Re: [Discuss-gnuradio] FCD/Alsa bug (Re: Bug hunting)

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----- Reply message -----
From: "Christian Gagneraud" <address@hidden>
To: "Dimitri Stolnikov" <address@hidden>
Cc: <address@hidden>, <address@hidden>
Subject: [Discuss-gnuradio] FCD/Alsa bug (Re: Bug hunting)
Date: Wed, Aug 8, 2012 9:02 am


Cross posting to discuss-gnuradio.

The bug in question is that if you instanciate an alsa source on a busy device (opened by another app), then the program crashed.

On 08/08/12 00:23, Dimitri Stolnikov wrote:
> Hi Christian,
[...]
>
> The other problem (segfault on trow in ctor) still has to be addressed.

Yes, I started to investigate, and it seems to me that this is not a gr-osmosdr bug, but it's a gnuradio one, caused by gr-fcd.

This simple test program have the same problem, yet it only uses gr-fcd.

#include <iostream>
#include <fcd_source_c.h>
int main(int argc, char **argv)
{
    fcd_source_c_sptr fsrc;
    try {
	fsrc = fcd_make_source_c("hw:2"); // KO, from gr-fcd
    }
    catch (std::runtime_error &e) {
	std::cerr << "Error!\n";
    }
    exit(0);
}

g++ test.cc -o test -I/usr/local/include/gnuradio -lgnuradio-fcd

Here is the log:
audio_alsa_source[hw:2]: Device or resource busy
Error!
*** glibc detected *** /home/cgagneraud/sdr/gr-osmosdr/test: free(): invalid pointer: 0x08052e3c ***
[...]

And here is a cleaned up backtrace:
operator delete
gruel::msg_accepter::~msg_accepter
checked_delete<gr_hier_block2>
boost::detail::sp_counted_impl_p<gr_hier_block2>::dispose
[...]
const, boost::shared_ptr<gr_basic_block> > > >::~map
__cxa_finalize
__do_global_dtors_aux
[...]
main

The problem is related to gnuradio-core/src/lib/runtime/gr_sptr_magic.{h,cc} and the static std::map in there.

gr_hier_block2 ctor insert "this" in this map, but then in fcd_source ctor, audio_alsa_source ctor throws an exception, so "this" (gr_hier_block2/fcd_source) is not a valid pointer anymore.
When the program exits, the map get cleanup up and free is called on this pointer.

It's not possible to cleanup the map in fcd_source, because the dtor is not called when exception occurs in the ctor (which, btw, leads to some memory leaks in alsa_source: namely d_hw_params and d_sw_params).
It's a bad idea to call fetch_initial_sptr(this) before throwing in the ctor, because it seems the object get deleted.