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

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Date:	Thu, 12 Jun 2014 14:54:53 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.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>
Subject: Re: [PATCH ftrace/core  2/2] ftrace, kprobes: Support IPMODIFY flag to find IP modify conflict

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().

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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