SIGILL @ pthread_create() after execv

[Daniel Eischen]

On Tue, 21 Sep 2004, Julian Elischer wrote:

>
>
> Daniel Eischen wrote:
>
> >This looks OK to me.
> >
> >
>
> Ok, so what happens if 2 threads call execve() at the same time and the
> first one in fails
> but the second one would succeed?
> By the time we've discovered that the first would have failed, we've
> probably already
> told the second that it was too late.

Well, we can easily stop that in userland by taking a mutex
or lock before the exec() then releasing it if the exec
fails.  Both libthr and libpthread would have to do this,
I think.

> In this case teh second thread has 2 options
> (assuming 2 processors)
> 1/ on dicovering that P_INEXEC is already set, it could just die, (i.e
> release locks it has and call thread_exit().
> 2/ it could sleep on something, knowing that the leading thread will
> wake it up and force it to
> return (and thus call thread_exit() in userret) when it eventually calls
> thread_single()
> after it has passed all the permissions tests.

Probably #2, but you could just disregard this situation if
you want to put the onus on userland.  I think an msleep()
or CV would work if you want to block in the kernel.  If
the exec fails(), you can just wakeup() any waiters.

-- 
Dan Eischen