0x000000BFBSODCritical

0x000000BF — Mutex Already Owned | Blue Screen Fix Guide

MUTEX_ALREADY_OWNED

Windows XPWindows VistaWindows 7Windows 8Windows 10Windows 11

What Does 0x000000BF Mean?

A thread attempted to acquire a mutex that it already owned without using recursive acquisition.

Real-World Causes

1Driver deadlock bug
2Re-entrant code acquiring same mutex
3Kernel synchronization error

Symptoms

⚠Blue screen with stop code MUTEX_ALREADY_OWNED
⚠System reboots unexpectedly
⚠Possible data loss from unsaved work

DIY Fix

Beginner-friendly steps you can try at home

1Restart your computer
2Run System File Checker (sfc /scannow)
3Check Windows Update
4Run DISM /Online /Cleanup-Image /RestoreHealth

Advanced Fix

For experienced users and IT professionals

1Analyze minidump with WinDbg
2Check Event Viewer for correlated errors
3Use Process Monitor to trace system activity
4Perform clean boot to isolate the cause

Frequently Asked Questions

What causes MUTEX_ALREADY_OWNED?

A thread attempted to acquire a mutex that it already owned without using recursive acquisition.

Can I fix Mutex Already Owned myself?

In many cases yes. Start with basic troubleshooting like restarting, updating drivers, and running System File Checker. If the issue persists, advanced analysis of crash dumps may be needed.

Related Error Codes

0x00000011Thread not Mutex Owner 0x0000000DMutex Level Number Violation

About the Author

Windows Troubleshooting Team

Verified against official Microsoft documentation and real-world diagnostic data. Error behavior confirmed across Windows 10, Windows 11, and Windows Server.