linux-kernel - [PATCH RFC 0/8] jump-label: allow early jump_label

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Date:	Thu, 29 Sep 2011 16:26:30 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	David Daney <david.daney@...ium.com>,
	Michael Ellerman <michael@...erman.id.au>,
	Jan Glauber <jang@...ux.vnet.ibm.com>,
	Jason Baron <jbaron@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: [PATCH RFC 0/8] jump-label: allow early jump_label_enable()

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>

Hi all,

While trying to use the jump-label stuff for my PV ticketlock changes,
I had some problems using jump labels early in the kernel's lifetime
(pre-SMP).

The basic problem is that even if I enable a jump_label_key, the
jump_label_init() initializer ends up nopping out all the code sites.

This series enables early use of jump labels by making
jump_label_init() respect already-enabled keys.

To do this, I've dropped arch_jump_label_poke_text_early() and
replaced it with arch_jump_label_transform_early(), which is the same
as the non-_early variant except that it expects to be operating in a
pre-SMP environment.

I've tested this on x86, but all the other architecture changes are
completely untested (not even breathed on by a compiler).

One big question which arises is whether the _early() function is
necessary at all.  All the stop_machine/mutex/etc stuff that
arch_jump_label_transform() ends up doing is redundant pre-SMP, but it
shouldn't hurt.  Maybe we can just drop the _early function?  It works
on x86, at least, because jump_label_enable() works, which uses the full
form.  And dropping it would reduce this to a very much smaller series.

Thanks,
	J

Jeremy Fitzhardinge (8):
  jump_label: use proper atomic_t initializer
  jump_label: if a key has already been initialized, don't nop it out
  x86/jump_label: add arch_jump_label_transform_early()
  sparc/jump_label: add arch_jump_label_transform_early()
  mips/jump_label: add arch_jump_label_transform_early()
  powerpc/jump_label: add arch_jump_label_transform_early()
  s390/jump-label: add arch_jump_label_transform_early()
  jump_label: drop default arch_jump_label_transform_early

 arch/mips/kernel/jump_label.c    |   21 +++++++++++++---
 arch/powerpc/kernel/jump_label.c |    6 ++++
 arch/s390/kernel/jump_label.c    |   49 +++++++++++++++++++++++--------------
 arch/sparc/kernel/jump_label.c   |   24 +++++++++++-------
 arch/x86/kernel/jump_label.c     |   20 +++++++++++----
 include/linux/jump_label.h       |    7 +++--
 kernel/jump_label.c              |   20 ++++++---------
 7 files changed, 94 insertions(+), 53 deletions(-)

-- 
1.7.6.2

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