modprobe-small: if concurrent module load did not succeed, wait

usecase:
two sd cards are being mounted in parallel at same time on dual core. example
modules which are getting loaded is  nls_cp437. While one module is being
loaded , it makes state in /proc/modules as 'coming' and then starts doing its
module init function (in our case - registering nls). meanwhile on other core,
if modprobe returns that is has already been loaded, then it will continue
and search for the nls list which is not yet finished from first module init.
This fails resulting in not mounting sd card.

function                                             old     new   delta
process_module                                       667     746     +79

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/modutils/modprobe-small.c b/modutils/modprobe-small.c
index 6b0a4400c999da14b6e2931edd034cfa542345c2..598965968f826be214eaf8da588bee2b20c6ad06 100644 (file)
--- a/modutils/modprobe-small.c
+++ b/modutils/modprobe-small.c
@@ -536,17 +536,49 @@ static module_info** find_alias(const char *alias)
 // TODO: open only once, invent config_rewind()
 static int already_loaded(const char *name)
 {
-       int ret = 0;
-       char *s;
-       parser_t *parser = config_open2("/proc/modules", xfopen_for_read);
-       while (config_read(parser, &s, 1, 1, "# \t", PARSE_NORMAL & ~PARSE_GREEDY)) {
-               if (strcmp(s, name) == 0) {
-                       ret = 1;
-                       break;
+       int ret, namelen;
+       char *line;
+       FILE *fp;
+
+       ret = 5 * 2;
+ again:
+       fp = fopen_for_read("/proc/modules");
+       if (!fp)
+               return 0;
+       namelen = strlen(name);
+       while ((line = xmalloc_fgetline(fp)) != NULL) {
+               char *live;
+
+               // Examples from kernel 3.14.6:
+               //pcspkr 12718 0 - Live 0xffffffffa017e000
+               //snd_timer 28690 2 snd_seq,snd_pcm, Live 0xffffffffa025e000
+               //i915 801405 2 - Live 0xffffffffa0096000
+               if (strncmp(line, name, namelen) != 0 || line[namelen] != ' ') {
+                       free(line);
+                       continue;
                }
+               live = strstr(line, " Live");
+               free(line);
+               if (!live) {
+                       /* State can be Unloading, Loading, or Live.
+                        * modprobe must not return prematurely if we see "Loading":
+                        * it can cause further programs to assume load completed,
+                        * but it did not (yet)!
+                        * Wait up to 5*20 ms for it to resolve.
+                        */
+                       ret -= 2;
+                       if (ret == 0)
+                               break;  /* huh? report as "not loaded" */
+                       fclose(fp);
+                       usleep(20*1000);
+                       goto again;
+               }
+               ret = 1;
+               break;
        }
-       config_close(parser);
-       return ret;
+       fclose(fp);
+
+       return ret | 1;
 }
 #else
 #define already_loaded(name) 0