linux-kernel - Re: [PATCH 3/7] t_next should increase position index

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Message-ID: <61c69254-2743-16ab-ea7d-ce110fb20cd5@virtuozzo.com>
Date:   Thu, 30 Jan 2020 10:17:53 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        NeilBrown <neilb@...e.com>, Waiman Long <longman@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>
Subject: Re: [PATCH 3/7] t_next should increase position index

On 1/29/20 8:12 PM, Steven Rostedt wrote:
> On Fri, 24 Jan 2020 10:02:51 +0300
> Vasily Averin <vvs@...tuozzo.com> wrote:
> 
>> if seq_file .next fuction does not change position index,
>> read after some lseek can generate unexpected output.
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=206283
>> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
>> ---
>>  kernel/trace/ftrace.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>> index 9bf1f2c..ca25210 100644
>> --- a/kernel/trace/ftrace.c
>> +++ b/kernel/trace/ftrace.c
>> @@ -3442,8 +3442,10 @@ static void *t_mod_start(struct seq_file *m, loff_t *pos)
>>  	loff_t l = *pos; /* t_probe_start() must use original pos */
>>  	void *ret;
>>  
>> -	if (unlikely(ftrace_disabled))
>> +	if (unlikely(ftrace_disabled)) {
>> +		(*pos)++;
>>  		return NULL;
>> +	}
> 
> This isn't needed. If ftrace_disabled is set, we shouldn't be printing
> anything. This case isn't the same as the report in the bugzilla.

I'm agree, thank you, let's drop this patch.

Vasily Averin