coredump with calloc()

Program terminated with signal 11, Segmentation fault.
#0  0x0e0ec2e8 in malloc_consolidate () from /lib/libc.so.6
#1  0x0e0ef21c in _int_malloc () from /lib/libc.so.6
#2  0x0e0f078c in calloc () from /lib/libc.so.6

用valgrind的memcheck检测到有个内存malloc后free了两次，导致再次分配内存就会coredump.