bt output :
#0  0x0808086e in ast_channel_spy_read_frame (spy=0x2f29fd0, samples=0) at channel.c:4729
#1  0x00daf947 in spy_generate (chan=0xb7b18d68, data=0x2f29fd0, len=0, samples=0) at app_chanspy.c:172
#2  0x0807e1ac in ast_read_generator_actions (chan=0xb7b18d68, f=0x8150b40) at channel.c:2164
#3  0x080845a4 in __ast_read (chan=0xb7b18d68, dropaudio=0) at channel.c:2517
#4  0x00dafca4 in channel_spy (chan=0xb7b18d68, spyee=0xb7b169c8, volfactor=0x2f2a3b0, fd=0, flags=0x2f2a424) at app_chanspy.c:327
#5  0x00db0525 in common_exec (chan=0xb7b18d68, flags=0x2f2a424, volfactor=0, fd=0, mygroup=0x0,
    spec=0x2f2a3d0 "SIP/1003_cci09-b7b31530", exten=0x0, context=0x0) at app_chanspy.c:532
#6  0x00db0bd3 in chanspy_exec (chan=0xb7b18d68, data=0x2f2a9cd) at app_chanspy.c:635
#7  0x080bf5df in pbx_exec (c=0xb7b18d68, app=0x962efe8, data=0x2f2a9cd) at pbx.c:532
#8  0x00e153d1 in handle_exec (chan=0x0, agi=0x0, argc=3, argv=0x2f2a7c0) at res_agi.c:1111
#9  0x00e17567 in agi_exec_full (chan=0xb7b18d68, data=Variable "data" is not available.
) at res_agi.c:1808
#10 0x080ca371 in pbx_extension_helper (c=0xb7b18d68, con=Variable "con" is not available.
) at pbx.c:532
#11 0x080cb6bf in __ast_pbx_run (c=0xb7b18d68) at pbx.c:2288
#12 0x080cd63e in pbx_thread (data=0xb7b18d68) at pbx.c:2603
#13 0x080fb4d5 in dummy_start (data=0x39) at utils.c:793
#14 0x003f23cc in start_thread () from /lib/tls/libpthread.so.0
#15 0x00305c3e in clone () from /lib/tls/libc.so.6

bt full output :
#0  0x0808086e in ast_channel_spy_read_frame (spy=0x2f29fd0, samples=0) at channel.c:4729
        result = Variable "result" is not available.

channel.c Line 4729  :
4729            if ((AST_LIST_FIRST(&spy->read_queue.list)->samples == samples) &&