Re: freeze when strace X

From: Thomas Gleixner
Date: Wed Jun 09 2010 - 16:47:39 EST

On Wed, 9 Jun 2010, Matthew Garrett wrote:

> On Wed, Jun 09, 2010 at 10:02:21PM +0200, Ortwin Glück wrote:
> > On 09.06.2010 21:52, Matthew Garrett wrote:
> > > Just to make sure, you're not trying to strace X from within X, are you?
> >
> > Oh... now that you mention it... Is that a silly thing to do?
> > strace X from a different terminal works fine :-)
> >
> > But freezing the system because of that? I mean an error message, log, anything
> > would be "nice".
> strace needs to output text via X, which generates output which needs to
> be output via X... and you'll tend to deadlock. If X is holding any
> interesting kernel locks at that point then it wouldn't surprise me if
> the machine ends up dead.

Nothing to do with kernel locks. strace hooks into the syscall and
intercepts the data, so X is stopped at that point. Now try to send
output to a program which you stopped yourself :)