MDEV-7188 main.signal_demo3 and sys_vars.max_sp_recursion_depth_func fail in...

MDEV-7188 main.signal_demo3 and sys_vars.max_sp_recursion_depth_func fail in biuldbot on labrador with Thread stack overrun

reduce stack requirememnts for CALL by just a little bit

sql/sp_head.cc

@@ -1131,31 +1131,8 @@ sp_head::execute(THD *thd, bool merge_da_on_success)
   Diagnostics_area *da= thd->get_stmt_da();
   Warning_info sp_wi(da->warning_info_id(), false, true);
 
-  /*
-    Just reporting a stack overrun error
-    (@sa check_stack_overrun()) requires stack memory for error
-    message buffer. Thus, we have to put the below check
-    relatively close to the beginning of the execution stack,
-    where available stack margin is still big. As long as the check
-    has to be fairly high up the call stack, the amount of memory
-    we "book" for has to stay fairly high as well, and hence
-    not very accurate. The number below has been calculated
-    by trial and error, and reflects the amount of memory necessary
-    to execute a single stored procedure instruction, be it either
-    an SQL statement, or, heaviest of all, a CALL, which involves
-    parsing and loading of another stored procedure into the cache
-    (@sa db_load_routine() and Bug#10100).
-    At the time of measuring, a recursive SP invocation required
-    3232 bytes of stack on 32 bit Linux, 6016 bytes on 64 bit Mac
-    and 11152 on 64 bit Solaris sparc.
-    The same with db_load_routine() required circa 7k bytes and
-    14k bytes accordingly. Hence, here we book the stack with some
-    reasonable margin.
-
-    Reverting back to 8 * STACK_MIN_SIZE until further fix.
-    8 * STACK_MIN_SIZE is required on some exotic platforms.
-  */
-  if (check_stack_overrun(thd, 8 * STACK_MIN_SIZE, (uchar*)&old_packet))
+  /* this 7*STACK_MIN_SIZE is a complex matter with a long history (see it!) */
+  if (check_stack_overrun(thd, 7 * STACK_MIN_SIZE, (uchar*)&old_packet))
     DBUG_RETURN(TRUE);
 
   /* init per-instruction memroot */