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SubjectRe: 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@hitachi.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@hitachi.com




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