FCD/Alsa bug (Re: Bug hunting)

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
#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.

Maybe one solution could be to add a function member to mark the
hier_block2 as zombie, the gr_hier_block2 dtor could then cleanup the
map depending on that information.

A workaround could be to catch the exception in fcd_source ctor.
and throw exceptions whenever the fcd C API returns
FCD_MODE_NONE. Well, this is kind of a dirty trick that has lot of
drawbacks.

Maybe some gnuradio gurus could shed some light on how to address this
issue?

Chris

Please find attached the full log.

waited 200 ms for the IO to complete, before it went on to close
same apply for the osmosdr wrapper code.

Chris

//Peter


Christian G.,
Embedded systems engineer.
Techworks Marine
1 Harbour road
Dun Laoghaire
Co. Dublin
Ireland
Tel: + 353 (0) 1 236 5990
Web: http://www.techworks.ie/

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