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Date: Thu, 16 Jul 2020 13:48:20 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Allen Pais <allen.lkml@...il.com>, 
	Oscar Carter <oscar.carter@....com>, Romain Perier <romain.perier@...il.com>, 
	Kevin Curtis <kevin.curtis@...site.co.uk>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Harald Freudenberger <freude@...ux.ibm.com>, 
	Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, 
	Christian Borntraeger <borntraeger@...ibm.com>, Jiri Slaby <jslaby@...e.com>, 
	Felipe Balbi <balbi@...nel.org>, Jason Wessel <jason.wessel@...driver.com>, 
	Daniel Thompson <daniel.thompson@...aro.org>, Douglas Anderson <dianders@...omium.org>, 
	Mitchell Blank Jr <mitch@...oth.com>, Julian Wiedmann <jwi@...ux.ibm.com>, 
	Karsten Graul <kgraul@...ux.ibm.com>, Ursula Braun <ubraun@...ux.ibm.com>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, 
	Christian Gromm <christian.gromm@...rochip.com>, Nishka Dasgupta <nishkadg.linux@...il.com>, 
	Masahiro Yamada <masahiroy@...nel.org>, Stephen Boyd <swboyd@...omium.org>, 
	"Matthew Wilcox (Oracle)" <willy@...radead.org>, Wambui Karuga <wambui.karugax@...il.com>, 
	Guenter Roeck <linux@...ck-us.net>, Chris Packham <chris.packham@...iedtelesis.co.nz>, 
	Kyungtae Kim <kt0755@...il.com>, 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, 
	Jonathan Corbet <corbet@....net>, Will Deacon <will@...nel.org>, 
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>, 
	netdev <netdev@...r.kernel.org>, linux-s390@...r.kernel.org, 
	devel@...verdev.osuosl.org, USB list <linux-usb@...r.kernel.org>, 
	kgdb-bugreport@...ts.sourceforge.net, 
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 0/3] Modernize tasklet callback API

On Thu, Jul 16, 2020 at 12:14 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Jul 16, 2020 at 09:57:18AM +0200, Peter Zijlstra wrote:
> > On Wed, Jul 15, 2020 at 08:08:44PM -0700, Kees Cook wrote:
> > > Hi,
> > >
> > > This is the infrastructure changes to prepare the tasklet API for
> > > conversion to passing the tasklet struct as the callback argument instead
> > > of an arbitrary unsigned long. The first patch details why this is useful
> > > (it's the same rationale as the timer_struct changes from a bit ago:
> > > less abuse during memory corruption attacks, more in line with existing
> > > ways of doing things in the kernel, save a little space in struct,
> > > etc). Notably, the existing tasklet API use is much less messy, so there
> > > is less to clean up.
> >
> > I would _MUCH_ rather see tasklets go the way of the dodo, esp. given
> > that:
> >
> > >  drivers/input/keyboard/omap-keypad.c   |  2 +-
> > >  drivers/input/serio/hil_mlc.c          |  2 +-
> > >  drivers/net/wan/farsync.c              |  4 +--
> > >  drivers/s390/crypto/ap_bus.c           |  2 +-
> > >  drivers/staging/most/dim2/dim2.c       |  2 +-
> > >  drivers/staging/octeon/ethernet-tx.c   |  2 +-
> > >  drivers/tty/vt/keyboard.c              |  2 +-
> > >  drivers/usb/gadget/udc/snps_udc_core.c |  6 ++---
> > >  drivers/usb/host/fhci-sched.c          |  2 +-
> > >  include/linux/interrupt.h              | 37 ++++++++++++++++++++++----
> > >  kernel/backtracetest.c                 |  2 +-
> > >  kernel/debug/debug_core.c              |  2 +-
> > >  kernel/irq/resend.c                    |  2 +-
> > >  kernel/softirq.c                       | 18 ++++++++++++-
> > >  net/atm/pppoatm.c                      |  2 +-
> > >  net/iucv/iucv.c                        |  2 +-
> > >  sound/drivers/pcsp/pcsp_lib.c          |  2 +-
> > >  17 files changed, 66 insertions(+), 25 deletions(-)
> >
> > there appear to be hardly any users left.. Can't we stage an extinction
> > event here instead?
>
> Oh, I wish, but no. That's just the ones using DECLARE_TASKLET. There
> are hundred(s?) more (see the referenced tree).

Still, do we really need tasklets? Can we substitute timers executing
immediately in their place?

Thanks.

-- 
Dmitry

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