MySQL Bugs: #116580: Forever hang after connection drop

Bug #116580	Forever hang after connection drop
Submitted:	7 Nov 9:19	Modified:	15 Nov 11:01
Reporter:	Val Doroshchuk	Email Updates:
Status:	Verified	Impact on me:	None
Category:	Connector / C++	Severity:	S3 (Non-critical)
Version:	8.0	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
There might be forever hang after the connection is dropped by MySQL.
The hang happens for SSL ENABLED and DISABLED modes:

for SSLMode::DISABLED:
#0  0x00007aa463118bcf in __GI___poll (fds=0x7fff82106030, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007aa463d3fdff in cdk::foundation::connection::detail::poll_one (socket=3, mode=cdk::foundation::connection::detail::POLL_MODE_READ, wait=true, timeout_usec=0) at ./cdk/foundation/socket_detail.cc:881
#2  0x00007aa463d3fff0 in cdk::foundation::connection::detail::recv_some (socket=3, buffer=0x55a075bdfdb0 "\n\002\340Y\nA96c5f63935aff2e9887df4e3307aa342ce43fe8a750000daac86c933eee2ba99", buffer_size=5, wait=true) at ./cdk/foundation/socket_detail.cc:950
#3  0x00007aa463d3fee6 in cdk::foundation::connection::detail::recv (socket=3, buffer=0x55a075bdfdb0 "\n\002\340Y\nA96c5f63935aff2e9887df4e3307aa342ce43fe8a750000daac86c933eee2ba99", buffer_size=5) at ./cdk/foundation/socket_detail.cc:920
#4  0x00007aa463d3b2f0 in cdk::foundation::connection::Socket_base::Read_op::do_wait (this=0x55a075b91530) at ./cdk/foundation/connection_tcpip.cc:282

for SSLMode::ENABLED:
#9  0x0000736cbc6a7cb7 in SSL_read () from /lib/x86_64-linux-gnu/libssl.so.3
#10 0x0000736cbcd43d77 in cdk::foundation::connection::TLS::Read_op::common_read (this=0x63e4c17d71d0) at ./cdk/foundation/connection_openssl.cc:931
#11 0x0000736cbcd43c54 in cdk::foundation::connection::TLS::Read_op::do_cont (this=0x63e4c17d71d0) at ./cdk/foundation/connection_openssl.cc:909

Similar to https://bugs.mysql.com/bug.php?id=92325

How to repeat:
The test case similar for https://bugs.mysql.com/bug.php?id=116569 but need to increase time of packets loss.

Steps:
1. Create big enough table
2. Set mysqlx_write_timeout to very low value, after MySQL will close the connection. 
3. Execute SELECT query using mysqlx::Session
4. During executing, simulate the drop of all packets during long period.
5. You get the forever hang. If the packet loss is not so long. It would lead to crash as https://bugs.mysql.com/bug.php?id=116569
The test case would be the same, unless time of the packet loss.

$ sudo XPLUGIN_SHOULD_HANG=1 XPLUGIN_PORT=5445  ./run_unit_tests --gtest_filter=Sess.connection_drop

TEST_F(Sess, connection_drop)
{
  SKIP_IF_NO_XPLUGIN;

  try {
    get_sess().dropSchema("connection_drop");
  } catch (...) {}

  EXPECT_TRUE(get_sess().createSchema("connection_drop").existsInDatabase());

  std::string sql;
  sql = R"sql(
    CREATE TABLE connection_drop.t(
      id INT PRIMARY KEY AUTO_INCREMENT,
      hash CHAR(64)
    ))sql";
  get_sess().sql(sql).execute();
  // This closes connection after 1 second of inactivity
  get_sess().sql("SET SESSION mysqlx_write_timeout = 1").execute();
  get_sess().sql("SET SESSION cte_max_recursion_depth = 2000000").execute();
  // Generate enough data to spend some time in executing the query
  sql = R"sql(
    INSERT INTO connection_drop.t(hash)
    WITH RECURSIVE cte (n) AS
    (
      SELECT 1
      UNION ALL
      SELECT n + 1 FROM cte WHERE n < 2000000
    )
    SELECT SHA2(n, 256) FROM cte
    )sql";
  get_sess().sql(sql).execute();

  // Requires long delay
  bool shouldHang = getenv("XPLUGIN_SHOULD_HANG") != nullptr;
  std::thread t([&] {
    // Force 100% packet loss for XPLUGIN_PORT
    system("tc qdisc add dev lo root handle 1: prio priomap 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0");
    system("tc qdisc add dev lo parent 1:2 handle 20: netem loss 100%");
    system(std::string("tc filter add dev lo parent 1:0 protocol ip u32 match ip sport " + std::to_string(get_port()) + " 0xffff flowid 1:2").c_str());
    std::chrono::seconds sec(shouldHang ? 60 : 5);
    std::this_thread::sleep_for(sec);
    system("tc qdisc del dev lo root");
    // Crash or hang should be after this
  });

  get_sess().sql("SELECT * FROM connection_drop.t").execute();
  t.join();
  try {
    get_sess().dropSchema("connection_drop");
  } catch (...) {}
}

#0  0x00007aa463118bcf in __GI___poll (fds=0x7fff82106030, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007aa463d3fdff in cdk::foundation::connection::detail::poll_one (socket=3, mode=cdk::foundation::connection::detail::POLL_MODE_READ, wait=true, timeout_usec=0) at ./cdk/foundation/socket_detail.cc:881
#2  0x00007aa463d3fff0 in cdk::foundation::connection::detail::recv_some (socket=3, buffer=0x55a075bdfdb0 "\n\002\340Y\nA96c5f63935aff2e9887df4e3307aa342ce43fe8a750000daac86c933eee2ba99", buffer_size=5, wait=true) at ./cdk/foundation/socket_detail.cc:950
#3  0x00007aa463d3fee6 in cdk::foundation::connection::detail::recv (socket=3, buffer=0x55a075bdfdb0 "\n\002\340Y\nA96c5f63935aff2e9887df4e3307aa342ce43fe8a750000daac86c933eee2ba99", buffer_size=5) at ./cdk/foundation/socket_detail.cc:920
#4  0x00007aa463d3b2f0 in cdk::foundation::connection::Socket_base::Read_op::do_wait (this=0x55a075b91530) at ./cdk/foundation/connection_tcpip.cc:282
#5  0x00007aa463959208 in cdk::foundation::api::Async_op_base::wait (this=0x55a075b91530) at ./cdk/include/mysql/cdk/protocol/../foundation/async.h:78
#6  0x00007aa463a8ac88 in cdk::protocol::mysqlx::Protocol_impl::rd_wait (this=0x55a075b90ba0) at ./cdk/protocol/mysqlx/protocol.cc:595
#7  0x00007aa463a8b1b3 in cdk::protocol::mysqlx::Op_rcv::do_read_msg (this=0x55a075b8c400, async=false) at ./cdk/protocol/mysqlx/protocol.cc:756
#8  0x00007aa463a8b583 in cdk::protocol::mysqlx::Op_rcv::do_wait (this=0x55a075b8c400) at ./cdk/protocol/mysqlx/protocol.cc:903
#9  0x00007aa463959208 in cdk::foundation::api::Async_op_base::wait (this=0x55a075b8c400) at ./cdk/include/mysql/cdk/foundation/async.h:78
#10 0x00007aa463a849eb in cdk::mysqlx::Stmt_op::do_wait (this=0x55a075b8a5a0) at ./cdk/mysqlx/result.cc:236
#11 0x00007aa463959208 in cdk::foundation::api::Async_op_base::wait (this=0x55a075b8a5a0) at ./cdk/include/mysql/cdk/foundation/async.h:78
#12 0x00007aa463a84b78 in cdk::mysqlx::Stmt_op::discard_result (this=0x55a075b8a5a0) at ./cdk/mysqlx/result.cc:277
#13 0x00007aa463a717cf in cdk::mysqlx::Stmt_op::discard (this=0x55a075b8a5a0) at ./cdk/include/mysql/cdk/mysqlx/result.h:633
#14 0x00007aa463a7655b in cdk::mysqlx::Expectation<cdk::mysqlx::Query_stmt, (cdk::protocol::mysqlx::api::Protocol_fields::value)4>::~Expectation (this=0x55a075b8a5a0, __in_chrg=<optimized out>) at ./cdk/mysqlx/stmt.h:130
#15 0x00007aa463a72df7 in cdk::mysqlx::Prepared<cdk::mysqlx::Query_stmt>::~Prepared (this=0x55a075b8a5a0, __in_chrg=<optimized out>) at ./cdk/mysqlx/stmt.h:403
#16 0x00007aa463a7e191 in cdk::mysqlx::Cmd_StmtExecute::~Cmd_StmtExecute (this=0x55a075b8a5a0, __in_chrg=<optimized out>) at ./cdk/mysqlx/stmt.h:604
#17 0x00007aa463a7e1ee in cdk::mysqlx::Cmd_StmtExecute::~Cmd_StmtExecute (this=0x55a075b8a5a0, __in_chrg=<optimized out>) at ./cdk/mysqlx/stmt.h:604
#18 0x00007aa46398fe4c in std::_Sp_counted_ptr<cdk::mysqlx::Stmt_op*, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=0x55a075b91090) at /usr/include/c++/10/bits/shared_ptr_base.h:380
#19 0x000055a075043831 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x55a075b91090) at /usr/include/c++/10/bits/shared_ptr_base.h:158
#20 0x000055a075035221 in std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=0x55a075bde0c8, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr_base.h:736
#21 0x00007aa46395a778 in std::__shared_ptr<cdk::mysqlx::Stmt_op, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=0x55a075bde0c0, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr_base.h:1188
#22 0x00007aa46395a798 in std::shared_ptr<cdk::mysqlx::Stmt_op>::~shared_ptr (this=0x55a075bde0c0, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr.h:121
#23 0x00007aa4639755cb in cdk::Reply::~Reply (this=0x55a075bde0b0, __in_chrg=<optimized out>) at ./cdk/include/mysql/cdk/reply.h:44
#24 0x00007aa463975600 in cdk::Reply::~Reply (this=0x55a075bde0b0, __in_chrg=<optimized out>) at ./cdk/include/mysql/cdk/reply.h:44
#25 0x00007aa463a42d34 in mysqlx::abi2::r0::common::Result_impl::~Result_impl (this=0x55a075b74ef0, __in_chrg=<optimized out>) at ./common/result.cc:193
#26 0x00007aa463a42dda in mysqlx::abi2::r0::common::Result_impl::~Result_impl (this=0x55a075b74ef0, __in_chrg=<optimized out>) at ./common/result.cc:194
#27 0x00007aa4639f17ee in mysqlx::abi2::r0::internal::Result_detail::~Result_detail (this=0x7fff82106770, __in_chrg=<optimized out>) at ./devapi/result.cc:495
#28 0x000055a07502a6f2 in mysqlx::abi2::r0::internal::Row_result_detail<mysqlx::abi2::r0::Columns>::~Row_result_detail (this=0x7fff82106770, __in_chrg=<optimized out>) at ./include/mysqlx/devapi/detail/result.h:314
#29 0x000055a07502a750 in mysqlx::abi2::r0::internal::Result_common<mysqlx::abi2::r0::internal::Row_result_detail<mysqlx::abi2::r0::Columns> >::~Result_common (this=0x7fff82106770, __in_chrg=<optimized out>) at ./include/mysqlx/devapi/result.h:71
#30 0x000055a07502ade6 in mysqlx::abi2::r0::RowResult::~RowResult (this=0x7fff82106770, __in_chrg=<optimized out>) at ./include/mysqlx/devapi/result.h:585
#31 0x000055a07512a340 in mysqlx::abi2::r0::SqlResult::~SqlResult (this=0x7fff82106770, __in_chrg=<optimized out>) at ./include/mysqlx/devapi/result.h:730
#32 0x000055a075236564 in Sess_connection_drop_Test::TestBody (this=0x55a075b77150) at ./devapi/tests/session-t.cc:4380
#33 0x000055a0753080bf in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) ()
#34 0x000055a075300be3 in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) ()
#35 0x000055a0752dc3f0 in testing::Test::Run() ()
#36 0x000055a0752dce34 in testing::TestInfo::Run() ()
#37 0x000055a0752dd7c4 in testing::TestSuite::Run() ()
#38 0x000055a0752edafc in testing::internal::UnitTestImpl::RunAllTests() ()
#39 0x000055a07530964c in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) ()
#40 0x000055a075301e85 in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) ()
#41 0x000055a0752ec111 in testing::UnitTest::Run() ()
#42 0x000055a074f603e9 in RUN_ALL_TESTS () at /opt/googletest-1.15.2/include/gtest/gtest.h:2334
#43 0x000055a074f60309 in main (argc=1, argv=0x7fff82107028) at ./build/tests_main.cc:66

Thread 1 (Thread 0x736cbcf5d5c0 (LWP 61730) "run_unit_tests"):
#0  __GI___libc_read (nbytes=541, buf=0x63e4c17cfb4c, fd=3) at ../sysdeps/unix/sysv/linux/read.c:26
#1  __GI___libc_read (fd=3, buf=0x63e4c17cfb4c, nbytes=541) at ../sysdeps/unix/sysv/linux/read.c:24
#2  0x0000736cbbae1e3d in ?? () from /lib/x86_64-linux-gnu/libcrypto.so.3
#3  0x0000736cbbad234b in ?? () from /lib/x86_64-linux-gnu/libcrypto.so.3
#4  0x0000736cbbad5345 in ?? () from /lib/x86_64-linux-gnu/libcrypto.so.3
#5  0x0000736cbbad54c7 in BIO_read () from /lib/x86_64-linux-gnu/libcrypto.so.3
#6  0x0000736cbc6c53cc in ?? () from /lib/x86_64-linux-gnu/libssl.so.3
#7  0x0000736cbc6c7332 in ?? () from /lib/x86_64-linux-gnu/libssl.so.3
#8  0x0000736cbc6a13fc in ?? () from /lib/x86_64-linux-gnu/libssl.so.3
#9  0x0000736cbc6a7cb7 in SSL_read () from /lib/x86_64-linux-gnu/libssl.so.3
#10 0x0000736cbcd43d77 in cdk::foundation::connection::TLS::Read_op::common_read (this=0x63e4c17d71d0) at ./cdk/foundation/connection_openssl.cc:931
#11 0x0000736cbcd43c54 in cdk::foundation::connection::TLS::Read_op::do_cont (this=0x63e4c17d71d0) at ./cdk/foundation/connection_openssl.cc:909
#12 0x0000736cbc9591c3 in cdk::foundation::api::Async_op_base::cont (this=0x63e4c17d71d0) at ./cdk/include/mysql/cdk/protocol/../foundation/async.h:72
#13 0x0000736cbca8abbe in cdk::protocol::mysqlx::Protocol_impl::rd_cont (this=0x63e4c1724970) at ./cdk/protocol/mysqlx/protocol.cc:575
#14 0x0000736cbca8ac32 in cdk::protocol::mysqlx::Protocol_impl::rd_wait (this=0x63e4c1724970) at ./cdk/protocol/mysqlx/protocol.cc:591
#15 0x0000736cbca8b1b3 in cdk::protocol::mysqlx::Op_rcv::do_read_msg (this=0x63e4c17d7680, async=false) at ./cdk/protocol/mysqlx/protocol.cc:756
#16 0x0000736cbca8b583 in cdk::protocol::mysqlx::Op_rcv::do_wait (this=0x63e4c17d7680) at ./cdk/protocol/mysqlx/protocol.cc:903
#17 0x0000736cbc959208 in cdk::foundation::api::Async_op_base::wait (this=0x63e4c17d7680) at ./cdk/include/mysql/cdk/foundation/async.h:78
#18 0x0000736cbca849eb in cdk::mysqlx::Stmt_op::do_wait (this=0x63e4c171e5a0) at ./cdk/mysqlx/result.cc:236
#19 0x0000736cbc959208 in cdk::foundation::api::Async_op_base::wait (this=0x63e4c171e5a0) at ./cdk/include/mysql/cdk/foundation/async.h:78
#20 0x0000736cbca84b78 in cdk::mysqlx::Stmt_op::discard_result (this=0x63e4c171e5a0) at ./cdk/mysqlx/result.cc:277
#21 0x0000736cbca717cf in cdk::mysqlx::Stmt_op::discard (this=0x63e4c171e5a0) at ./cdk/include/mysql/cdk/mysqlx/result.h:633
#22 0x0000736cbca7655b in cdk::mysqlx::Expectation<cdk::mysqlx::Query_stmt, (cdk::protocol::mysqlx::api::Protocol_fields::value)4>::~Expectation (this=0x63e4c171e5a0, __in_chrg=<optimized out>) at ./cdk/mysqlx/stmt.h:130
#23 0x0000736cbca72df7 in cdk::mysqlx::Prepared<cdk::mysqlx::Query_stmt>::~Prepared (this=0x63e4c171e5a0, __in_chrg=<optimized out>) at ./cdk/mysqlx/stmt.h:403
#24 0x0000736cbca7e191 in cdk::mysqlx::Cmd_StmtExecute::~Cmd_StmtExecute (this=0x63e4c171e5a0, __in_chrg=<optimized out>) at ./cdk/mysqlx/stmt.h:604
#25 0x0000736cbca7e1ee in cdk::mysqlx::Cmd_StmtExecute::~Cmd_StmtExecute (this=0x63e4c171e5a0, __in_chrg=<optimized out>) at ./cdk/mysqlx/stmt.h:604
#26 0x0000736cbc98fe4c in std::_Sp_counted_ptr<cdk::mysqlx::Stmt_op*, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=0x63e4c17d7240) at /usr/include/c++/10/bits/shared_ptr_base.h:380
#27 0x000063e4c00c3823 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x63e4c17d7240) at /usr/include/c++/10/bits/shared_ptr_base.h:158
#28 0x000063e4c00b521d in std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=0x63e4c171fff8, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr_base.h:736
#29 0x0000736cbc95a778 in std::__shared_ptr<cdk::mysqlx::Stmt_op, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=0x63e4c171fff0, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr_base.h:1188
#30 0x0000736cbc95a798 in std::shared_ptr<cdk::mysqlx::Stmt_op>::~shared_ptr (this=0x63e4c171fff0, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr.h:121
#31 0x0000736cbc9755cb in cdk::Reply::~Reply (this=0x63e4c171ffe0, __in_chrg=<optimized out>) at ./cdk/include/mysql/cdk/reply.h:44
#32 0x0000736cbc975600 in cdk::Reply::~Reply (this=0x63e4c171ffe0, __in_chrg=<optimized out>) at ./cdk/include/mysql/cdk/reply.h:44
#33 0x0000736cbca42d34 in mysqlx::abi2::r0::common::Result_impl::~Result_impl (this=0x63e4c17d8b70, __in_chrg=<optimized out>) at ./common/result.cc:193
#34 0x0000736cbca42dda in mysqlx::abi2::r0::common::Result_impl::~Result_impl (this=0x63e4c17d8b70, __in_chrg=<optimized out>) at ./common/result.cc:194
#35 0x0000736cbc9f17ee in mysqlx::abi2::r0::internal::Result_detail::~Result_detail (this=0x7ffca2ef96b0, __in_chrg=<optimized out>) at ./devapi/result.cc:495
#36 0x000063e4c00aa6f2 in mysqlx::abi2::r0::internal::Row_result_detail<mysqlx::abi2::r0::Columns>::~Row_result_detail (this=0x7ffca2ef96b0, __in_chrg=<optimized out>) at ./include/mysqlx/devapi/detail/result.h:314
#37 0x000063e4c00aa750 in mysqlx::abi2::r0::internal::Result_common<mysqlx::abi2::r0::internal::Row_result_detail<mysqlx::abi2::r0::Columns> >::~Result_common (this=0x7ffca2ef96b0, __in_chrg=<optimized out>) at ./include/mysqlx/devapi/result.h:71
#38 0x000063e4c00aade6 in mysqlx::abi2::r0::RowResult::~RowResult (this=0x7ffca2ef96b0, __in_chrg=<optimized out>) at ./include/mysqlx/devapi/result.h:585
#39 0x000063e4c01a9fda in mysqlx::abi2::r0::SqlResult::~SqlResult (this=0x7ffca2ef96b0, __in_chrg=<optimized out>) at ./include/mysqlx/devapi/result.h:730
#40 0x000063e4c02b61fe in Sess_connection_drop_Test::TestBody (this=0x63e4c170b150) at ./devapi/tests/session-t.cc:4380
#41 0x000063e4c0387ceb in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) ()
#42 0x000063e4c038080f in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) ()
#43 0x000063e4c035c01c in testing::Test::Run() ()
#44 0x000063e4c035ca60 in testing::TestInfo::Run() ()
#45 0x000063e4c035d3f0 in testing::TestSuite::Run() ()
#46 0x000063e4c036d728 in testing::internal::UnitTestImpl::RunAllTests() ()
#47 0x000063e4c0389278 in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) ()
--Type <RET> for more, q to quit, c to continue without paging--
#48 0x000063e4c0381ab1 in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) ()
#49 0x000063e4c036bd3d in testing::UnitTest::Run() ()
#50 0x000063e4bffe03e9 in RUN_ALL_TESTS () at /opt/googletest-1.15.2/include/gtest/gtest.h:2334
#51 0x000063e4bffe0309 in main (argc=1, argv=0x7ffca2ef9f68) at ./build/tests_main.cc:66

Hi Val,

We will analyze this bug together with Bug# 116569 and update both bugs statuses once it is done.

Thank you Mr. Doroshchuk,

This is now a fully verified bug for the version 8.0 and higher.

Posted by developer:
 
There is old bug#92325 which reports similar issue and explains which part of the code could be responsible for that. Since then the code was fixed to remove the issue. Can you see if the issue can be reproduced with the current code (version 9.1.0)?

Thank you, Rafal.

Thank you, Rafal!

> Since then the code was fixed to remove the issue. Can you see if the issue can be reproduced with the current code (version 9.1.0)?

It is reproducible in 9.1.0 and trunk too. By test provided. Idea that MySQL closes the connection after `mysqlx_write_timeout`, and if the mysqlx::Session is throttled for too long, something bad happens and poll() or SSL_read() never wakes up. 

Please look at recv_some():

int select_result = poll_one(socket, POLL_MODE_READ, wait); << timeout_usec is -1 means infinite.

Even if you add the timeout here, f.e.

int select_result = poll_one(socket, POLL_MODE_READ, wait, 100000);

it won't help since you would need to fix also 

void recv(Socket socket, byte *buffer, size_t buffer_size)
{

  while (bytes_received != buffer_size) << it should exit the loop when no bytes received
    bytes_received += recv_some(socket, buffer + bytes_received, buffer_size - bytes_received, true);

Posted by developer:
 
Hmm, you are right -- the problem is in `connection::detail::recv()` function which assumes that a call to `recv_some()` will return a non-zero amount of received bytes (or throw error). But `recv_some()` can also return 0 in some cases... We need to look at this closer. Thanks for good analysis!

Thank you, Rafal ......