Driver QMysql can't be loaded

[Olivier Subilia]

The faulty package is libmysqlclient21, installed automatically
(http://ch.archive.ubuntu.com/ubuntu focal/main amd64)
but launchpad complains about "libmysqlclient" does not exist in Ubuntu...

I Use a programm writen in python / PyQt5 to access a mysql database, which has always functioned.
Since upgrade to libmysqlclient21 8.0.21-0ubuntu0.20.04.3, I have a continual "Database Error:Driver not loaded Driver not loaded" "QMYSQL driver not loaded"
Reinstalling libmysqlclient21 8.0.19-0ubuntu5 (which worked before) solved the problem.
I suppose it's a regression bug

Ubuntu version: Ubuntu 20.04.1 LTS

[Ubuntu Foundations Team Bug Bot (crichton)]

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[Olivier Subilia (osubillia)]

Sorry. I've just understood the difference between source package and installed package name (I should use apt show more often...)

Completely minimal example:

#!/usr/bin/python3
# -*- coding: utf-8 -*-

import sys
from PyQt5.QtWidgets import QApplication
from PyQt5.QtSql import QSqlDatabase

app = QApplication(sys.argv)
db = QSqlDatabase.addDatabase("QMYSQL")

with libmysqlclient21=8.0.19-0ubuntu5:
(OK)
with libmysqlclient21=8.0.21-0ubuntu0.20.04.3:
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QMYSQL QMYSQL3

[Christian Ehrhardt  (paelzer)]

Hi Olivier,
thanks for the report - I can confirm that this triggers the issue:

$ apt install python3-pyqt5 python3-pyqt5.qtsql libqt5sql5-mysql
$ cat > test.py << EOF
#!/usr/bin/python3

# -*- coding: utf-8 -*-

import sys
from PyQt5.QtWidgets import QApplication
from PyQt5.QtSql import QSqlDatabase

app = QApplication(sys.argv)
db = QSqlDatabase.addDatabase("QMYSQL")
EOF
$ python3 test.py

And also that I can switch in/out of the behavior between versions 8.0.21-0ubuntu0.20.04.3 / 8.0.19-0ubuntu5 of libmysqlclient21.

[Lars Tangvald (lars-tangvald)]

Thanks for the report and test case! I'll test it, and pass it on upstream.

[Marc Deslauriers (mdeslaur)]

I think this may be related:

$ readelf --dynamic libmysqlclient.so.21.1.19 | grep BIND
 0x000000000000001e (FLAGS) BIND_NOW

$ readelf --dynamic libmysqlclient.so.21.1.21 | grep BIND
 0x000000000000001e (FLAGS) BIND_NOW STATIC_TLS

[Marc Deslauriers (mdeslaur)]

Possibly related:
https://github.com/mysql/mysql-server/commit/735bd2a53834266c7256830c8d34672ea55fe17b

[Lars Tangvald (lars-tangvald)]

Verified with upstream packages as well. The test case also works as expected with 8.0.20, so it was introduced in 8.0.21.

I'll do a test build to see if reverting that commit fixes it. Thanks for the tip, Marc :)

[Christian Ehrhardt  (paelzer)]

As loaded by python:
0x00007ffff2dd4460 0x00007ffff2e0304e Yes (*) /lib/x86_64-linux-gnu/libQt5Sql.so.5

I was trying to get a different POV on the same lib, removing python out of the picture.

Install mysql and create a DB.

$ apt install mysql-server
$ systemctl start mysql
$ systemctl status mysql
$ mysql -u root
mysql> CREATE USER 'newuser'@'localhost' IDENTIFIED BY 'user_password';
mysql> CREATE DATABASE test;
mysql> GRANT ALL PRIVILEGES ON test.* TO 'newuser'@'localhost';
mysql> USE test;
mysql> CREATE TABLE testtable (id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY);

Test Program:

# cat mysqlqt.pro
######################################################################
# Automatically generated by qmake (3.1) Tue Aug 4 12:46:45 2020
######################################################################

TEMPLATE = app
TARGET = mysqlqt
INCLUDEPATH += .
INCLUDEPATH += /usr/include/x86_64-linux-gnu/qt5
INCLUDEPATH += /usr/include/x86_64-linux-gnu/qt5/QtCore
INCLUDEPATH += /usr/include/x86_64-linux-gnu/qt5/QtGui
INCLUDEPATH += /usr/include/x86_64-linux-gnu/qt5/QtWidgets

QT += core gui sql
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

# The following define makes your compiler warn you if you use any
# feature of Qt which has been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0

# Input
SOURCES += mysqlqt.cpp

# cat mysqlqt.cpp
#include <QApplication>
#include <QPushButton>
#include <QSqlDatabase>

int main()
{
    QStringList drivers = QSqlDatabase::drivers();
    for(int i=0 ; i < drivers.length() ; i++) {
        qDebug("driver: %s", qUtf8Printable(drivers[i]));
    }

    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    db.setHostName("localhost");
    db.setDatabaseName("test");
    db.setUserName("newuser");
    db.setPassword("user_password");
    bool ok = db.open();

    qDebug("ok %i isopen %i isvalid %i", ok, db.isOpen(), db.isValid());
    qDebug("db-driver %s", qUtf8Printable(db.driverName()));

    qDebug("# start tables");
    QStringList tables = db.tables();
    for(int i=0 ; i < tables.length() ; i++) {
        qDebug("table: %s", qUtf8Printable(tables[i]));
    }
    qDebug("# end tables");

    return ok;
}

$ ./mysqlqt
driver: QSQLITE
driver: QMYSQL
driver: QMYSQL3
ok 1 isopen 1 isvalid 1
db-driver QMYSQL
# start tables
table: testtable
# end tables

So the QMYSQL isn't generally disfunctional since this update, it must be related to something more specific in the python wrapping of it.

[Lars Tangvald (lars-tangvald)]

Verified that reverting the commit Marc suggested makes the test case pass.

If I understand it correctly, STATIC_TLS is a limited resource, so if the python wrapping loads other libraries that also use it, but your c program doesn't?

[Marc Deslauriers (mdeslaur)]

Lars, I think that is what is happening, yes.

[Marc Deslauriers (mdeslaur)]

(See bug 1890170 for another reproducer)

[Lars Tangvald (lars-tangvald)]

A simpler fix is to add a cmake flag to override the tls-model flag:

-DCMAKE_CXX_FLAGS="-ftls-model=global-dynamic" \

to debian/rules

[Launchpad Janitor (janitor)]

This bug was fixed in the package mysql-8.0 - 8.0.21-0ubuntu0.20.04.4

---------------
mysql-8.0 (8.0.21-0ubuntu0.20.04.4) focal-security; urgency=medium

  * SECURITY REGRESSION: libmysqlclient loading issues (LP: #1889851)
    - debian/patches/revert_faster_tls_model.patch: revert an upstream
      commit that switches the tls-model to initial-exec. This is causing
      "cannot allocate memory in static TLS block" errors when attempting
      to load the library in certain scenarios.

 -- Marc Deslauriers <email address hidden> Tue, 04 Aug 2020 07:39:21 -0400

[Launchpad Janitor (janitor)]

This bug was fixed in the package mysql-8.0 - 8.0.21-0ubuntu4

---------------
mysql-8.0 (8.0.21-0ubuntu4) groovy; urgency=medium

  * SECURITY REGRESSION: libmysqlclient loading issues (LP: #1889851)
    - debian/patches/revert_faster_tls_model.patch: revert an upstream
      commit that switches the tls-model to initial-exec. This is causing
      "cannot allocate memory in static TLS block" errors when attempting
      to load the library in certain scenarios.

 -- Marc Deslauriers <email address hidden> Tue, 04 Aug 2020 07:39:21 -0400

[Jose (jortuno)]

I would like to report the same problem happening again with the latest version of libmysqlclient21.
I am speaking about this bug:
https://stackoverflow.com/questions/63307453/cannot-allocate-memory-in-static-tls-block-in-a-python-flask-application

Which again was solved downgrading to the previous version: 8.0.28-0ubuntu0.20.04.3

Thanks :)

[Marc Deslauriers (mdeslaur)]

8.0.28-0ubuntu0.20.04.3 is the current version, and it still contains the patch for this issue.

What version did you install that triggered the issue, and where did you get it?