Protect shared variables with log lock. (netdata#13306)

Fixes reports by helgrind:

```
==00:00:00:01.769 44512== Possible data race during read of size 8 at 0x9767B0 by thread #4
==00:00:00:01.769 44512== Locks held: none
==00:00:00:01.769 44512==    at 0x17CB56: error_log_limit (log.c:627)
==00:00:00:01.769 44512==    by 0x17CEC0: info_int (log.c:716)
==00:00:00:01.769 44512==    by 0x18949F: thread_start (threads.c:173)
==00:00:00:01.769 44512==    by 0x484A486: ??? (in /usr/libexec/valgrind/vgpreload_helgrind-amd64-linux.so)
==00:00:00:01.769 44512==    by 0x4E9CD7F: start_thread (pthread_create.c:481)
==00:00:00:01.769 44512==    by 0x532F76E: clone (clone.S:95)
==00:00:00:01.769 44512==
==00:00:00:01.769 44512== This conflicts with a previous write of size 8 by thread #3
==00:00:00:01.769 44512== Locks held: none
==00:00:00:01.769 44512==    at 0x17CB61: error_log_limit (log.c:627)
==00:00:00:01.769 44512==    by 0x17CEC0: info_int (log.c:716)
==00:00:00:01.769 44512==    by 0x18949F: thread_start (threads.c:173)
==00:00:00:01.769 44512==    by 0x484A486: ??? (in /usr/libexec/valgrind/vgpreload_helgrind-amd64-linux.so)
==00:00:00:01.769 44512==    by 0x4E9CD7F: start_thread (pthread_create.c:481)
==00:00:00:01.769 44512==    by 0x532F76E: clone (clone.S:95)
==00:00:00:01.769 44512==  Address 0x9767b0 is 0 bytes inside data symbol "counter.1"
```

```
==00:00:00:44.536 47685==  Lock at 0x976720 was first observed
==00:00:00:44.536 47685==    at 0x48477EF: ??? (in /usr/libexec/valgrind/vgpreload_helgrind-amd64-linux.so)
==00:00:00:44.536 47685==    by 0x17BBF4: __netdata_mutex_lock (locks.c:86)
==00:00:00:44.536 47685==    by 0x17C514: log_lock (log.c:471)
==00:00:00:44.536 47685==    by 0x17CEC0: info_int (log.c:715)
==00:00:00:44.536 47685==    by 0x458C9E: compute_multidb_diskspace (rrdenginelib.c:279)
==00:00:00:44.536 47685==    by 0x15B170: get_netdata_configured_variables (main.c:671)
==00:00:00:44.536 47685==    by 0x15CE6C: main (main.c:1263)
==00:00:00:44.536 47685==  Address 0x976720 is 0 bytes inside data symbol "log_mutex"
==00:00:00:44.536 47685==
==00:00:00:44.536 47685== Possible data race during write of size 8 at 0x9767A0 by thread #1
==00:00:00:44.536 47685== Locks held: none
==00:00:00:44.536 47685==    at 0x17CB39: error_log_limit (log.c:621)
==00:00:00:44.536 47685==    by 0x15E234: signals_handle (signals.c:258)
==00:00:00:44.536 47685==    by 0x15D880: main (main.c:1534)
==00:00:00:44.536 47685==
==00:00:00:44.536 47685== This conflicts with a previous read of size 8 by thread #9
==00:00:00:44.536 47685== Locks held: 1, at address 0x976720
==00:00:00:44.536 47685==    at 0x17CAA3: error_log_limit (log.c:604)
==00:00:00:44.536 47685==    by 0x17CECA: info_int (log.c:718)
==00:00:00:44.536 47685==    by 0x4624D2: rrdset_done_push (rrdpush.c:344)
==00:00:00:44.536 47685==    by 0x36190C: rrdset_done (rrdset.c:1351)
==00:00:00:44.536 47685==    by 0x1B07E7: Chart::update(unsigned long) (plugin_profile.cc:82)
==00:00:00:44.536 47685==    by 0x1B01D4: updateCharts(std::vector<Chart*, std::allocator<Chart*> >, unsigned long) (plugin_profile.cc:126)
==00:00:00:44.536 47685==    by 0x1B02AC: profile_main (plugin_profile.cc:144)
==00:00:00:44.536 47685==    by 0x1895D4: thread_start (threads.c:185)
==00:00:00:44.536 47685==  Address 0x9767a0 is 0 bytes inside data symbol "start.3"
```

libnetdata/log/log.c

@@ -681,6 +681,26 @@ int error_log_limit(int reset) {
     return 0;
 }
 
+void error_log_limit_reset(void) {
+    log_lock();
+
+    error_log_errors_per_period = error_log_errors_per_period_backup;
+    error_log_limit(1);
+
+    log_unlock();
+}
+
+void error_log_limit_unlimited(void) {
+    log_lock();
+
+    error_log_errors_per_period = error_log_errors_per_period_backup;
+    error_log_limit(1);
+
+    error_log_errors_per_period = ((error_log_errors_per_period_backup * 10) < 10000) ? 10000 : (error_log_errors_per_period_backup * 10);
+
+    log_unlock();
+}
+
 // ----------------------------------------------------------------------------
 // debug log
 
@@ -712,8 +732,13 @@ void info_int( const char *file, const char *function, const unsigned long line,
 {
     va_list args;
 
+    log_lock();
+
     // prevent logging too much
-    if(error_log_limit(0)) return;
+    if (error_log_limit(0)) {
+        log_unlock();
+        return;
+    }
 
     if(error_log_syslog) {
         va_start( args, fmt );
@@ -724,8 +749,6 @@ void info_int( const char *file, const char *function, const unsigned long line,
     char date[LOG_DATE_LENGTH];
     log_date(date, LOG_DATE_LENGTH);
 
-    log_lock();
-
     va_start( args, fmt );
 #ifdef NETDATA_INTERNAL_CHECKS
     fprintf(stderr, "%s: %s INFO  : %s : (%04lu@%-20.20s:%-15.15s): ", date, program_name, netdata_thread_tag(), line, file, function);
@@ -771,8 +794,13 @@ void error_int( const char *prefix, const char *file, const char *function, cons
 
     va_list args;
 
+    log_lock();
+
     // prevent logging too much
-    if(error_log_limit(0)) return;
+    if (error_log_limit(0)) {
+        log_unlock();
+        return;
+    }
 
     if(error_log_syslog) {
         va_start( args, fmt );
@@ -783,8 +811,6 @@ void error_int( const char *prefix, const char *file, const char *function, cons
     char date[LOG_DATE_LENGTH];
     log_date(date, LOG_DATE_LENGTH);
 
-    log_lock();
-
     va_start( args, fmt );
 #ifdef NETDATA_INTERNAL_CHECKS
     fprintf(stderr, "%s: %s %-5.5s : %s : (%04lu@%-20.20s:%-15.15s): ", date, program_name, prefix, netdata_thread_tag(), line, file, function);

libnetdata/log/log.h

@@ -74,11 +74,8 @@ extern void reopen_all_log_files();
 
 static inline void debug_dummy(void) {}
 
-#define error_log_limit_reset() do { error_log_errors_per_period = error_log_errors_per_period_backup; error_log_limit(1); } while(0)
-#define error_log_limit_unlimited() do { \
-        error_log_limit_reset(); \
-        error_log_errors_per_period = ((error_log_errors_per_period_backup * 10) < 10000) ? 10000 : (error_log_errors_per_period_backup * 10); \
-    } while(0)
+void error_log_limit_reset(void);
+void error_log_limit_unlimited(void);
 
 #ifdef NETDATA_INTERNAL_CHECKS
 #define debug(type, args...) do { if(unlikely(debug_flags & type)) debug_int(__FILE__, __FUNCTION__, __LINE__, ##args); } while(0)