Paul E. McKenney wrote:
>
> On Wed, Aug 17, 2005 at 06:35:03PM +0400, Oleg Nesterov wrote:
> >
> > Sorry, I don't understand you. CLONE_THREAD implies CLONE_SIGHAND,
> > so we always need to lock one ->sighand. Could you please clarify?
>
> On the #3 and #4 code paths, the code assumes that the task-list lock
> is held. So I was thinking of something (very roughly) as follows:
>
> #define SIGLOCK_HOLD_RCU (1 << 0)
> #define SIGLOCK_HOLD_TASKLIST (1 << 1)
> #define SIGLOCK_HOLD_SIGLOCK (1 << 2)
Oh, no, sorry for confusion.
I meant this function should only lock ->sighand, nothing more, something
like this:
// must be called with preemtion disabled !!!
struct sighand_struct *lock_task_sighand(struct task_struct *tsk, unsigned long
*flags)
{
struct sighand_struct *sighand;
// sighand = NULL;
// if (!get_task_struct_rcu(tsk))
// goto out;
for (;;) {
sighand = tsk->sighand;
if (unlikely(sighand == NULL))
break;
spin_lock_irqsave(sighand->siglock, *flags);
if (likely(sighand == tsk->sighand)
goto out;
spin_unlock_irqrestore(sighand->siglock, *flags);
}
// put_task_struct(tsk);
out:
return sighand;
}
static inline void unlock_task_sighand(struct task_struct *tsk, unsigned long
*flags)
{
spin_unlock_irqrestore(tsk->sighand->siglock, flags);
// put_task_struct(tsk);
}
int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
{
unsigned long flags;
int ret;
ret = check_kill_permission(sig, info, p);
if (!ret && sig) {
ret = -ESRCH;
if (lock_task_sighand(p, &flags)) {
ret = __group_send_sig_info(sig, info, p);
unlock_task_sighand(p, &flags);
}
}
return ret;
}
Currently the only user of it will be group_send_sig_info(), but I hope
you have devil plans to kill the "tasklist_lock guards the very rare
->sighand change" finally :)
Oleg.
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