linux-kernel - Re: [PATCH] ftrace: clean up hash direct

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Message-ID: <5992B5A2-090D-49AB-8CF1-B9B2A6B15350@fb.com>
Date:   Tue, 24 May 2022 15:33:36 +0000
From:   Song Liu <songliubraving@...com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     Song Liu <song@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        Kernel Team <Kernel-team@...com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] ftrace: clean up hash direct_functions on register
 failures



> On May 24, 2022, at 7:45 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> On Thu, 12 May 2022 15:08:08 -0700
> Song Liu <song@...nel.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?

Yeah, this does look better. Do I need to send v2 with this version?

Thanks,
Song

> 
> -- 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);
>