Hello everyone:

I'm using openstack mitaka and ceph-jewel-10.2.6 to do snapshot actions. And sometimes it occurs below deadlock condition.

ps -ef | grep cinder-volume
gdb -q python-dbg -p xx


I found 3 frames are racing the lock:

Thread 1 (Thread 0x7ffab0fac740 (LWP 1029)):
#0  0x00007ffab07bf6d5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1  0x00007ffa90c936d0 in Wait (mutex=..., this=0x7ffd91027aa0) at ./common/Cond.h:56
#2  C_SaferCond::wait (this=this@entry=0x7ffd91027a40) at ./common/Cond.h:202
#3  0x00007ffa90cbd7fc in librbd::ImageState<librbd::ImageCtx>::refresh_if_required (this=0x3fb2fb0) at librbd/ImageState.cc:354
#4  0x00007ffa90ce3c10 in librbd::list_children_info (ictx=ictx@entry=0x5257530, parent_spec=..., image_info=std::map with 0 elements) at librbd/internal.cc:926
#5  0x00007ffa90ce5614 in librbd::list_children (ictx=ictx@entry=0x5257530, names=std::set with 0 elements) at librbd/internal.cc:892
#6  0x00007ffa90c79e93 in rbd_list_children (image=0x5257530, pools=pools@entry=0x584fbb0 "hJ\n\260\372\177", pools_len=pools_len@entry=0x7ffd91028118, 
    images=images@entry=0x55f9640 "\250K\n\260\372\177", images_len=images_len@entry=0x7ffd91028120) at librbd/librbd.cc:2423
#7  0x00007ffa9a5a3620 in __pyx_pf_3rbd_5Image_76list_children (__pyx_v_self=0x59110a8) at rbd.c:15450
#8  __pyx_pw_3rbd_5Image_77list_children (__pyx_v_self=0x59110a8, unused=<optimized out>) at rbd.c:15329
#9  0x00007ffab0ab487c in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#10 0x00007ffab0ab6e3d in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0
#11 0x00007ffab0ab433c in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#12 0x00007ffab0ab6e3d in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0
#13 0x00007ffab0ab433c in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#14 0x00007ffab0ab6e3d in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0
#15 0x00007ffab0ab433c in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#16 0x00007ffab0ab6e3d in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0 
....

Thread 12 (Thread 0x7ffa84ac4700 (LWP 1479895)):
#0  0x00007ffab07bf03e in pthread_rwlock_wrlock () from /lib64/libpthread.so.0
#1  0x00007ffa90cc32dc in RWLock::get_write (this=0x52577e0, lockdep=<optimized out>) at ./common/RWLock.h:123
#2  0x00007ffa90d4e7b3 in WLocker (lock=..., this=<synthetic pointer>) at ./common/RWLock.h:183
#3  librbd::image::RefreshRequest<librbd::ImageCtx>::apply (this=this@entry=0x55f9850) at librbd/image/RefreshRequest.cc:860
#4  0x00007ffa90d4f778 in librbd::image::RefreshRequest<librbd::ImageCtx>::handle_v2_apply (this=0x55f9850, result=result@entry=0x7ffa84ac3b2c)
    at librbd/image/RefreshRequest.cc:655
#5  0x00007ffa90d4f92b in librbd::util::detail::C_StateCallbackAdapter<librbd::image::RefreshRequest<librbd::ImageCtx>, &librbd::image::RefreshRequest<librbd::Ima
geCtx>::handle_v2_apply, true>::complete (this=0x7ff9e4002f50, r=0) at ./librbd/Utils.h:66#6  0x00007ffa90cb7644 in ContextWQ::process (this=0x3fd9bf0, ctx=0x7ff9e4002f50) at ./common/WorkQueue.h:608
#7  0x00007ffa90eae54e in ThreadPool::worker (this=0x5180a60, wt=0x56c5430) at common/WorkQueue.cc:128
#8  0x00007ffa90eaf420 in ThreadPool::WorkThread::entry (this=<optimized out>) at common/WorkQueue.h:445
#9  0x00007ffab07bbdc5 in start_thread () from /lib64/libpthread.so.0
#10 0x00007ffaafde176d in clone () from /lib64/libc.so.6


Thread 13 (Thread 0x7ffa852c5700 (LWP 1479894)):
#0  0x00007ffab07bee24 in pthread_rwlock_rdlock () from /lib64/libpthread.so.0
#1  0x00007ffa90c89d2f in RWLock::get_read (this=0x52576c8) at ./common/RWLock.h:100
#2  0x00007ffa90cce5d4 in RLocker (lock=..., this=<synthetic pointer>) at ./common/RWLock.h:161
#3  librbd::ImageWatcher<librbd::ImageCtx>::handle_payload (this=this@entry=0x7ff9e4001d10, payload=..., ack_ctx=ack_ctx@entry=0x7ff9e4001690)
    at librbd/ImageWatcher.cc:673
#4  0x00007ffa90ccee3c in operator()<librbd::watch_notify::ReleasedLockPayload> (payload=..., this=<optimized out>) at ./librbd/ImageWatcher.h:218
#5  internal_visit<librbd::watch_notify::ReleasedLockPayload const> (operand=..., this=<synthetic pointer>) at /usr/include/boost/variant/variant.hpp:1017
#6  visitation_impl_invoke_impl<boost::detail::variant::invoke_visitor<librbd::ImageWatcher<librbd::ImageCtx>::HandlePayloadVisitor const>, void const*, librbd::w
atch_notify::ReleasedLockPayload> (storage=0x7ffa852c4838, visitor=<synthetic pointer>) at /usr/include/boost/variant/detail/visitation_impl.hpp:130#7  visitation_impl_invoke<boost::detail::variant::invoke_visitor<librbd::ImageWatcher<librbd::ImageCtx>::HandlePayloadVisitor const>, void const*, librbd::watch_
notify::ReleasedLockPayload, boost::variant<librbd::watch_notify::AcquiredLockPayload, librbd::watch_notify::ReleasedLockPayload, librbd::watch_notify::RequestLockPayload, librbd::watch_notify::HeaderUpdatePayload, librbd::watch_notify::AsyncProgressPayload, librbd::watch_notify::AsyncCompletePayload, librbd::watch_notify::FlattenPayload, librbd::watch_notify::ResizePayload, librbd::watch_notify::SnapCreatePayload, librbd::watch_notify::SnapRemovePayload, librbd::watch_notify::SnapRenamePayload, librbd::watch_notify::SnapProtectPayload, librbd::watch_notify::SnapUnprotectPayload, librbd::watch_notify::RebuildObjectMapPayload, librbd::watch_notify::RenamePayload, librbd::watch_notify::UnknownPayload>::has_fallback_type_> (internal_which=<optimized out>, t=0x0, storage=0x7ffa852c4838,     visitor=<synthetic pointer>) at /usr/include/boost/variant/detail/visitation_impl.hpp:173
#8  visitation_impl<mpl_::int_<0>, boost::detail::variant::visitation_impl_step<boost::mpl::l_iter<boost::mpl::l_item<mpl_::long_<16l>, librbd::watch_notify::Acqu
iredLockPayload, boost::mpl::l_item<mpl_::long_<15l>, librbd::watch_notify::ReleasedLockPayload, boost::mpl::l_item<mpl_::long_<14l>, librbd::watch_notify::RequestLockPayload, boost::mpl::l_item<mpl_::long_<13l>, librbd::watch_notify::HeaderUpdatePayload, boost::mpl::l_item<mpl_::long_<12l>, librbd::watch_notify::AsyncProgressPayload, boost::mpl::l_item<mpl_::long_<11l>, librbd::watch_notify::AsyncCompletePayload, boost::mpl::l_item<mpl_::long_<10l>, librbd::watch_notify::FlattenPayload, boost::mpl::l_item<mpl_::long_<9l>, librbd::watch_notify::ResizePayload, boost::mpl::l_item<mpl_::long_<8l>, librbd::watch_notify::SnapCreatePayload, boost::mpl::l_item<mpl_::long_<7l>, librbd::watch_notify::SnapRemovePayload, boost::mpl::l_item<mpl_::long_<6l>, librbd::watch_notify::SnapRenamePayload, boost::mpl::l_item<mpl_::long_<5l>, librbd::watch_notify::SnapProtectPayload, boost::mpl::l_item<mpl_::long_<4l>, librbd::watch_notify::SnapUnprotectPayload, boost::mpl::l_item<mpl_::long_<3l>, librbd::watch_notify::RebuildObjectMapPayload, boost::mpl::l_item<mpl_::long_<2l>, librbd::watch_notify::RenamePayload, boost::mpl::l_item<mpl_::long_<1l>, librbd::watch_notify::UnknownPayload, boost::mpl::l_end> > > > > > > > > > > > > > > > >, boost::mpl::l_iter<boost::mpl::l_end> >, boost::detail::variant::invoke_visitor<librbd::ImageWatcher<librbd::ImageCtx>::HandlePayloadVisitor const>, void const*, boost::variant<librbd::watch_notify::AcquiredLockPayload, librbd::watch_notify::ReleasedLockPayload, librbd::watch_notify::RequestLockPayload, librbd::watch_notify::HeaderUpdatePayload, librbd::watch_notify::AsyncProgressPayload, librbd::watch_notify::AsyncCompletePayload, librbd::watch_notify::FlattenPayload, librbd::watch_notify::ResizePayload, librbd::watch_notify::SnapCreatePayload, librbd::watch_notify::SnapRemovePayload, librbd::watch_notify::SnapRenamePayload, librbd::watch_notify::SnapProtectPayload, librbd::watch_notify::SnapUnprotectPayload, librbd::watch_notify::RebuildObjectMapPayload, librbd::watch_notify::RenamePayload, librbd::watch_notify::UnknownPayload>::has_fallback_type_> (no_backup_flag=..., storage=0x7ffa852c4838, visitor=<synthetic pointer>, logical_which=<optimized out>, internal_which=<optimized out>)    at /usr/include/boost/variant/detail/visitation_impl.hpp:256
#9  internal_apply_visitor_impl<boost::detail::variant::invoke_visitor<librbd::ImageWatcher<librbd::ImageCtx>::HandlePayloadVisitor const>, void const*> (
    storage=0x7ffa852c4838, visitor=<synthetic pointer>, logical_which=<optimized out>, internal_which=<optimized out>)
    at /usr/include/boost/variant/variant.hpp:2326
#10 internal_apply_visitor<boost::detail::variant::invoke_visitor<librbd::ImageWatcher<librbd::ImageCtx>::HandlePayloadVisitor const> > (
    visitor=<synthetic pointer>, this=0x7ffa852c4830) at /usr/include/boost/variant/variant.hpp:2348
#11 apply_visitor<librbd::ImageWatcher<librbd::ImageCtx>::HandlePayloadVisitor const> (visitor=..., this=0x7ffa852c4830)
    at /usr/include/boost/variant/variant.hpp:2370
#12 apply_visitor<librbd::ImageWatcher<librbd::ImageCtx>::HandlePayloadVisitor, boost::variant<librbd::watch_notify::AcquiredLockPayload, librbd::watch_notify::Re
leasedLockPayload, librbd::watch_notify::RequestLockPayload, librbd::watch_notify::HeaderUpdatePayload, librbd::watch_notify::AsyncProgressPayload, librbd::watch_notify::AsyncCompletePayload, librbd::watch_notify::FlattenPayload, librbd::watch_notify::ResizePayload, librbd::watch_notify::SnapCreatePayload, librbd::watch_notify::SnapRemovePayload, librbd::watch_notify::SnapRenamePayload, librbd::watch_notify::SnapProtectPayload, librbd::watch_notify::SnapUnprotectPayload, librbd::watch_notify::RebuildObjectMapPayload, librbd::watch_notify::RenamePayload, librbd::watch_notify::UnknownPayload> const> (visitable=..., visitor=...)    at /usr/include/boost/variant/detail/apply_visitor_unary.hpp:76
#13 librbd::ImageWatcher<librbd::ImageCtx>::process_payload (this=this@entry=0x7ff9e4001d10, notify_id=notify_id@entry=1554778161239, 
    handle=handle@entry=140711248795552, payload=..., r=r@entry=0) at librbd/ImageWatcher.cc:974
#14 0x00007ffa90ccf007 in librbd::ImageWatcher<librbd::ImageCtx>::handle_notify (this=0x7ff9e4001d10, notify_id=1554778161239, handle=140711248795552, bl=...)
    at librbd/ImageWatcher.cc:1002
#15 0x00007ffa9d4581b5 in ?? () from /lib64/librados.so.2
#16 0x00007ffa9d4687cc in ?? () from /lib64/librados.so.2
#17 0x00007ffa9d4280c9 in ?? () from /lib64/librados.so.2
#18 0x00007ffa9d515546 in ?? () from /lib64/librados.so.2
#19 0x00007ffab07bbdc5 in start_thread () from /lib64/libpthread.so.0
#20 0x00007ffaafde176d in clone () from /lib64/libc.so.6


I found this:
librbd: possible deadlock with flush if refresh in-progress
https://github.com/ceph/ceph/commit/547e867628975c7144590e9332aa62b0ef82a433#diff-7a45ddfe5905a26e5abed55fe6a17b1d

but i am not sure if this bugfix is for my contiditon.

Thancks a lot if anyone can give advise, ^ _ ^