linux-kernel - Re: Re: [PATCH ftrace/core 2/2] ftrace, kprobes: Support IPMODIFY flag to find IP modify conflict

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Message-ID: <53994F67.9030106@hitachi.com>
Date:	Thu, 12 Jun 2014 15:57:43 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: Re: [PATCH ftrace/core  2/2] ftrace, kprobes: Support IPMODIFY
 flag to find IP modify conflict

(2014/06/12 14:54), Namhyung Kim wrote:
> On Thu, 12 Jun 2014 12:29:09 +0900, Masami Hiramatsu wrote:
>> NO, ftrace_lookup_ip() returns NULL if the hash is empty, so adding
>> !ftrace_hash_empty() is meaningless :)
>>
>> Actually, here I intended to have 3 meanings for the new/old_hash arguments,
>> - If it is NULL, it hits all
>> - If it is EMPTY_HASH, it hits nothing
>> - If it has some entries, it hits those entries.
>>
>> And in ftrace.c(__ftrace_hash_rec_update), AFAICS, ops->filter_hash has only
>> 2 meanings,
>> - If it is EMPTY_HASH or NULL, it hits all
>> - If it has some entries, it hits those entries.
> 
> Then I found an unrelated issue during review.
> 
> It seems that checking NULL other_hash for the 'all' case in
> __ftrace_hash_rec_update() is not sufficient.  It should check
> EMPTY_HASH case too, but then it ends up removing the check at all since
> it can be covered in ftrace_lookup_ip().

I guessed that was just for speeding up by skipping ftrace_lookup_ip().
(but I'm not sure how much it improves...)

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

However, I'd like to ask Steven his Ack.

Thank you,

> 
> Thanks,
> Namhyung
> 
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 13885590a184..8bd7aa69a479 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1545,7 +1545,7 @@ static void __ftrace_hash_rec_update(struct ftrace_ops *ops,
>  			 * Only the filter_hash affects all records.
>  			 * Update if the record is not in the notrace hash.
>  			 */
> -			if (!other_hash || !ftrace_lookup_ip(other_hash, rec->ip))
> +			if (!ftrace_lookup_ip(other_hash, rec->ip))
>  				match = 1;
>  		} else {
>  			in_hash = !!ftrace_lookup_ip(hash, rec->ip);
> --
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> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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