[PATCH 3/7] t_next should increase position index

[PATCH 3/7] t_next should increase position index

[Vasily Averin]

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@virtuozzo.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;
+	}
 
 	if (iter->flags & FTRACE_ITER_PROBE)
 		return t_probe_next(m, pos);
-- 
1.8.3.1

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

[Steven Rostedt]

On Fri, 24 Jan 2020 10:02:51 +0300
Vasily Averin <vvs@virtuozzo.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@virtuozzo.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.

-- Steve

>  
>  	if (iter->flags & FTRACE_ITER_PROBE)
>  		return t_probe_next(m, pos);

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

[Vasily Averin]

On 1/29/20 8:12 PM, Steven Rostedt wrote:
> On Fri, 24 Jan 2020 10:02:51 +0300
> Vasily Averin <vvs@virtuozzo.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@virtuozzo.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