Here is the backtrace with line numbers:

qbittorrent: malloc.c:3929: __libc_valloc: Assertion `!p || ((((mchunkptr)((char*)(p) - 2*(sizeof(size_t)))))->size & 0x2) || ar_ptr == (((((mchunkptr)((char*)(p) - 2*(sizeof(size_t)))))->size & 0x4) ? ((heap_info *)((unsigned long)(((mchunkptr)((char*)(p) - 2*(sizeof(size_t))))) & ~((2 * (512 * 1024))-1)))->ar_ptr : &main_arena)' failed.

(gdb) bt 25
#0  0x00ca0422 in __kernel_vsyscall ()
#1  0x006514d1 in *__GI_raise (sig=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#2  0x00654932 in *__GI_abort () at abort.c:92
#3  0x0064a648 in *__GI___assert_fail (
    assertion=0x74bfb0 "!p || ((((mchunkptr)((char*)(p) - 2*(sizeof(size_t)))))->size & 0x2) || ar_ptr == (((((mchunkptr)((char*)(p) - 2*(sizeof(size_t)))))->size & 0x4) ? ((heap_info *)((unsigned long)(((mchunkptr)((char*)("..., 
    file=0x747efe "malloc.c", line=3929, function=0x748250 "__libc_valloc")
    at assert.c:81
#4  0x006966bf in __libc_valloc (bytes=262152) at malloc.c:3928
#5  0x001fcfcd in libtorrent::page_aligned_allocator::malloc (bytes=262152)
    at allocator.cpp:50
#6  0x0022682a in boost::pool<libtorrent::page_aligned_allocator>::ordered_malloc_need_resize (this=0x867cffc) at /usr/include/boost/pool/pool.hpp:461
#7  0x0021f2f6 in boost::pool<libtorrent::page_aligned_allocator>::ordered_malloc (this=0x867ce88, category=0x3cf8d3 "receive buffer")
    at /usr/include/boost/pool/pool.hpp:232
#8  libtorrent::disk_buffer_pool::allocate_buffer (this=0x867ce88, 
    category=0x3cf8d3 "receive buffer") at disk_io_thread.cpp:115
#9  0x002ddd99 in libtorrent::aux::session_impl::allocate_disk_buffer (
    this=0x867cd20, category=0x3cf8d3 "receive buffer")
    at session_impl.cpp:2902
---Type <return> to continue, or q <return> to quit---
#10 0x002ae0a9 in libtorrent::peer_connection::allocate_disk_receive_buffer (
    this=0xb5e2fd60, disk_buffer_size=16384) at peer_connection.cpp:3265
#11 0x0020a555 in libtorrent::bt_peer_connection::on_piece (this=0xb5e2fd60, 
    received=1) at bt_peer_connection.cpp:1129
#12 0x00206778 in libtorrent::bt_peer_connection::dispatch_message (
    this=0xb5e2fd60, received=1) at bt_peer_connection.cpp:1580
#13 0x0020b638 in libtorrent::bt_peer_connection::on_receive (this=0xb5e2fd60, 
    error=..., bytes_transferred=1) at bt_peer_connection.cpp:2924
#14 0x002b631f in libtorrent::peer_connection::on_receive_data (
    this=0xb5e2fd60, error=..., bytes_transferred=5)
    at peer_connection.cpp:4303
#15 0x002bcda2 in boost::asio::detail::handler_queue::handler_wrapper<boost::asio::detail::binder2<libtorrent::peer_connection::allocating_handler<boost::_bi::bind_t<void, boost::_mfi::mf2<void, libtorrent::peer_connection, boost::system::error_code const&, unsigned int>, boost::_bi::list3<boost::_bi::value<boost::intrusive_ptr<libtorrent::peer_connection> >, boost::arg<1>, boost::arg<2> > >, 256u>, boost::system::error_code, unsigned int> >::do_call(boost::asio::detail::handler_queue::handler*) () from /usr/lib/libtorrent-rasterbar.so.6
#16 0x0025890c in boost::asio::detail::task_io_service<boost::asio::detail::epoll_reactor<false> >::run(boost::system::error_code&) ()
   from /usr/lib/libtorrent-rasterbar.so.6
#17 0x002eff6c in boost::asio::io_service::run (this=0x867cd20)
    at /usr/include/boost/asio/impl/io_service.ipp:65
---Type <return> to continue, or q <return> to quit---
#18 libtorrent::aux::session_impl::operator() (this=0x867cd20)
    at session_impl.cpp:2043
#19 0x002fce23 in boost::detail::thread_data<boost::reference_wrapper<libtorrent::aux::session_impl> >::run() () from /usr/lib/libtorrent-rasterbar.so.6
#20 0x005cbc1d in thread_proxy () from /usr/lib/libboost_thread-mt.so.1.38.0
#21 0x00f4f80e in start_thread (arg=0xb6f5cb70) at pthread_create.c:300
#22 0x006f37ee in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130