On 5/1/05, Andrew Morton <[email protected]> wrote:
> Alan Stern <[email protected]> wrote:
> >
> > On Sun, 1 May 2005, Andrey Borzenkov wrote:
> >
> > > Hub driver is using SIGKILL to terminate khubd. Unfortunately on a number of
> > > distributions switching init levels implicitly does "killall -9", killing
> > > khubd. The only way to restart it is to reload USB subsystem.
> > >
> > > Is signal usage in this case really needed? What about replacing it with
> > > simple flag (i.e. will patch be accepted)?
> >
> > IMO the problem lies in those distributions. They should not
> > indiscrimately kill processes when switching init levels.
>
> Nevertheless it's better that kernel internals not be exposed to userspace
> actions in this manner, and using signals for in-kernel IPC is crufty, IMO.
>
> It's pretty simple to convert khubd to use the kthread API. Something like
> this (untested):
>
> drivers/usb/core/hub.c | 40 +++++++++++-----------------------------
> 1 files changed, 11 insertions(+), 29 deletions(-)
>
> diff -puN drivers/usb/core/hub.c~hub-use-kthread drivers/usb/core/hub.c
> --- 25/drivers/usb/core/hub.c~hub-use-kthread 2005-05-01 15:22:24.634539928 -0700
> +++ 25-akpm/drivers/usb/core/hub.c 2005-05-01 15:29:55.739961480 -0700
<snip>
> static int hub_thread(void *__unused)
<snip>
> - /* Send me a signal to get me die (for debugging) */
> do {
> hub_events();
> - wait_event_interruptible(khubd_wait, !list_empty(&hub_event_list));
> + wait_event_interruptible(khubd_wait,
> + !list_empty(&hub_event_list) ||
> + kthread_should_stop());
> try_to_freeze(PF_FREEZE);
> - } while (!signal_pending(current));
> + } while (!kthread_should_stop() || !list_empty(&hub_event_list));
Shouldn't this simply be a wait_event(), instead of
wait_event_interruptible()? Then the do-while() can be gotten rid of,
as the only reason it is there currently, I guess, is to ignore
signals?
Also, the while's conditional should be (!kthread_should_stop() ||
list_empty(&hub_event_list) to match the negation of wait_event's?
(wait_event() expects the condition to stop on, while while() expects
the condition to continue on)
Thanks,
Nish
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