Re: [PATCH] console close race fix resend

[Robert Love <rml@tech9.net>]

On Mon, 2001-12-10 at 22:16, Gordon Oliver wrote:

> and (c) appears to still have a race... You should extract
> the value from the structure inside the lock, otherwise you
> will still race with con_close (though perhaps a smaller race)
> but since the call to acquire_console_sem() can sleep, the
> vt handle you have may be stale.

Ehh, I don't think so.  Here is the whole patched function:

static void con_flush_chars(struct tty_struct *tty)
{
	struct vt_struct *vt = (struct vt_struct *)tty->driver_data;
	if (in_interrupt())	/* from flush_to_ldisc */
		return;
	pm_access(pm_con);
	acquire_console_sem();
	if (vt)
		set_cursor(vt->vc_num);
	release_console_sem();
}

When we check vt, it isn't stale.  vt is a _pointer_ to the data so that
first reference against it is guaranteed to grab the correct value.  The
only possible race is between the if and the set_cursor, but that isn't
an issue because we acquired the console semaphore.  There is no race
here.

> > Please, for all that is righteous, apply.
> 
> please fix it better first...
> (unless I am mistaken).

Thus, unless I am mistaken, it is fine.  Please, apply.

	Robert Love