Question

我正在尝试建立多个ssh连接（使用libssh 0.7.5），并使用boost :: threads将它们并行化。

在并行化时，我观察到可执行文件的20个执行中有3个由于glibc“双重释放或损坏”错误而失败，而2个由于分段错误而失败。

尝试进行串行ssh连接调用时未观察到这些错误。

使用gdb作为调试工具，我发现下面的回溯引起了问题：

#0  0x00007ffff49735e5 in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#1  0x00007ffff4974dc5 in abort () at abort.c:92
#2  0x00007ffff49b14f7 in __libc_message (do_abort=2, fmt=0x7ffff4a99a60 "*** glibc detected *** %s: %s: 0x%s ***\n")
   at ../sysdeps/unix/sysv/linux/libc_fatal.c:198
#3  0x00007ffff49b6f3e in malloc_printerr (action=3, str=0x7ffff4a99df0 "double free or corruption (!prev)",
   ptr=<value optimized out>, ar_ptr=<value optimized out>) at malloc.c:6360
#4  0x00007ffff49b9dd0 in _int_free (av=0x7fffe0000020, p=0x7fffe0001810, have_lock=1) at malloc.c:4846
#5  0x00007ffff49bcd60 in _int_realloc (av=0x7fffe0000020, oldp=0x7fffe0001810, oldsize=<value optimized out>, nb=272)
   at malloc.c:5398
#6  0x00007ffff49bd058 in __libc_realloc (oldmem=0x7fffe0001820, bytes=256) at malloc.c:3833
#7  0x00007ffff6f06ccf in CRYPTO_realloc () from /usr/lib64/libcrypto.so.10
#8  0x00007ffff6f822be in lh_insert () from /usr/lib64/libcrypto.so.10
#9  0x00007ffff6f09d9b in OBJ_NAME_add () from /usr/lib64/libcrypto.so.10
#10 0x00007ffff6f914e7 in OpenSSL_add_all_ciphers () from /usr/lib64/libcrypto.so.10
#11 0x00007ffff6f911ae in OPENSSL_add_all_algorithms_noconf () from /usr/lib64/libcrypto.so.10
#12 0x00007ffff7b69c8a in ssh_crypto_init () from /home/utils/libssh-0.7.5/lib/libssh.so.4
#13 0x00007ffff7b6ae05 in ssh_init () from /home/utils/libssh-0.7.5/lib/libssh.so.4
#14 0x00007ffff7b65799 in ssh_connect () from /home/utils/libssh-0.7.5/lib/libssh.so.4
#15 0x000000000043f766 in SSHConnector::SSHConnector(std::basic_string<char, std::char_traits<char>, std::allocator<char> >) () at SSHConnector.cpp:44
#16 0x0000000000433855 in connect_host(connect_host_report*) () at Util.cpp:339
#17 0x000000000043f57d in void boost::_bi::list1<boost::_bi::value<connect_host_report*> >::operator()<void (*)(connect_host_report*), boost::_bi::list0>(boost::_bi::type<void>, void (*&)(connect_host_report*), boost::_bi::list0&, int)
   () at /home/utils/boost-1.55.0//include/boost/bind/bind.hpp:253
#18 0x000000000043f0f9 in boost::_bi::bind_t<void, void (*)(connect_host_report*), boost::_bi::list1<boost::_bi::value<connect_host_report*> > >::operator()() () at /home/utils/boost-1.55.0//include/boost/bind/bind_template.hpp:20
#19 0x000000000043e738 in boost::detail::thread_data<boost::_bi::bind_t<void, void (*)(connect_host_report*), boost::_bi::list1<boost::_bi::value<connect_host_report*> > > >::run() ()
   at /home/utils/boost-1.55.0//include/boost/thread/detail/thread.hpp:117
#20 0x00007ffff60995da in thread_proxy () from /home/utils/boost-1.55.0//lib/libboost_thread.so.1.55.0
#21 0x00007ffff6c86aa1 in start_thread (arg=0x7ffff1593700) at pthread_create.c:301
#22 0x00007ffff4a29aad in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115

还要从SSHConnector粘贴相关代码（第44行ssh_connect是erro的来源 r）

 28                 string error_info;


 29 
 30                 ssh_session_object = ssh_new();
 31                 if (ssh_session_object == NULL) {
 32                         error_info = "Could not create SSH session";
 33                         throw ConnectionUnsuccessfulException(hostname, error_info,
 34                                         CLEANUP_NOT_REQUIRED);
 35                 }
 36 
 37                 ssh_options_set(ssh_session_object, SSH_OPTIONS_HOST, hostname.c_str());
 38                 ssh_options_set(ssh_session_object, SSH_OPTIONS_LOG_VERBOSITY,
 39                                 &verbosity);
 40                 ssh_options_set(ssh_session_object, SSH_OPTIONS_TIMEOUT,
 41                                 &ssh_connection_timeout);
 42 
 43                 int rc;
 44                 rc = ssh_connect(ssh_session_object);

还尝试了valgrind的测试：

==641== 
==641== HEAP SUMMARY:
==641==     in use at exit: 16,104 bytes in 540 blocks
==641==   total heap usage: 4,791 allocs, 4,251 frees, 559,189 bytes allocated
==641== 
==641== Searching for pointers to 540 not-freed blocks
==641== Checked 1,006,816 bytes
==641== 
==641== LEAK SUMMARY:
==641==    definitely lost: 0 bytes in 0 blocks
==641==    indirectly lost: 0 bytes in 0 blocks
==641==      possibly lost: 0 bytes in 0 blocks
==641==    still reachable: 16,104 bytes in 540 blocks
==641==         suppressed: 0 bytes in 0 blocks
==641== Rerun with --leak-check=full to see details of leaked memory
==641== 
==641== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 6)
--641-- 
--641-- used_suppression:      4 U1004-ARM-_dl_relocate_object
--641-- used_suppression:      2 glibc-2.5.x-on-SUSE-10.2-(PPC)-2a
==641== 
==641== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 6)

有人可以建议导致此错误的随机行为的原因吗？

Answer 1

1.1之前的OpenSSL版本不是线程安全的，除非应用程序注册了自己的锁定回调。 ssh_init提供了一组默认的锁定回调，但是其初始化序列本身不是线程安全的（在版本0.7中），因此必须显式调用ssh_threads_init或inner join以避免竞争条件

使用线程并行化ssh调用的malloc问题

1 个答案: