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Re: Infinite loop with concurrent ssh_connect() on CentOS 6
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- Subject: Re: Infinite loop with concurrent ssh_connect() on CentOS 6
- From: Doug Judd <doug@xxxxxxxxxxxxxx>
- Reply-to: libssh@xxxxxxxxxx
- Date: Tue, 28 Oct 2014 15:50:22 -0700
- To: libssh@xxxxxxxxxx
Correct me if I'm wrong, but looking at the verbose build output, it looks like the only difference between libssh.so and libssh_threads.so is that the latter includes thread/pthread.c. pthread.c looks like the threading hooks for pthreads. Since I've implemented my own threading hooks, I think I should be ok just linking with libssh.so. Does this sound correct to you? On Tue, Oct 28, 2014 at 3:33 PM, Doug Judd <doug@xxxxxxxxxxxxxx> wrote: > Hi Aris, > > Thanks for the reply. I did read that section, but I may have > mis-interpreted it. My understanding is that I only need to link with > libssh_threads if using pthreads. Since my application uses Boost threads > and C++11 threads, I assumed that I was not using pthreads, so I followed > the advice of bullet point #3 and implemented my own threading hooks and > did not link with libssh_threads. However, grep'ing through the boost > header files, there are over 500 lines that reference pthread, so maybe > Boost threads use pthreads under-the-hood. What do you recommend for my > situation (combination of Boost threads and C++11 threads)? Do I still > need to link with libssh_threads, or is implementing my own threading hooks > sufficient? > > - Doug > > > On Tue, Oct 28, 2014 at 2:12 PM, Aris Adamantiadis <aris@xxxxxxxxxxxx> > wrote: > >> Le 28/10/14 17:12, Doug Judd a écrit : >> > It looks like I can get around this last problem by calling ssh_init() >> > in the beginning of the program before spawning any threads. From an >> > API design standpoint, however, if a call to ssh_init() is >> > prerequisite for calling ssh_connect() concurrently, then >> > ssh_connect() should verify that ssh_init() has been called. If it >> > hasn't been called it should fail with an informative error >> code/message. >> > >> > - Doug >> Hi Doug, >> >> Thanks for your feedback. >> While this could be a solution, 99% of developers using libssh are not >> using threads and this issue is already extensively covered in the >> documentation (http://api.libssh.org/master/libssh_tutor_threads.html). >> Calling ssh_init() in the beginning of your program is not enough, you >> must explicitly link with libssh_threads & us ssh_threads_set_callbacks >> or implement your own threading hooks. >> I have looked at other alternatives, like doing this automatically, and >> they were not satisfying in a performance/dependency point of view. We >> basically copied the libcrypto model (with providing a shared lib for >> pthread for convenience). >> >> Regards, >> >> Aris >> >> > >> > >> > On Tue, Oct 28, 2014 at 8:36 AM, Doug Judd <doug@xxxxxxxxxxxxxx >> > <mailto:doug@xxxxxxxxxxxxxx>> wrote: >> > >> > Here's another infinite loop problem when calling ssh_connect() >> > concurrently. This time it looks like it's in the libcrypto >> > initialization code: >> > >> > Thread 13 (Thread 0x7f833a002700 (LWP 24506)): >> > #0 0x00007f83420af3e9 in lh_insert () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #1 0x00007f834200e7e5 in OBJ_NAME_add () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #2 0x00007f83420c0176 in OpenSSL_add_all_ciphers () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #3 0x00007f83420bfd0e in OPENSSL_add_all_algorithms_noconf () >> > from /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #4 0x00007f8342675515 in ssh_crypto_init () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #5 0x00007f83426776a2 in ssh_init () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #6 0x00007f8342673929 in ssh_connect () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #7 0x0000000000435614 in >> > Hypertable::SshSocketHandler::handle(int, int) () >> > #8 0x0000000000484efa in >> > Hypertable::IOHandlerRaw::handle_event(epoll_event*, long) () >> > #9 0x0000000000492e24 in Hypertable::ReactorRunner::operator()() () >> > #10 0x00007f83415bace3 in thread_proxy () from >> > /opt/hypertable/doug/0.9.8.3/lib/libboost_thread.so.1.54.0 >> > <http://0.9.8.3/lib/libboost_thread.so.1.54.0> >> > #11 0x0000003ee42077f1 in start_thread () from >> /lib64/libpthread.so.0 >> > #12 0x0000003ee3ae5ccd in clone () from /lib64/libc.so.6 >> > Thread 12 (Thread 0x7f8339601700 (LWP 24507)): >> > #0 0x00007f83420af3e9 in lh_insert () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #1 0x00007f834200e7e5 in OBJ_NAME_add () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #2 0x00007f83420c0176 in OpenSSL_add_all_ciphers () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #3 0x00007f83420bfd0e in OPENSSL_add_all_algorithms_noconf () >> > from /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #4 0x00007f8342675515 in ssh_crypto_init () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #5 0x00007f83426776a2 in ssh_init () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #6 0x00007f8342673929 in ssh_connect () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #7 0x0000000000435614 in >> > Hypertable::SshSocketHandler::handle(int, int) () >> > #8 0x0000000000484efa in >> > Hypertable::IOHandlerRaw::handle_event(epoll_event*, long) () >> > #9 0x0000000000492e24 in Hypertable::ReactorRunner::operator()() () >> > #10 0x00007f83415bace3 in thread_proxy () from >> > /opt/hypertable/doug/0.9.8.3/lib/libboost_thread.so.1.54.0 >> > <http://0.9.8.3/lib/libboost_thread.so.1.54.0> >> > #11 0x0000003ee42077f1 in start_thread () from >> /lib64/libpthread.so.0 >> > #12 0x0000003ee3ae5ccd in clone () from /lib64/libc.so.6 >> > Thread 11 (Thread 0x7f8338c00700 (LWP 24508)): >> > #0 0x00007f83420af3e9 in lh_insert () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #1 0x00007f834200e7e5 in OBJ_NAME_add () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #2 0x00007f83420c0176 in OpenSSL_add_all_ciphers () from >> > /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #3 0x00007f83420bfd0e in OPENSSL_add_all_algorithms_noconf () >> > from /opt/hypertable/doug/0.9.8.3/lib/libcrypto.so.1.0.0 >> > <http://0.9.8.3/lib/libcrypto.so.1.0.0> >> > #4 0x00007f8342675515 in ssh_crypto_init () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #5 0x00007f83426776a2 in ssh_init () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #6 0x00007f8342673929 in ssh_connect () from >> > /opt/hypertable/doug/0.9.8.3/lib/libssh.so.4 >> > <http://0.9.8.3/lib/libssh.so.4> >> > #7 0x0000000000435614 in >> > Hypertable::SshSocketHandler::handle(int, int) () >> > #8 0x0000000000484efa in >> > Hypertable::IOHandlerRaw::handle_event(epoll_event*, long) () >> > #9 0x0000000000492e24 in Hypertable::ReactorRunner::operator()() () >> > #10 0x00007f83415bace3 in thread_proxy () from >> > /opt/hypertable/doug/0.9.8.3/lib/libboost_thread.so.1.54.0 >> > <http://0.9.8.3/lib/libboost_thread.so.1.54.0> >> > #11 0x0000003ee42077f1 in start_thread () from >> /lib64/libpthread.so.0 >> > #12 0x0000003ee3ae5ccd in clone () from /lib64/libc.so.6 >> > ... >> > >> > The process is stuck at 100% CPU utilization. The version of >> > openssl that the program is linked with is 1.0.2-beta3. >> > >> > - Doug >> > >> > >> > On Tue, Oct 21, 2014 at 10:32 AM, Doug Judd <doug@xxxxxxxxxxxxxx >> > <mailto:doug@xxxxxxxxxxxxxx>> wrote: >> > >> > I'm developing a multi-host ssh tool using libssh 0.6.3. The >> > tool establishes connections asynchronously and in parallel. >> > Intermittently, the tool will get stuck in a busy loop with a >> > stack trace such as the following: >> > >> > Thread 13 (Thread 0x7f65f9b41700 (LWP 13549)): >> > #0 0x0000003ee3adc613 in poll () from /lib64/libc.so.6 >> > #1 0x0000003ee3b0fe3c in clntudp_call () from /lib64/libc.so.6 >> > #2 0x0000003ee76058bb in do_ypcall () from /lib64/libnsl.so.1 >> > #3 0x0000003ee76060ab in yp_match () from /lib64/libnsl.so.1 >> > #4 0x00007f65f1f14f79 in _nss_nis_getpwuid_r () from >> /lib64/libnss_nis.so.2 >> > #5 0x0000003ee3aaa4ed in getpwuid_r@@GLIBC_2.2.5 () from >> /lib64/libc.so.6 >> > #6 0x00007f6601b0152e in ssh_path_expand_tilde () from >> /opt/hypertable/doug/0.9.8.2/lib/libssh.so.4 >> > #7 <http://0.9.8.2/lib/libssh.so.4#7> 0x00007f6601b02bc3 in >> ssh_options_set () from /opt/hypertable/doug/0.9.8.2/lib/libssh.so.4 >> > #8 <http://0.9.8.2/lib/libssh.so.4#8> 0x00007f6601b036fb in >> ssh_options_apply () from /opt/hypertable/doug/0.9.8.2/lib/libssh.so.4 >> > #9 <http://0.9.8.2/lib/libssh.so.4#9> 0x00007f6601af68fe in >> ssh_connect () from /opt/hypertable/doug/0.9.8.2/lib/libssh.so.4 >> > #10 <http://0.9.8.2/lib/libssh.so.4#10> 0x000000000043547a in >> Hypertable::SshSocketHandler::handle(int, int) () >> > #11 0x0000000000484b9a in >> Hypertable::IOHandlerRaw::handle_event(epoll_event*, long) () >> > #12 0x0000000000492ac4 in >> Hypertable::ReactorRunner::operator()() () >> > #13 0x00007f66010f8ce3 in thread_proxy () from >> /opt/hypertable/doug/0.9.8.2/lib/libboost_thread.so.1.54.0 >> > #14 <http://0.9.8.2/lib/libboost_thread.so.1.54.0#14> >> 0x0000003ee42077f1 in start_thread () from /lib64/libpthread.so.0 >> > #15 0x0000003ee3ae5ccd in clone () from /lib64/libc.so.6 >> > >> > I did a little digging around and came across a ticket filed >> > against sssd <https://fedorahosted.org/sssd/ticket/640> which >> > I believe is the source of the problem. It appears that >> > getpwuid_r() is not thread safe under certain circumstances. >> > >> > From what I can tell, ssh_connect() will use ~/.ssh as the ssh >> > directory if one is not explicitly supplied. It's during the >> > expansion of the ~ character that getpwuid_r() gets called. >> > The workaround is to explicitly set the ssh directory using a >> > path that does not include the ~ character, for example: >> > >> > char *home = getenv("HOME"); >> > if (home == nullptr) >> > error("Environment variable HOME is not set"); >> > string ssh_dir(home); >> > ssh_dir.append("/.ssh"); >> > ssh_options_set(m_ssh_session, SSH_OPTIONS_SSH_DIR, >> > ssh_dir.c_str()); >> > >> > Attached is a patch to libssh that eliminates the ~ expansion >> > for the default case (~/.ssh). In my test environment, the >> > problem is very intermittent and I don't have a reproducible >> > test case, so I'm not 100% sure this solution solves the >> > problem. However, given the evidence, I think it's a safe bet. >> > >> > - Doug >> > >> > -- >> > Doug Judd >> > www.hypertable.com <http://www.hypertable.com> >> > >> > >> > >> > >> > -- >> > Doug Judd >> > CEO, Hypertable Inc. >> > >> > >> > >> > >> > -- >> > Doug Judd >> > CEO, Hypertable Inc. >> >> >> >> > > > -- > Doug Judd > CEO, Hypertable Inc. > -- Doug Judd CEO, Hypertable Inc.
| Re: Infinite loop with concurrent ssh_connect() on CentOS 6 | Aris Adamantiadis <aris@xxxxxxxxxxxx> |
| Infinite loop with concurrent ssh_connect() on CentOS 6 | Doug Judd <doug@xxxxxxxxxxxxxx> |
| Re: Infinite loop with concurrent ssh_connect() on CentOS 6 | Doug Judd <doug@xxxxxxxxxxxxxx> |
| Re: Infinite loop with concurrent ssh_connect() on CentOS 6 | Doug Judd <doug@xxxxxxxxxxxxxx> |
| Re: Infinite loop with concurrent ssh_connect() on CentOS 6 | Aris Adamantiadis <aris@xxxxxxxxxxxx> |
| Re: Infinite loop with concurrent ssh_connect() on CentOS 6 | Doug Judd <doug@xxxxxxxxxxxxxx> |