Strange segfault

Alexey Volkov

I'm facing a strange segfault in our production environment which cannot be reproduced on the development machine. I have implemented backtrace and signal 11 handler to see what is happening, but it gives more questions then answers. It is a QTcpServer backend, and the segfault happens in QIODevice::channelBytesWritten in Qt internals, several seconds(!!!) after the last networking activity. No disconnects were detected, none of my code is in a scope, just system calls and Qt internals. Here is the trace

24.03.2023 03:25:43.915 2 CRITICAL 140690302428736 Ooops: signal 11 - Segmentation fault
24.03.2023 03:25:43.915 2 CRITICAL 140690302428736
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [1] /lib64/libpthread.so.0(+0x13a20) [0x7ff50ca12a20]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [2] /lib64/libQt5Core.so.5(+0x2d9ebf) [0x7ff50cd80ebf]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [3] /lib64/libQt5Core.so.5(_ZN9QIODevice19channelBytesWrittenEix+0x51) [0x7ff50cc9d231]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [4] /lib64/libQt5Network.so.5(+0x10294c) [0x7ff50d1c194c]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [5] /lib64/libQt5Network.so.5(+0x111f9f) [0x7ff50d1d0f9f]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [6] /lib64/libQt5Core.so.5(_ZN16QCoreApplication15notifyInternal2EP7QObjectP6QEvent+0x10b) [0x7ff50cd4d7bb]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [7] /lib64/libQt5Core.so.5(+0x2f863f) [0x7ff50cd9f63f]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [8] /lib64/libglib-2.0.so.0(g_main_context_dispatch+0x19f) [0x7ff50bb704cf]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [9] /lib64/libglib-2.0.so.0(+0xa94f8) [0x7ff50bbc44f8]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [10] /lib64/libglib-2.0.so.0(g_main_context_iteration+0x33) [0x7ff50bb6dc03]
24.03.2023 03:25:43.916 2 CRITICAL 140690302428736 [11] /lib64/libQt5Core.so.5(_ZN20QEventDispatcherGlib13processEventsE6QFlagsIN10QEventLoop17ProcessEventsFlagEE+0x68) [0x7ff50cd9ebb8]
24.03.2023 03:25:43.917 2 CRITICAL 140690302428736 [12] /lib64/libQt5Core.so.5(_ZN10QEventLoop4execE6QFlagsINS_17ProcessEventsFlagEE+0x132) [0x7ff50cd4c1e2]
24.03.2023 03:25:43.917 2 CRITICAL 140690302428736 [13] /lib64/libQt5Core.so.5(_ZN7QThread4execEv+0xaa) [0x7ff50cb8f2ca]
24.03.2023 03:25:43.917 2 CRITICAL 140690302428736 [14] /lib64/libQt5Core.so.5(+0xe94c6) [0x7ff50cb904c6]
24.03.2023 03:25:43.917 2 CRITICAL 140690302428736 [15] /lib64/libpthread.so.0(+0x92a5) [0x7ff50ca082a5]
24.03.2023 03:25:43.917 2 CRITICAL 140690302428736 [16] /lib64/libc.so.6(clone+0x43) [0x7ff50c5b0323]
24.03.2023 03:25:43.917 2 CRITICAL 140690302428736
24.03.2023 03:25:43.917 2 CRITICAL 140690302428736 Happy debugging!

The names are not de-mangled correctly, but still readable.
Any idea?

J.Hilk

@Alexey-Volkov

I had this happening in the past, was the result of a too old Qt Version and a to new Windows version.

Updating the Qt Libs to the latest available fixed that

Alexey Volkov

@J-Hilk Thank you for response!
It is Qt 5.15.2 in Fedora34 container, is it really too old?

J.Hilk

@Alexey-Volkov I had the issue with 5.15.9 on windows 11, needed to upgrade to 5.15.13...

the last precompiled 5.15.2 is super old :D, I would consider upgrading or at least recompiling yourself with the latest OS sdks

Alexey Volkov

@J-Hilk wow, thank you for giving me a hope! :)
I will recompile it. Which is the last stable version of 5.15?

J.Hilk

@Alexey-Volkov tough, the latest official one is 5.15.13 but that is for commercial users only, the open source variant is delayed by a significant amount of time.

The latest one I found is 5.15.6
https://lists.qt-project.org/pipermail/development/2022-September/042937.html

maybe 5.15.7 is also released, not sure.

Open source Qt6 is always up to date with the commercial one

Alexey Volkov

@J-Hilk any chance to get patch for this issue? I would apply it to my build

Alexey Volkov

@J-Hilk
which OpenSSL is used in Qt6?

J.Hilk

@Alexey-Volkov said in Strange segfault:

any chance to get patch for this issue? I would apply it to my build

not sure, don't think, so, it will be released, but its time gated

which OpenSSL is used in Qt6?

I think OpenSSL3 v6.2.0