On 6/27/06, Paul Fulghum <[email protected]> wrote:
No one has leaped in here with any wisdom, but the people
who wrote that code may be dead or otherwise employed.
If you have knowledge of how those bits work,
I encourage to you dig through the code and determine
what needs to be done. It is certainly an area that can
use more review.
I did see a comment that tty_mutex protects the creation
and destruction of tty structures, so I assume the coverage
of tty_old_pgrp has some relation to that. Unfortunately,
I have seen other locks get borrowed for multiple purposes.
I'm having trouble divining the use of tty_mutex. In most cases it is
protecting pgrp, tty_old_pgrp and tty fields in signal_struct.
sys_setsid(), disassociate_ctty(), daemonize(), tty::release_dev(),
tty_open() use it this way. But it is also used to protect
tty::init_dev() which makes no use of the signal_struct fields. Then
there is the use in vt::con_close() which also does not involved the
signal_struct fields.
Why does this need to be protected? exit.c
mutex_lock(&tty_mutex);
current->signal->tty = NULL;
mutex_unlock(&tty_mutex);
After looking at all of this for a couple of hours it looks to me like
tty_mutex could be removed if ref counts were used to control when the
tty_struct gets destroyed. I think the problem being addressed is
dangling pointers in signal_struct::tty when a tty is being closed.
Ref counts would delay the freeing of tty_struct until all the
references were released.
--
Jon Smirl
[email protected]
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