On 03/20, Oleg Nesterov wrote:
>
> On 03/19, Davide Libenzi wrote:
> >
> > I'd need a get_task_struct in any case in order to safely call
> > unlock_task_sighand(). At that point I'd prefer to just pass through the
> > struct pid*. I'll be posting the new version for review as soon as I
> > complete a few tests ...
>
> If signalfd_get_sighand()->lock_task_sighand() succeeds, it is safe to
> dereference ctx->tsk. The task can't be freed and ctx->tsk can't be cleared
> while we are holding siglock.
>
> However, I was wrong, we still need a re-check after lock_task_sighand().
> We should check ctx->tsk != NULL.
IOW, we can (afaics) do
static struct sighand_struct *signalfd_get_sighand(struct signalfd_ctx
*ctx,
unsigned long *flags)
{
struct sighand_struct *sighand = NULL;
struct tsak_struct *tsk;
rcu_read_lock();
tsk = rcu_dereference(ctx->tsk); // not needed, just a
documentation
if (tsk != NULL)
sighand = lock_task_sighand(tsk, flags);
rcu_read_unlock();
if (sighand && !ctx->tsk)) {
unlock_task_sighand(tsk, flags);
sighand = NULL;
}
return sighand;
}
If signalfd_get_sighand() succeeds, ctx->tsk is pinned.
Oleg.
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