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Date:   Tue, 24 May 2022 10:45:27 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Song Liu <song@kernel.org>
Cc:     <linux-kernel@vger.kernel.org>, <mingo@redhat.com>,
        <kernel-team@fb.com>, <stable@vger.kernel.org>
Subject: Re: [PATCH] ftrace: clean up hash direct_functions on register
 failures
Message-ID: <20220524104527.3a07878d@gandalf.local.home>
In-Reply-To: <20220512220808.766832-1-song@kernel.org>
References: <20220512220808.766832-1-song@kernel.org>
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On Thu, 12 May 2022 15:08:08 -0700
Song Liu <song@kernel.org> wrote:

> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -4465,7 +4465,7 @@ int ftrace_func_mapper_add_ip(struct ftrace_func_mapper *mapper,
>   * @ip: The instruction pointer address to remove the data from
>   *
>   * Returns the data if it is found, otherwise NULL.
> - * Note, if the data pointer is used as the data itself, (see 
> + * Note, if the data pointer is used as the data itself, (see
>   * ftrace_func_mapper_find_ip(), then the return value may be meaningless,
>   * if the data pointer was set to zero.
>   */
> @@ -5200,8 +5200,10 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
>  
>  	if (!ret && !(direct_ops.flags & FTRACE_OPS_FL_ENABLED)) {
>  		ret = register_ftrace_function(&direct_ops);
> -		if (ret)
> +		if (ret) {
>  			ftrace_set_filter_ip(&direct_ops, ip, 1, 0);
> +			remove_hash_entry(direct_functions, entry);
> +		}
>  	}
>  
>  	if (ret) {

Perhaps something like this is more robust?

-- Steve

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4f1d2f5e7263..cd38ad490174 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5195,8 +5195,6 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
 		goto out_unlock;
 
 	ret = ftrace_set_filter_ip(&direct_ops, ip, 0, 0);
-	if (ret)
-		remove_hash_entry(direct_functions, entry);
 
 	if (!ret && !(direct_ops.flags & FTRACE_OPS_FL_ENABLED)) {
 		ret = register_ftrace_function(&direct_ops);
@@ -5205,6 +5203,7 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
 	}
 
 	if (ret) {
+		remove_hash_entry(direct_functions, entry);
 		kfree(entry);
 		if (!direct->count) {
 			list_del_rcu(&direct->next);