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From 276fa8383a7535765be7182883ef4aade17ce013 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Thu, 2 Apr 2020 12:08:41 -0300
Subject: [PATCH] QLibrary: fix deadlock caused by fix to QTBUG-39642
Commit ae6f73e8566fa76470937aca737141183929a5ec inserted a mutex around
the entire load_sys(). We had reasoed that deadlocks would only occur if
the object creation in instance() recursed into its own instance(),
which was already a bug. But we had forgotten that dlopen()/
LoadLibrary() executes initialization code from the module being loaded,
which could cause a recursion back into the same QPluginLoader or
QLibrary object. This recursion is benign because the module *is* loaded
and dlopen()/LoadLibrary() returns the same handle.
[ChangeLog][QtCore][QLibrary and QPluginLoader] Fixed a deadlock that
would happen if the plugin or library being loaded has load-time
initialization code (C++ global variables) that recursed back into the
same QLibrary or QPluginLoader object.
PS: QLibraryPrivate::loadPlugin() updates pluginState outside a mutex
lock, so pluginState should be made an atomic variable. Once that is
done, we'll only need locking the mutex to update errorString (no
locking before loading).
Fixes: QTBUG-83207
Task-number: QTBUG-39642
Change-Id: Ibdc95e9af7bd456a94ecfffd160209304e5ab2eb
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>
---
src/corelib/plugin/qlibrary.cpp | 2 --
src/corelib/plugin/qlibrary_unix.cpp | 4 ++++
src/corelib/plugin/qlibrary_win.cpp | 3 +++
3 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/src/corelib/plugin/qlibrary.cpp b/src/corelib/plugin/qlibrary.cpp
index ddb053c26fa..be9d92b2048 100644
--- a/src/corelib/plugin/qlibrary.cpp
+++ b/src/corelib/plugin/qlibrary.cpp
@@ -576,9 +576,7 @@ bool QLibraryPrivate::load()
Q_TRACE(QLibraryPrivate_load_entry, fileName);
- mutex.lock();
bool ret = load_sys();
- mutex.unlock();
if (qt_debug_component()) {
if (ret) {
qDebug() << "loaded library" << fileName;
diff --git a/src/corelib/plugin/qlibrary_unix.cpp b/src/corelib/plugin/qlibrary_unix.cpp
index 017aa97b66a..a5c72f81d96 100644
--- a/src/corelib/plugin/qlibrary_unix.cpp
+++ b/src/corelib/plugin/qlibrary_unix.cpp
@@ -123,6 +123,7 @@ QStringList QLibraryPrivate::prefixes_sys()
bool QLibraryPrivate::load_sys()
{
+ QMutexLocker locker(&mutex);
QString attempt;
QFileSystemEntry fsEntry(fileName);
@@ -213,6 +214,7 @@ bool QLibraryPrivate::load_sys()
}
#endif
+ locker.unlock();
bool retry = true;
Handle hnd = nullptr;
for (int prefix = 0; retry && !hnd && prefix < prefixes.size(); prefix++) {
@@ -273,6 +275,8 @@ bool QLibraryPrivate::load_sys()
}
}
#endif
+
+ locker.relock();
if (!hnd) {
errorString = QLibrary::tr("Cannot load library %1: %2").arg(fileName, qdlerror());
}
diff --git a/src/corelib/plugin/qlibrary_win.cpp b/src/corelib/plugin/qlibrary_win.cpp
index 000bf762763..ef58724be8e 100644
--- a/src/corelib/plugin/qlibrary_win.cpp
+++ b/src/corelib/plugin/qlibrary_win.cpp
@@ -78,6 +78,7 @@ bool QLibraryPrivate::load_sys()
// fileName
//
// NB If it's a plugin we do not ever try the ".dll" extension
+ QMutexLocker locker(&mutex);
QStringList attempts;
if (pluginState != IsAPlugin)
@@ -95,6 +96,7 @@ bool QLibraryPrivate::load_sys()
attempts.prepend(QDir::rootPath() + fileName);
#endif
+ locker.unlock();
Handle hnd = nullptr;
for (const QString &attempt : qAsConst(attempts)) {
#ifndef Q_OS_WINRT
@@ -115,6 +117,7 @@ bool QLibraryPrivate::load_sys()
#ifndef Q_OS_WINRT
SetErrorMode(oldmode);
#endif
+ locker.relock();
if (!hnd) {
errorString = QLibrary::tr("Cannot load library %1: %2").arg(
QDir::toNativeSeparators(fileName), qt_error_string());
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