linux-kernel - Re: [PATCH 1/2] Add for_each

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Date:	Wed, 22 Sep 2010 16:50:13 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	jbaron@...hat.com, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, hpa@...or.com,
	tglx@...utronix.de, roland@...hat.com, rth@...hat.com,
	mhiramat@...hat.com, avi@...hat.com, davem@...emloft.net,
	vgoyal@...hat.com, sam@...nborg.org, tony@...eyournoodle.com,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] Add for_each_module iterator function v2

On Wed, Sep 22, 2010 at 04:35:15PM +0200, Andi Kleen wrote:
> On Wed, Sep 22, 2010 at 10:14:32AM -0400, Mathieu Desnoyers wrote:
> > * Andi Kleen (andi@...stfloor.org) wrote:
> > > From: Andi Kleen <ak@...ux.intel.com>
> > > 
> > > This is a generic function to iterate over all modules.
> > > To be used in the next patch.
> > > 
> > > v2: Use module_mutex instead of preempt disabling
> > > 
> > > Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> > > ---
> > >  include/linux/module.h |    1 +
> > >  kernel/module.c        |   10 ++++++++++
> > >  2 files changed, 11 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/include/linux/module.h b/include/linux/module.h
> > > index 403ac26..809b6db 100644
> > > --- a/include/linux/module.h
> > > +++ b/include/linux/module.h
> > > @@ -410,6 +410,7 @@ struct module *__module_address(unsigned long addr);
> > >  bool is_module_address(unsigned long addr);
> > >  bool is_module_percpu_address(unsigned long addr);
> > >  bool is_module_text_address(unsigned long addr);
> > > +void for_each_module(void (*op)(struct module *, void *arg), void *arg);
> > >  
> > >  static inline int within_module_core(unsigned long addr, struct module *mod)
> > >  {
> > > diff --git a/kernel/module.c b/kernel/module.c
> > > index eba1341..9e2a561 100644
> > > --- a/kernel/module.c
> > > +++ b/kernel/module.c
> > > @@ -384,6 +384,16 @@ struct module *find_module(const char *name)
> > >  }
> > >  EXPORT_SYMBOL_GPL(find_module);
> > >  
> > > +void for_each_module(void (*op)(struct module *, void *arg), void *arg)
> > > +{
> > > +	struct module *mod;
> > > +
> > > +	mutex_lock(&module_mutex);
> > 
> > I'm concerned about the following mutex dependency chain:
> > 
> > module_mutex -> jump_label_mutex (on module load)
> > jump_label_mutex -> module_mutex (on jump_label_update)
> 
> There are actually more problems in this version with using
> module_mutex().  Looking at a fix.
> 
> > 
> > Actually, I think your module notifier is missing in your version. This
> > is why you don't see this dependency problem.
> 
> The module notifier is not needed anymore, but there's another 
> callback through the trace point code on module load.
> 
> Unload notifier is not needed anymore because there is no
> state to tear down.
> 
> -Andi


If possible, could you please also join a git url with your next version,
it becomes hard to review as it's delta on top of others patches.

Thanks.

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