SETOWN, except positive arguments are
> interpreted as TIDs and negative arguments are interpreted as PIDs.
I think this is correct. But,
> @@ -431,6 +474,7 @@ static void send_sigio_to_task(struct task_struct *p,
> int fd,
> int reason)
> {
> + int (*send_sig)(int, struct siginfo *, struct task_struct *);
> /*
> * F_SETSIG can change ->signum lockless in parallel, make
> * sure we read it once and use the same value throughout.
> @@ -440,6 +484,8 @@ static void send_sigio_to_task(struct task_struct *p,
> if (!sigio_perm(p, fown, signum))
> return;
>
> + send_sig = fown->task_only ? send_sig_info : group_send_sig_info;
this is ugly.
I do not blame your patch, I blame signal.c which has a lot of helpers
to send a signal but it is never possible to find the right one.
I think we need a new trivial helper,
int xxx(int sig, struct siginfo *info, struct task_struct *p, bool
group)
{
unsigned long flags;
int ret = -ESRCH;
if (lock_task_sighand(p, &flags)) {
ret = send_signal(sig, info, p, group);
unlock_task_sighand(p, &flags);
}
return ret;
}
send_sigio_to_task() can just do: send_signal(..., !fown->task_only).
group_send_sig_info(), send_sig_info() should use this helper too.
Also. without the new helper, F_SETOWN does check_kill_permission()
while F_SETOWN_TID does not. This doesn't really matter, but this
looks a bit odd.
Note that send_sigio_to_task() does not need check_kill_permission().
We use either SEND_SIG_PRIV or SI_FROMKERNEL() signals, so we never
actually check permissions. Even if we did, it would be just wrong
to deny the signal here using current_cred().
Peter, may I suggest to to re-diff your patch on top of the trivial
patch I am going to send a bit later today?
Oleg.
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