Re: RFC: nptl threading patch for linux

[Daniel Jacobowitz <drow at mvista dot com>]

On Mon, May 12, 2003 at 03:36:35PM -0400, J. Johnston wrote:
> >
> >I could cause segfaults in both the inferior and GDB, and some missed
> >single-steps.  I don't know if my kernel patch is at fault or your
> >patch, but I figured I'd write them up anyway for posterity and later
> >review.
> >
> >Start with gdb.threads/print-threads.  Put a breakpoint on
> >thread_function and one on the printf ("Done\n") main.  Run, disable
> >the first breakpoint when you hit it, and say next.  You'll hit the
> >breakpoint in main instead of staying within thread_function.
> >
> 
> This does not fail on my test system.  I end up on line 42 after the next
> is issued.

Using 2.5.72 on a single-processor machine, which is what I had lying
around today, I could still reproduce it.  I don't think it's new;
rather, I think it's annoying.

We single-step the thread; because we are not at a breakpoint, since
it's been disabled, all other threads are continued during the
single-step.  The second time we do this, we get a thread creation
event.  GDB proceeds to lose track of the fact that it was
single-stepping, and resumes.

> >In other interesting notes, it looks like there is a (related?) problem
> >with target_thread_alive.  The LWP I'm single-stepping in appears to be
> >marked as not alive about half the time.  No idea what's up with that. 
> >It appears to come from thread_db_thread_alive, not from
> >lin_lwp_thread_alive, which always succeeds.
> >
> >I can't reproduce the SIGSEGV now for some reason.
> >
> 
> Have you managed to trace which test in thread_db_alive is returning false?

It may have been my imagination.  Now all appears well.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer