[bug report] tracing: Allow whitespace to surround hist trigger filter

[Dan Carpenter <dan.carpenter@oracle.com>]

[ This is an older warning but renaming the function made it appear in
  the new warnings list.  I have searched my outbox and I don't think
  I forwarded this one before.  -dan ]

Hello Tom Zanussi,

The patch ec5ce0987541: "tracing: Allow whitespace to surround hist
trigger filter" from Jan 15, 2018, leads to the following Smatch
static checker warning:

	kernel/trace/trace_events_hist.c:6199 event_hist_trigger_parse()
	warn: 'p' can't be NULL.

kernel/trace/trace_events_hist.c
    6149 static int event_hist_trigger_parse(struct event_command *cmd_ops,
    6150                                     struct trace_event_file *file,
    6151                                     char *glob, char *cmd, char *param)
    6152 {
    6153         unsigned int hist_trigger_bits = TRACING_MAP_BITS_DEFAULT;
    6154         struct event_trigger_data *trigger_data;
    6155         struct hist_trigger_attrs *attrs;
    6156         struct event_trigger_ops *trigger_ops;
    6157         struct hist_trigger_data *hist_data;
    6158         struct synth_event *se;
    6159         const char *se_name;
    6160         bool remove = false;
    6161         char *trigger, *p, *start;
    6162         int ret = 0;
    6163 
    6164         lockdep_assert_held(&event_mutex);
    6165 
    6166         if (glob && strlen(glob)) {
    6167                 hist_err_clear();
    6168                 last_cmd_set(file, param);
    6169         }
    6170 
    6171         if (!param)
    6172                 return -EINVAL;
    6173 
    6174         if (glob[0] == '!')
    6175                 remove = true;
    6176 
    6177         /*
    6178          * separate the trigger from the filter (k:v [if filter])
    6179          * allowing for whitespace in the trigger
    6180          */
    6181         p = trigger = param;
    6182         do {
    6183                 p = strstr(p, "if");
    6184                 if (!p)
    6185                         break;
    6186                 if (p == param)
    6187                         return -EINVAL;
    6188                 if (*(p - 1) != ' ' && *(p - 1) != '\t') {
    6189                         p++;
    6190                         continue;
                                 ^^^^^^^^^

These are the continue paths

    6191                 }
    6192                 if (p >= param + strlen(param) - (sizeof("if") - 1) - 1)
    6193                         return -EINVAL;
    6194                 if (*(p + sizeof("if") - 1) != ' ' && *(p + sizeof("if") - 1) != '\t') {
    6195                         p++;
    6196                         continue;
                                 ^^^^^^^^^

    6197                 }
    6198                 break;
--> 6199         } while (p);

Should this be } while(*p);?

    6200 
    6201         if (!p)
    6202                 param = NULL;
    6203         else {
    6204                 *(p - 1) = '\0';
    6205                 param = strstrip(p);
    6206                 trigger = strstrip(trigger);
    6207         }
    6208 

regards,
dan carpenter