Fixed bug#54486 - assert in my_seek, concurrent

DROP/CREATE SCHEMA, CREATE TABLE, REPAIR.

The cause of assert was concurrent execution of
DROP DATABASE and REPAIR TABLE where first statement
deleted table's file .TMD at the same time as
REPAIR TABLE tried to read file details from the old file
that was just removed.

Additionally was fixed trouble when DROP TABLE try delete
all files belong to table being dropped at the same time
when REPAIR TABLE statement has just deleted .TMD file.

No regression test added because this would require adding a
sync point to mysys/my_redel.c. Since this bug is not present in
5.5+, adding test coverage was considered unnecessary.
The patch has been verified using RQG testing.

sql/sql_db.cc

@@ -948,9 +948,6 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
     remove_db_from_cache(db);
     pthread_mutex_unlock(&LOCK_open);
 
-    Drop_table_error_handler err_handler(thd->get_internal_handler());
-    thd->push_internal_handler(&err_handler);
-
     error= -1;
     /*
       We temporarily disable the binary log while dropping the objects
@@ -983,8 +980,8 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
       error = 0;
       reenable_binlog(thd);
     }
-    thd->pop_internal_handler();
   }
+
   if (!silent && deleted>=0)
   {
     const char *query;
@@ -1213,16 +1210,34 @@ static long mysql_rm_known_files(THD *thd, MY_DIR *dirp, const char *db,
     else
     {
       strxmov(filePath, org_path, "/", file->name, NullS);
-      if (my_delete_with_symlink(filePath,MYF(MY_WME)))
+      /*
+        We ignore ENOENT error in order to skip files that was deleted
+        by concurrently running statement like REAPIR TABLE ...
+      */
+      if (my_delete_with_symlink(filePath, MYF(0)) &&
+          my_errno != ENOENT)
       {
-	goto err;
+        my_error(EE_DELETE, MYF(0), filePath, my_errno);
+        goto err;
       }
     }
   }
-  if (thd->killed ||
-      (tot_list && mysql_rm_table_part2(thd, tot_list, 1, 0, 1, 1)))
+
+  if (thd->killed)
     goto err;
 
+  if (tot_list)
+  {
+    int res= 0;
+    Drop_table_error_handler err_handler(thd->get_internal_handler());
+
+    thd->push_internal_handler(&err_handler);
+    res= mysql_rm_table_part2(thd, tot_list, 1, 0, 1, 1);
+    thd->pop_internal_handler();
+    if (res)
+      goto err;
+  }
+
   /* Remove RAID directories */
   {
     List_iterator<String> it(raid_dirs);

storage/myisam/mi_check.c

@@ -1741,6 +1741,8 @@ err:
 			     MYF(MY_REDEL_MAKE_BACKUP): MYF(0))) ||
 	  mi_open_datafile(info,share,name,-1))
 	got_error=1;
+
+      param->retry_repair= 0;
     }
   }
   if (got_error)