Messages in this thread | | | Date | Mon, 17 Feb 2014 13:57:13 +0900 | From | Yoshihiro YUNOMAE <> | Subject | Re: Re: [PATCH -tip RESEND 2/2] ftrace: Introduce nr_saved_cmdlines I/F |
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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 "<...>".
Note that we can always get process names by setting nr_saved_cmdlines to maximum number if we want to avoid to get "<...>".
Thank you, Yoshihiro YUNOMAE
-- Yoshihiro YUNOMAE Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: yoshihiro.yunomae.ez@hitachi.com
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