From bfd3b88bb890460a5b0213258f12e0ab05b84351 Mon Sep 17 00:00:00 2001
From: Christian Kandeler <christian.kandeler@qt.io>
Date: Mon, 3 Jun 2024 13:03:00 +0200
Subject: [PATCH] RemoteLinux: Do not announce connection attempts from non-UI
 threads

This can lead to a deadlock. Example scenario:
  - Have a kit with an unreachable device as the build device.
  - Open a project with a .user file not matching the current QtC.
  - The target setup page will open, showing a candidate widget
    for each kit. These widgets contains path choosers, which nowadays
    start a dedicated thread to validate their input.
  - The path validation thread for the Linux kit arrives at setupShell()
    and tries to announce the connection attempt. To that end, it
    invokes a method of Core::ICore::infoBar, using
    Qt::BlockingQueuedConnection, as otherwise the call would either
    not be tread-safe or arrive too late.
  - As the InfoBar lives in the main thread, control is now passed back
    to that one, and the target setup page continues its work, which is
    to gather candidates for importing a build from. This involves
    perusing potential build directories for all kits. In case of the
    Linux kit, QDirIterator is backed by a remote call to find(), which
    triggers a call to runInShell(), which tries to acquire the mutex
    that is already held by the path validation thread, which in turn is
    waiting for the UI thread.
  - Qt Creator now hangs indefinitely.
Skipping the announcements for non-UI threads limits the usefulness of
this feature, but I don't see a better way.

Change-Id: I816c83358f543aa9a6e6e97eee7fa8ad95e66ea8
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>
---
 src/plugins/remotelinux/linuxdevice.cpp | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/src/plugins/remotelinux/linuxdevice.cpp b/src/plugins/remotelinux/linuxdevice.cpp
index d2779e2ebb8..97cb7f9ae72 100644
--- a/src/plugins/remotelinux/linuxdevice.cpp
+++ b/src/plugins/remotelinux/linuxdevice.cpp
@@ -1231,25 +1231,20 @@ RunResult LinuxDevicePrivate::runInShell(const CommandLine &cmd, const QByteArra
 
 void LinuxDevicePrivate::announceConnectionAttempt()
 {
-    const auto announce = [id = announceId(), name = q->displayName()] {
-        Core::ICore::infoBar()->addInfo(
-            InfoBarEntry(id,
-                         Tr::tr("Establishing initial connection to device \"%1\". "
-                                "This might take a moment.")
-                             .arg(name)));
+    const QString message = Tr::tr("Establishing initial connection to device \"%1\". "
+                                   "This might take a moment.").arg(q->displayName());
+    qCDebug(linuxDeviceLog) << message;
+    if (isMainThread()) {
+        Core::ICore::infoBar()->addInfo(InfoBarEntry(announceId(), message));
         QCoreApplication::processEvents(QEventLoop::ExcludeUserInputEvents);
         QCoreApplication::processEvents(QEventLoop::ExcludeUserInputEvents); // Yes, twice.
-    };
-    if (QThread::currentThread() == qApp->thread())
-        announce();
-    else
-        QMetaObject::invokeMethod(Core::ICore::infoBar(), announce, Qt::BlockingQueuedConnection);
+    }
 }
 
 void LinuxDevicePrivate::unannounceConnectionAttempt()
 {
-    QMetaObject::invokeMethod(Core::ICore::infoBar(),
-                              [id = announceId()] { Core::ICore::infoBar()->removeInfo(id); });
+    if (isMainThread())
+        Core::ICore::infoBar()->removeInfo(announceId());
 }
 
 bool LinuxDevicePrivate::checkDisconnectedWithWarning()