linux-kernel - Re: [patch 1/8] Kprobes - do not use kprobes mutex in arch code

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Message-ID: <20070714192002.GK6975@Krystal>
Date:	Sat, 14 Jul 2007 15:20:02 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Christoph Hellwig <hch@...radead.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, prasanna@...ibm.com,
	ananth@...ibm.com, anil.s.keshavamurthy@...el.com,
	davem@...emloft.net
Subject: Re: [patch 1/8] Kprobes - do not use kprobes mutex in arch code

* Christoph Hellwig (hch@...radead.org) wrote:
> On Fri, Jul 13, 2007 at 09:21:34PM -0400, Mathieu Desnoyers wrote:
> > Remove the kprobes mutex from kprobes.h, since it does not belong there. Also
> > remove all use of this mutex in the architecture specific code, replacing it by
> > a proper mutex lock/unlock in the architecture agnostic code.
> 
> This is not very nice for avr32/sparc64 which have a noop arch_remove_kprobe
> and now need to take a mutex to do nothing.  Maybe you can find a nice
> way to avoid that?
> 
> Except for this issue making kprobes_mutex static to kprobes.c sounds like
> a good improvement.
> 

Since only unregister_kprobe() calls arch_remove_kprobe(), and only
after having removed the struct kprobe from the kprobes list (while the
kprobes mutex is held), I wonder if there is any need to hold the
kprobes mutex at all when calling arch_remove_kprobe(). It turns out
that only get_insn_slot()/free_insn_slot() (which is in
kernel/kprobes.c, but called from arch specific code) seems to really
use protection of this mutex.

Would it make sense to protect the kprobe_insn_pages list with a
new kprobe_insn_mutex, nestable in the kprobe_mutex ?

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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