Re: [PATCH] change kernel threads to ignore signals instead of blocking them

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 13 Apr 2007 11:31:16 +0400 Oleg Nesterov <oleg@tv-sign.ru> wrote:

> On top of Eric's
> 
> 	kthread-dont-depend-on-work-queues-take-2.patch
> 
> Currently kernel threads use sigprocmask(SIG_BLOCK) to protect against signals.
> This doesn't prevent the signal delivery, this only blocks signal_wake_up().
> Every "killall -33 kthreadd" means a "struct siginfo" leak.
> 
> Change kthreadd_setup() to set all handlers to SIG_IGN instead of blocking them
> (make a new helper ignore_signals() for that). If the kernel thread needs some
> signal, it should use allow_signal() anyway, and in that case it should not use
> CLONE_SIGHAND.
> 
> Note that we can't change daemonize() (should die!) in the same way, because
> it can be used along with CLONE_SIGHAND. This means that allow_signal() still
> should unblock the signal to work correctly with daemonize()ed threads.
> 
> However, disallow_signal() doesn't block the signal any longer but ignores it.
> 
> NOTE: with or without this patch the kernel threads are not protected from
> handle_stop_signal(), this seems harmless, but not good.

I'm seeing 500 zombied instances of khelper (from udev startup).  It only
happens when the utrace patches are applied.  Presumably an interaction
between utrace and one of these kthread changes.

I'll drop utrace for now.  I don't think it's getting much help from being
in -mm at present and it's getting increasingly painful to keep it merged
against all the other stuff which is happening.

Roland, I'll squirt all the extra utrace patches which I have in your direction.
Please merge them or hang on to them for later on.