linux-kernel - Re: [PATCH 2/2] Rewrite jump_label.c to use binary search

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Date:	Wed, 22 Sep 2010 13:57:33 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Andi Kleen <andi@...stfloor.org>, jbaron@...hat.com,
	rostedt@...dmis.com, 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 2/2] Rewrite jump_label.c to use binary search

On Wed, Sep 22, 2010 at 07:31:14AM -0400, Mathieu Desnoyers wrote:
> > -static struct jump_label_entry *add_jump_label_entry(jump_label_t key, int nr_entries, struct jump_entry *table)
> > +void patch_jump_table(unsigned long key, enum jump_label_type type,
> > +	 	      struct jump_entry *start, struct jump_entry *stop)
> >  {
> > -	struct hlist_head *head;
> > -	struct jump_label_entry *e;
> > -	u32 hash;
> > -
> > -	e = get_jump_label_entry(key);
> > -	if (e)
> > -		return ERR_PTR(-EEXIST);
> > -
> > -	e = kmalloc(sizeof(struct jump_label_entry), GFP_KERNEL);
> > -	if (!e)
> > -		return ERR_PTR(-ENOMEM);
> > -
> > -	hash = jhash((void *)&key, sizeof(jump_label_t), 0);
> > -	head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
> > -	e->key = key;
> > -	e->table = table;
> > -	e->nr_entries = nr_entries;
> > -	INIT_HLIST_HEAD(&(e->modules));
> > -	hlist_add_head(&e->hlist, head);
> > -	return e;
> > +	struct jump_entry *entry = search_jump_table(start, stop, key);
> > +	if (!entry)
> > +		return;
> > +	while (entry > start && entry[-1].key == key)
> > +		entry--;
> 
> OK, I like the way it handles patching of multiple entries with the same
> key at once. Sorting really makes sense here.
> 
> > +	for (; entry < stop && entry->key == key; entry++)
> > +		if (kernel_text_address(entry->code))
> 
> This does not work for modules I'm afraid, only for the core kernel. You
> should test for __module_text_address() somewhere.



No, look:

int kernel_text_address(unsigned long addr)
{
	if (core_kernel_text(addr))
		return 1;
	return is_module_text_address(addr);
}


 
> Dumb question: why do you need this test at all ?


I wonder about that too.

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