Simplified THD::current_linfo locking

LOG_INFO::lock was useless. It could've only protect against concurrent
iterators execution, which was already protected by LOCK_thread_count.

Use LOCK_thd_data instead of LOCK_thread_count as a protection against
THD::current_linfo reset.

Aim is to reduce usage of LOCK_thread_count and COND_thread_count.
Part of MDEV-15135.

mysql-test/suite/perfschema/r/setup_instruments_defaults.result

@@ -25,7 +25,6 @@ WHERE name IN (
 AND enabled = 'yes' AND timed = 'yes'
 ORDER BY name;
 NAME	ENABLED	TIMED
-wait/synch/mutex/sql/LOG_INFO::lock	YES	YES
 wait/synch/mutex/sql/THD::LOCK_thd_data	YES	YES
 SELECT * FROM performance_schema.setup_instruments
 WHERE name = 'wait/synch/mutex/sql/hash_filo::lock'

sql/log.h

@@ -247,10 +247,6 @@ extern TC_LOG_DUMMY tc_log_dummy;
 
 class Relay_log_info;
 
-#ifdef HAVE_PSI_INTERFACE
-extern PSI_mutex_key key_LOG_INFO_lock;
-#endif
-
 /*
   Note that we destroy the lock mutex in the desctructor here.
   This means that object instances cannot be destroyed/go out of scope,
@@ -262,19 +258,11 @@ typedef struct st_log_info
   my_off_t index_file_offset, index_file_start_offset;
   my_off_t pos;
   bool fatal; // if the purge happens to give us a negative offset
-  mysql_mutex_t lock;
   st_log_info() : index_file_offset(0), index_file_start_offset(0),
       pos(0), fatal(0)
   {
     DBUG_ENTER("LOG_INFO");
     log_file_name[0] = '\0';
-    mysql_mutex_init(key_LOG_INFO_lock, &lock, MY_MUTEX_INIT_FAST);
-    DBUG_VOID_RETURN;
-  }
-  ~st_log_info()
-  {
-    DBUG_ENTER("~LOG_INFO");
-    mysql_mutex_destroy(&lock);
     DBUG_VOID_RETURN;
   }
 } LOG_INFO;

sql/mysqld.cc

@@ -908,7 +908,7 @@ PSI_mutex_key key_BINLOG_LOCK_index, key_BINLOG_LOCK_xid_list,
   key_rpl_group_info_sleep_lock,
   key_relay_log_info_log_space_lock, key_relay_log_info_run_lock,
   key_structure_guard_mutex, key_TABLE_SHARE_LOCK_ha_data,
-  key_LOCK_error_messages, key_LOG_INFO_lock,
+  key_LOCK_error_messages,
   key_LOCK_start_thread,
   key_LOCK_thread_count, key_LOCK_thread_cache,
   key_PARTITION_LOCK_auto_inc;
@@ -1003,7 +1003,6 @@ static PSI_mutex_info all_server_mutexes[]=
   { &key_LOCK_after_binlog_sync, "LOCK_after_binlog_sync", PSI_FLAG_GLOBAL},
   { &key_LOCK_commit_ordered, "LOCK_commit_ordered", PSI_FLAG_GLOBAL},
   { &key_LOCK_slave_background, "LOCK_slave_background", PSI_FLAG_GLOBAL},
-  { &key_LOG_INFO_lock, "LOG_INFO::lock", 0},
   { &key_LOCK_thread_count, "LOCK_thread_count", PSI_FLAG_GLOBAL},
   { &key_LOCK_thread_cache, "LOCK_thread_cache", PSI_FLAG_GLOBAL},
   { &key_PARTITION_LOCK_auto_inc, "HA_DATA_PARTITION::LOCK_auto_inc", 0},

sql/sql_class.h

@@ -4934,15 +4934,15 @@ class THD :public Statement,
   }
   /*
     Reset current_linfo
-    Setting current_linfo to 0 needs to be done with LOCK_thread_count to
+    Setting current_linfo to 0 needs to be done with LOCK_thd_data to
     ensure that adjust_linfo_offsets doesn't use a structure that may
     be deleted.
   */
   inline void reset_current_linfo()
   {
-    mysql_mutex_lock(&LOCK_thread_count);
+    mysql_mutex_lock(&LOCK_thd_data);
     current_linfo= 0;
-    mysql_mutex_unlock(&LOCK_thread_count);
+    mysql_mutex_unlock(&LOCK_thd_data);
   }
 
 

sql/sql_repl.cc

@@ -537,9 +537,9 @@ void adjust_linfo_offsets(my_off_t purge_offset)
   while ((tmp=it++))
   {
     LOG_INFO* linfo;
+    mysql_mutex_lock(&tmp->LOCK_thd_data);
     if ((linfo = tmp->current_linfo))
     {
-      mysql_mutex_lock(&linfo->lock);
       /*
 	Index file offset can be less that purge offset only if
 	we just started reading the index file. In that case
@@ -549,8 +549,8 @@ void adjust_linfo_offsets(my_off_t purge_offset)
 	linfo->fatal = (linfo->index_file_offset != 0);
       else
 	linfo->index_file_offset -= purge_offset;
-      mysql_mutex_unlock(&linfo->lock);
     }
+    mysql_mutex_unlock(&tmp->LOCK_thd_data);
   }
   mysql_mutex_unlock(&LOCK_thread_count);
 }
@@ -568,14 +568,12 @@ bool log_in_use(const char* log_name)
   while ((tmp=it++))
   {
     LOG_INFO* linfo;
+    mysql_mutex_lock(&tmp->LOCK_thd_data);
     if ((linfo = tmp->current_linfo))
-    {
-      mysql_mutex_lock(&linfo->lock);
       result = !memcmp(log_name, linfo->log_file_name, log_name_len);
-      mysql_mutex_unlock(&linfo->lock);
-      if (result)
-	break;
-    }
+    mysql_mutex_unlock(&tmp->LOCK_thd_data);
+    if (result)
+      break;
   }
 
   mysql_mutex_unlock(&LOCK_thread_count);