linux-kernel - Re: Re: [PATCH v2 1/4] kprobes: delay blacklist symbol lookup until we actually need it

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Message-ID: <20130405100049.GI2481@caracas.corpusers.net>
Date:	Fri, 5 Apr 2013 12:00:49 +0200
From:	Oskar Andero <oskar.andero@...ymobile.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"anil.s.keshavamurthy@...el.com" <anil.s.keshavamurthy@...el.com>,
	"ananth@...ibm.com" <ananth@...ibm.com>,
	"Lekanovic, Radovan" <Radovan.Lekanovic@...ymobile.com>,
	Davidsson, Björn 
	<Bjorn.Davidsson@...ymobile.com>,
	Toby Collett <toby.collett@...ymobile.com>,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: Re: [PATCH v2 1/4] kprobes: delay blacklist symbol lookup until
 we actually need it

Thanks for your input guys!

On 04:16 Fri 05 Apr     , Masami Hiramatsu wrote:
> (2013/04/05 9:56), Joonsoo Kim wrote:
> > Hello, Oskar.
> > 
> > On Thu, Apr 04, 2013 at 02:51:26PM +0200, Oskar Andero wrote:
> >> From: Toby Collett <toby.collett@...ymobile.com>
> >>
> >> The symbol lookup can take a long time and kprobes is
> >> initialised very early in boot, so delay symbol lookup
> >> until the blacklist is first used.
> >>
> >> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> >> Cc: David S. Miller <davem@...emloft.net>
> >> Reviewed-by: Radovan Lekanovic <radovan.lekanovic@...ymobile.com>
> >> Signed-off-by: Toby Collett <toby.collett@...ymobile.com>
> >> Signed-off-by: Oskar Andero <oskar.andero@...ymobile.com>
> >> ---
> >>  kernel/kprobes.c | 98 ++++++++++++++++++++++++++++++++++----------------------
> >>  1 file changed, 60 insertions(+), 38 deletions(-)
> >>
> >> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> >> index e35be53..0a270e5 100644
> >> --- a/kernel/kprobes.c
> >> +++ b/kernel/kprobes.c
> >> @@ -68,6 +68,7 @@
> >>  #endif
> >>  
> >>  static int kprobes_initialized;
> >> +static int kprobe_blacklist_initialized;
> >>  static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
> >>  static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
> >>  
> >> @@ -102,6 +103,60 @@ static struct kprobe_blackpoint kprobe_blacklist[] = {
> >>  	{NULL}    /* Terminator */
> >>  };
> >>  
> >> +/* it can take some time ( > 100ms ) to initialise the
> >> + * blacklist so we delay this until we actually need it
> >> + */
> >> +static void init_kprobe_blacklist(void)
> >> +{
> >> +	int i;
> >> +	unsigned long offset = 0, size = 0;
> >> +	char *modname, namebuf[128];
> >> +	const char *symbol_name;
> >> +	void *addr;
> >> +	struct kprobe_blackpoint *kb;
> >> +
> >> +	mutex_lock(&kprobe_mutex);
> >> +	if (kprobe_blacklist_initialized)
> >> +		goto out;
> >> +
> >> +	/*
> >> +	 * Lookup and populate the kprobe_blacklist.
> >> +	 *
> >> +	 * Unlike the kretprobe blacklist, we'll need to determine
> >> +	 * the range of addresses that belong to the said functions,
> >> +	 * since a kprobe need not necessarily be at the beginning
> >> +	 * of a function.
> >> +	 */
> >> +	for (kb = kprobe_blacklist; kb->name != NULL; kb++) {
> >> +		kprobe_lookup_name(kb->name, addr);
> >> +		if (!addr)
> >> +			continue;
> >> +
> >> +		kb->start_addr = (unsigned long)addr;
> >> +		symbol_name = kallsyms_lookup(kb->start_addr,
> >> +				&size, &offset, &modname, namebuf);
> >> +		if (!symbol_name)
> >> +			kb->range = 0;
> >> +		else
> >> +			kb->range = size;
> >> +	}
> >> +
> >> +	if (kretprobe_blacklist_size) {
> >> +		/* lookup the function address from its name */
> >> +		for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
> >> +			kprobe_lookup_name(kretprobe_blacklist[i].name,
> >> +					   kretprobe_blacklist[i].addr);
> >> +			if (!kretprobe_blacklist[i].addr)
> >> +				printk("kretprobe: lookup failed: %s\n",
> >> +				       kretprobe_blacklist[i].name);
> >> +		}
> >> +	}
> >> +	kprobe_blacklist_initialized = 1;
> > 
> > You need smp_wmb() before assigning 'kprobe_blacklist_initialized = 1'.
> > This guarantee that who see kprobe_blacklist_initialized = 1 will get
> > updated data of kprobe_blacklist.
> 
> Right, to ensure blacklist is updated, memory barrier is required.

Agreed.

> > Please refer my previous patch once more :)
> > 
> > And How about define kprobe_blacklist_initialized as boolean?
> 
> Good idea :)
> 

I'll fix it for v3.

-Oskar
> 
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