[PATCH] RFC: do not detach when we think tracee is going to die

[Denys Vlasenko]

On Wed, 2011-08-17 at 14:45 +0400, Dmitry V. Levin wrote:
> On Mon, Aug 15, 2011 at 12:01:56PM +0200, Denys Vlasenko wrote:
> > On Tue, 2011-08-02 at 01:45 +0400, Dmitry V. Levin wrote:
> > > On Sat, Jun 25, 2011 at 11:34:23AM +0200, Denys Vlasenko wrote:
> [...]
> > > > I need to look in the past to figure out why we even do it.
> > > > First guess is that it's a workaround for old kernel bugs.
> > > 
> > > How old those buggy kernels might be?
> > 
> > The internal_exit function, whose reason for existence is to 
> > support "detach on exit" behavior, is from 1995.
> > 
> > I tried to test whether this is still needed on kernel 2.4.20,
> > but this kernel oopses (somewhere in ptrace_check_attach).
> 
> I tried to test current strace with linux-2.4.32-ow1 from
> ftp://ftp.openwall.com/pub/Owl/2.0-release/iso/Owl-2.0-release-i386.iso.gz
> where PTRACE_SETOPTIONS are certainly not supported, and found out that
> test_ptrace_setoptions_followfork() fails to wait for all child processes
> it generates, resulting to an unexpected wait failure later in
> test_ptrace_setoptions_for_all().
> 
> I've just pushed a fix to
> http://strace.git.sourceforge.net/git/gitweb.cgi?p=strace/strace;a=commitdiff;h=ldv/PTRACE_SETOPTIONS-tests
> please have a look.

Took a look. It's not readily apparent where the fix is,
but I trust that you tested it :)


> With the fix, at least simple strace -f test works on linux-2.4.32.
> There are no kernel oopses there, but ./strace -f ./test/childthread
> outputs something different from expected.
>
> > Do you think it would be better if we recommend users of
> > 2.4 kernels to simply stick with older strace versions?
> 
> Do we have an alternative choice now?

Alternative choice is to test/fix our current code at least on the
latest 2.4.x, but I don't have suitable test environment with 2.4
kernels. A qemu image would be ideal...

-- 
vda