dlclose() vs fork()

dlclose() vs fork()

[Alexey Sokolov]

Hello,
If the same DLL is dlopen()ed several times, dlclose() will actually
unload the DLL only after the same number of calls to dlclose().

This works fine in cygwin, until we add fork().

It looks like in the child process the counters of inherited DLLs are
set to 1, so the first dlclose() unloads it, causing segfault for
subsequent access to the unloaded code.
https://github.com/znc/znc/issues/1385#issuecomment-288014319 has a
working minimal example of this behavior.

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Re: dlclose() vs fork()

[Corinna Vinschen]

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On Mar 21 09:03, Alexey Sokolov wrote:
> Hello,
> If the same DLL is dlopen()ed several times, dlclose() will actually
> unload the DLL only after the same number of calls to dlclose().
> 
> This works fine in cygwin, until we add fork().
> 
> It looks like in the child process the counters of inherited DLLs are
> set to 1, so the first dlclose() unloads it, causing segfault for
> subsequent access to the unloaded code.
> https://github.com/znc/znc/issues/1385#issuecomment-288014319 has a
> working minimal example of this behavior.

dlopen/dlclose reference counting was broken.  I applied a fix and
uploaded new dev snapshots to https://cygwin.com/snapshots/

I'm just building a 2.8.0-0.2 test release as well.


Please test.


Thanks,
Corinna

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Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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Re: dlclose() vs fork()

[Alexey Sokolov]

Thanks Corinna for the quick fix,
The user confirmed it's working now with the snapshot.

21.03.2017 13:42, Corinna Vinschen пишет:
> On Mar 21 09:03, Alexey Sokolov wrote:
>> Hello,
>> If the same DLL is dlopen()ed several times, dlclose() will actually
>> unload the DLL only after the same number of calls to dlclose().
>>
>> This works fine in cygwin, until we add fork().
>>
>> It looks like in the child process the counters of inherited DLLs are
>> set to 1, so the first dlclose() unloads it, causing segfault for
>> subsequent access to the unloaded code.
>> https://github.com/znc/znc/issues/1385#issuecomment-288014319 has a
>> working minimal example of this behavior.
>
> dlopen/dlclose reference counting was broken.  I applied a fix and
> uploaded new dev snapshots to https://cygwin.com/snapshots/
>
> I'm just building a 2.8.0-0.2 test release as well.
>
>
> Please test.
>
>
> Thanks,
> Corinna
>


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Re: dlclose() vs fork()

[Corinna Vinschen]

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On Mar 22 08:44, Alexey Sokolov wrote:
> Thanks Corinna for the quick fix,
> The user confirmed it's working now with the snapshot.
> 
> 21.03.2017 13:42, Corinna Vinschen пишет:
> > On Mar 21 09:03, Alexey Sokolov wrote:
> > > Hello,
> > > If the same DLL is dlopen()ed several times, dlclose() will actually
> > > unload the DLL only after the same number of calls to dlclose().
> > > 
> > > This works fine in cygwin, until we add fork().
> > > 
> > > It looks like in the child process the counters of inherited DLLs are
> > > set to 1, so the first dlclose() unloads it, causing segfault for
> > > subsequent access to the unloaded code.
> > > https://github.com/znc/znc/issues/1385#issuecomment-288014319 has a
> > > working minimal example of this behavior.
> > 
> > dlopen/dlclose reference counting was broken.  I applied a fix and
> > uploaded new dev snapshots to https://cygwin.com/snapshots/

Thanks for testing and feedback.


Corinna

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

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