Re: cygwin-1.7.10-1 fork - address space needed by ... already in use

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Feb  7 16:43, Denis Excoffier wrote:
> I've also instrumented cygwin1.dll as suggested recently to Heiko Elger
> in http://cygwin.com/ml/cygwin/2012-02/msg00092.html
> [...]
> - the /proc/<pid>/maps of the processes involved in the fork failure look normal:
> ...
> 61262000-61470000 rw-p 00262000 C095:C492 13792273859134500   /usr/bin/cygwin1.dll
> 674C0000-674C1000 r--p 00000000 C095:C492 2251799814315820    /usr/bin/cygiconv-2.dll
> 674C1000-674D8000 r-xp 00001000 C095:C492 2251799814315820    /usr/bin/cygiconv-2.dll
> 674D8000-675B8000 rw-p 00018000 C095:C492 2251799814315820    /usr/bin/cygiconv-2.dll
> 675B8000-675B9000 r--p 000F8000 C095:C492 2251799814315820    /usr/bin/cygiconv-2.dll
> 675B9000-675BB000 rw-p 000F9000 C095:C492 2251799814315820    /usr/bin/cygiconv-2.dll
> 675BB000-675BC000 r--p 000FB000 C095:C492 2251799814315820    /usr/bin/cygiconv-2.dll
> 6AFC0000-6AFC1000 r--p 00000000 C095:C492 1407374884189126    /usr/bin/cygreadline7.dll
> ...

If this is the map of the forked child, then it's not exactly normal.
Consider that dll_list::reserve_space tries to reserve the memory which
is later supposed to be used for cygiconv-2.dll, but apparently
cygiconv-2.dll is already loaded.

What your report is missing is a bit more information.  We external
observes don't know if the error message in reserve_space actually
reported the address 0x674C0000, and we also don't know if the parent
process has the same layout as the child, or if it's different.  The
above information alone is not enough to evaluate the situation around
cygiconv-2.dll in your scenario.

> Now looking into dll_init.cc, i'm probably going to try the following: if
> VirtualAlloc (line 429, just before 'already occupied') fails, try it
> once more after waiting, say 100ms. Any comments?

Don't, it won't help.  Assuming my above assumptions are correct (but we
need proof), we seem to have a situation like this:

- cygiconv-2.dll has been loaded before cygwin1.dll

- cygwin1.dll tries to reserve space for later loading of cygiconv-2.dll
  but cygiconv-2.dll is already where it belongs.

- Since rsync is linked against cygiconv-2.dll, I'm wondering
  why it's in the list of runtime loaded DLLs.

And, for the records:

- These changes are basically more than 6 months old.  It's really
  frustrating that I never saw this problem even once on one of my test
  machines.  And I still can't.  Can anybody paste a command which fails
  like this into a mail?  If possible, one which is reproducible from
  another machine, like one of mine?


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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