Hi Yoshihiro,
On Mon, 17 Feb 2014 13:57:13 +0900, Yoshihiro YUNOMAE wrote:
> Hi Namhyung,
>
> (2014/02/14 13:50), Namhyung Kim wrote:
>> Hi Yoshihiro,
>>
>> On Thu, 13 Feb 2014 10:28:58 +0900, Yoshihiro YUNOMAE wrote:
>>> Introduce nr_saved_cmdlines I/F for changing the number of pid-comm list.
>>> saved_cmdlines can store 128 command names using SAVED_CMDLINES now, but
>>> 'no-existing processes' names are often lost in saved_cmdlines when we
>>> read trace data. So, by introducing nr_saved_cmdlines I/F, the rule storing
>>> 128 command names is changed to the command numbers defined users.
>>>
>>> When we write a value to nr_saved_cmdlines, the number of the value will
>>> be stored in pid-comm list:
>>>
>>> # echo 1024 > /sys/kernel/debug/tracing/nr_saved_cmdlines
>>>
>>> Here, 1024 command names are stored. The default number is 128 and the
>>> maximum
>>> number is PID_MAX_DEFAULT (=32768 if CONFIG_BASE_SMALL is not set). So, if
>>> we
>>> want to avoid to lose command names, we need to set 32768 to
>>> nr_saved_cmdlines.
>>>
>>> We can read the maximum number of the list:
>>>
>>> # cat /sys/kernel/debug/tracing/nr_saved_cmdlines
>>> 128
>>
>> [SNIP]
>>> @@ -3685,7 +3760,8 @@ static void *saved_cmdlines_next(struct seq_file *m,
>>> void *v, loff_t *pos)
>>>
>>> (*pos)++;
>>>
>>> - for (; ptr < &map_cmdline_to_pid[SAVED_CMDLINES]; ptr++) {
>>> + for (; ptr < &savedcmd->map_cmdline_to_pid[savedcmd->cmdline_num];
>>> + ptr++) {
>>> if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
>>> continue;
>>>
>>> @@ -3700,7 +3776,7 @@ static void *saved_cmdlines_start(struct seq_file *m,
>>> loff_t *pos)
>>> void *v;
>>> loff_t l = 0;
>>>
>>> - v = &map_cmdline_to_pid[0];
>>> + v = &savedcmd->map_cmdline_to_pid[0];
>>> while (l <= *pos) {
>>> v = saved_cmdlines_next(m, v, &l);
>>> if (!v)
>>
>> Are you accessing the savecmd without trace_cmdline_lock?
>
> It does not need to get trace_cmdline_lock here.
> The elements of map_pid_to_cmdline[] and saved_cmdlines[] are protected
> by trace_cmdline_lock in trace_find_cmdline(), but on the other hand
> map_cmdline_to_pid[] are not protected. There are no problems in
> particular. This is because map_cmdline_to_pid[] always refers to a
> valid process name or "<...>".
I don't get it. What does protect the savedcmd from being changed
during reading "saved_cmdlines" file with changing "nr_saved_cmdlines"?
Thanks,
Namhyung
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