[PATCH STABLE] demandimport: avoid infinite recursion at actual module importing (issue5304)

[FUJIWARA Katsunori]

At Sat, 30 Jul 2016 20:59:05 +0900,
Yuya Nishihara wrote:
> 
> On Sat, 30 Jul 2016 08:24:07 +0900, FUJIWARA Katsunori wrote:
> > # HG changeset patch
> > # User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
> > # Date 1469834098 -32400
> > #      Sat Jul 30 08:14:58 2016 +0900
> > # Branch stable
> > # Node ID b0b24f8a06ffd2ca1dbd798f9c214466889939f8
> > # Parent  491ee264b9f6e32b6e4dfe34180fb48226fc1641
> > demandimport: avoid infinite recursion at actual module importing (issue5304)
> > 
> > Before this patch, importing C module on Windows environment causes
> > infinite recursion call, if py2exe is used with -b2 option.
> > 
> > At importing C module "a.b", extra hooking by zipextimporter of py2exe
> > causes:
> > 
> >   0. assumption before accessing "b" of "a":
> > 
> >      - built-in module object is created for "a",
> >        (= "a" is actually imported)
> >      - _demandmod is created for "a.b" as a proxy object, and
> >        (= "a.b" is not yet imported)
> >      - an attribute "b" of "a" is initialized by the latter
> > 
> >   1. invocation of __import__ via _hgextimport() in _demandmod._load()
> >      for "a.b" implies _demandimport() for "a.b"
> > 
> >      This is unintentional, because _demandmod might be returned by
> >      _hgextimport() instead of built-in module object.
> > 
> >   2. _demandimport() at (1) is invoked with not context of "a", but
> >      context of zipextimporter
> > 
> >      Just after invocation of _hgextimport() in _demandimport(), an
> >      attribute "b" of the built-in module object for "a" is still
> >      bound to the proxy object for "a.b", because context of "a" isn't
> >      updated by actual importing "a.b". even though the built-in
> >      module object for "a.b" already appears in sys.modules.
> > 
> >      Therefore, chainmodules() returns _demandmod for "a.b", which is
> >      gotten from the attribute "b" of "a".
> > 
> >   3. processfromitem() on "a.b" causes _demandmod._load() for "a.b"
> >      again
> > 
> >      _demandimport() takes context of "a" in this case.
> > 
> >      Therefore, attributes below are bound to built-in module object
> >      for "a.b", as expected:
> > 
> >      - "b" of built-in module object for "a"
> >      - _module of _demandmod for "a.b"
> > 
> >   4. but _demandimport() invoked at (1) returns _demandmod object
> > 
> >      because _demandimport() just returns the object returned by
> >      chainmodules() at (3) above.
> > 
> >   5. then, _demandmod._load() causes infinite recursion call
> > 
> >      _demandimport() returns _demandmod for "a.b", and it is "self" at
> >      _demandmod._load().
> > 
> > To avoid infinite recursion at actual module importing, this patch
> > uses self._module, if _hgextimport() returns _demandmod itself. If
> > _demandmod._module isn't yet bound at this point, execution should be
> > aborted, because actual importing failed.
> > 
> > In this patch, _demandmod._module is examined not on _demandimport()
> > side, but on _demandmod._load() side, because:
> > 
> >   - the former has some exit points
> >   - only the latter uses _hgextimport(), except for _demandimport()
> > 
> > BTW, this issue occurs only in the code path for non .py/.pyc files in
> > zipextimporter (strictly speaking, in _memimporter) of py2exe.
> > 
> > Even if zipextimporter is enabled, .py/.pyc files are handled by
> > zipimporter, and it doesn't imply unintentional _demandimport() at
> > invocation of __import__ via _hgextimport().
> 
> Thanks for the detailed investigation. The change looks okay. If new mod is
> self, it should be fine to use self._module.
> 
> A few nits:
> 
> > diff --git a/mercurial/demandimport.py b/mercurial/demandimport.py
> > --- a/mercurial/demandimport.py
> > +++ b/mercurial/demandimport.py
> > @@ -94,6 +94,11 @@ class _demandmod(object):
> >          if not self._module:
> >              head, globals, locals, after, level, modrefs = self._data
> >              mod = _hgextimport(_import, head, globals, locals, None, level)
> > +            if mod is self:
> > +                # see issue5304 for detail
> 
> Can you add more details here?

OK, I'll add "why (1) self._module should be bound to other than self
and (2) subload() and modrefs aren't needed, in this situation" (+
"see also issue5304").


> > +                assert self._module and self._module is not self
> > +                mod = self._module
> 
> Do we need to re-run the setup path of self._module?
> 
> My understanding is that _hgextimport() can recurse into self._load(), in
> which case, subload() and modrefs should already be resolved.

Yes. you are right. _demandmod._load() can return immediately in this
case.

I'll send revised one.

> > +
> >              # load submodules
> >              def subload(mod, p):
> >                  h, t = p, None
> 

----------------------------------------------------------------------
[FUJIWARA Katsunori]                             foozy at lares.dti.ne.jp