[MDEV-5181] incorrect binary search in remove_status_vars() Created: 2013-10-24  Updated: 2013-11-08  Resolved: 2013-11-08

Status: Closed
Project: MariaDB Server
Component/s: None
Affects Version/s: 10.0.4, 5.5.33a
Fix Version/s: 5.5.34, 10.0.6

Type: Bug Priority: Critical
Reporter: Sergei Golubchik Assignee: Alexander Barkov
Resolution: Fixed Votes: 1
Labels: plugins


 Description   

On INSTALL SONAME 'ha_tokudb.so' when TokuDB cannot be installed (for example, because transparent hugepages are enabled), MariaDB hangs.

The reason is the remove_status_vars() function that has incorrectly implemented binary search to remove plugin variables from the all-variables list. The code

      for (; b-a > 0; c= (a+b)/2)
 
      {
 
        res= show_var_cmp(list, all+c);
 
        if (res < 0)
 
          b= c;
 
        else if (res > 0)
 
          a= c;
 
        else
 
          break;
 
      }

in my test, a=129, b=130. So, c=129, in comparison I get res > 0, and the loop continues till infinity.

 Comments   
Comment by Patryk Pomykalski [ 2013-11-06 ]

I came up with something like this:

— sql/sql_show.cc 2013-07-16 17:09:54 +0000
+++ sql/sql_show.cc 2013-11-05 21:59:41 +0000
@@ -2550,17 +2550,18 @@

for (; list->name; list++)
{

  • int res= 0, a= 0, b= all_status_vars.elements, c= (a+b)/2;
  • for (; b-a > 0; c= (a+b)/2)
    + int res= 0, a= 0, b= all_status_vars.elements, c;
    + do { + c= (a+b)/2; res= show_var_cmp(list, all+c); if (res < 0) - b= c; + b= c - 1; else if (res > 0) - a= c; + a= c + 1; else break; - }

    + } while (b >= a && a < all_status_vars.elements);
    if (res == 0)
    all[c].type= SHOW_UNDEF;
    }

Comment by Alexander Barkov [ 2013-11-08 ]

Pushed into 5.1, 5.2, 5.3, 5.5, 10.0-base.

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