Bug 243534

Summary:	Strace hangs system
Product:	[Fedora] Fedora	Reporter:	Tim Niemueller <tim>
Component:	kernel	Assignee:	Roland McGrath <roland>
Status:	CLOSED NOTABUG	QA Contact:	Brian Brock <bbrock>
Severity:	high	Docs Contact:
Priority:	medium
Version:	7	CC:	jan.kratochvil
Target Milestone:	---
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2007-09-10 07:33:12 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Tim Niemueller 2007-06-09 15:00:16 UTC

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).

Comment 1 Roland McGrath 2007-08-02 05:44:30 UTC

Can you reproduce this with a more recent F7 update kernel?

Comment 2 Tim Niemueller 2007-08-03 10:59:22 UTC

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().

Comment 3 Roland McGrath 2007-09-10 07:33:12 UTC

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.