Red Hat Bugzilla – Bug 243534
Strace hangs system
Last modified: 2007-11-30 17:12:07 EST
Description of problem: I tried to strace nm-vpn-properties to see why vpnc could not be loaded, this made my system (Thinkpad T60, Core 2 Duo) freeze. I could still move the mouse cursor, but the machine would not react to clicks or keyboard input, the clock in the panel stops. Version-Release number of selected component (if applicable): kernel-2.6.21-1.3219.fc7 kernel-2.6.21-1.3224.fc7 strace-4.5.15-1.fc7 How reproducible: Always Steps to Reproduce: 1. strace nm-vpn-properties 2. See system freeze Actual results: System freezes Expected results: strace output of process. Additional info: I have tested both mentioned kernels, the freeze seems to happen at different times in the running strace (the last strace output was different on several tries).
Can you reproduce this with a more recent F7 update kernel?
Yes, I have just tried it and it still happens, versions: # rpm -q kernel strace kernel-2.6.22.1-29.fc7 kernel-2.6.22.1-41.fc7 strace-4.5.15-1.fc7 Kernel 2.6.22.1-41.fc7 is currently running. The last console output was a call to poll().
I think I reproduced what you saw, but I didn't see any evidence of any system-wide bug. That is, the whole X session did indeed stop responding so that only the X server itself responded (mouse movement, hot keys to switch VTs). The system overall was fine, and I was able to use it remotely or from another VT no problem. From there I saw strace blocked in doing output to its stdout, i.e. the pty to the gnome-terminal in my X session. I imagine that nm-vpn-properties is in the middle of some X operation that grabs the server or something or other. As soon as nm-vpn-properties resumes running, everything updates normally (and even processes some mouse clicks I did while it was "frozen"). But strace won't let nm-vpn-properties resume until it finishes writing to stdout; that write call is blocked waiting for gnome-terminal to read from the pty; gnome-terminal is blocked waiting for the X server; the X server is not responding because nm-vpn-properties is in the middle of something. So, deadlock. Using "strace -o log nm-vpn-properties", nothing funny happens.