https://bugs.kde.org/show_bug.cgi?id=515380
Bug ID: 515380
Summary: SMB workers killed during large file transfers causing
40% stall
Classification: Frameworks and Libraries
Product: kio-extras
Version First 25.04.3
Reported In:
Platform: Debian stable
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: Samba
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
Created attachment 189130
--> https://bugs.kde.org/attachment.cgi?id=189130&action=edit
Filtered logs
=== SYSTEM INFORMATION ===
OS: Debian GNU/Linux 13 (trixie)
Kernel: 6.12.63+deb13-amd64
Desktop: KDE Plasma (X11 and Wayland tested)
Dolphin: 25.04.3
kio-extras: 4:25.04.3-1
libsmbclient: 2:4.22.6+dfsg-0+deb13u1
Network: Gigabit Ethernet (Intel igc driver)
=== PROBLEM DESCRIPTION ===
SMB worker processes are killed during large file transfers (>500MB), causing
transfers to fail around 40% completion.
=== REPRODUCTION STEPS ===
1. Open Dolphin
2. Navigate to Network → SMB → any SMB server (tested with multiple Synology
NAS)
3. Attempt to copy a file >500MB from local disk to SMB share
4. Observe transfer behavior
=== OBSERVED BEHAVIOR ===
- Transfer starts at ~10 Mbit/s
- Speed drops to near 0 within seconds
- Progress stalls around 40%
- Multiple SMB workers spawn (6+) and are killed by KIO
- Log shows: "kf.kio.core: killing worker process pid XXXX"
- Followed by: "Socket not connected QLocalSocket::PeerClosedError"
- Then: "An error occurred during write. The worker terminates now."
=== EXPECTED BEHAVIOR ===
File should transfer completely at full network speed.
=== WORKAROUNDS THAT WORK ===
1. Direct smbclient: Transfers complete at 68 MB/s in ~40 seconds
2. CIFS mount in /etc/fstab: Transfers work perfectly at full speed
3. GVFS (Nautilus): Also fails with same symptoms (24 KB/s)
=== ADDITIONAL CONTEXT ===
- Problem appeared after accidental KDE uninstall/reinstall
- Tested on both X11 and Wayland sessions - identical behavior
- Problem occurs with multiple different SMB servers (Synology NAS)
- Network verified working (1 Gbps full duplex, no packet loss)
- Same user account works perfectly from Windows clients
=== CONCLUSION ===
This appears to be a worker management issue in KIO where the framework
incorrectly terminates SMB workers during active transfers, possibly due to
timeout miscalculation or resource limit errors.
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