librbd/cache/pwl: fix memory leak in SyncPoint persist context cleanup

Previously, SyncPoint allocated two C_Gather instances tracked by raw
pointers but failed to properly clean them up when only a single sync
point existed, causing memory leaks detected by AddressSanitizer.

This change fixes the leak by modifying AbstractWriteLog::shut_down()
to check for prior sync points in the chain. When the current sync point
is the only one present, we now activate the m_prior_log_entries_persisted
context to ensure:

- The onfinish callback executes and releases the captured strong
  reference to the enclosing SyncPoint
- The parent m_sync_point_persist context completes and gets properly
  released

This ensures all allocated contexts are cleaned up correctly during
shutdown, eliminating the memory leak.

The ASan report:

```
Indirect leak of 2064 byte(s) in 1 object(s) allocated from:
    #0 0x56440919ae2d in operator new(unsigned long) (/home/jenkins-build/build/workspace/ceph-pull-requests/build/bin/unittest_librbd+0x2f3de2d) (BuildId: 6a04677c6ee5235f1a41815df807f97c5b96d4cd)
    #1 0x56440bd67751 in __gnu_cxx::new_allocator<Context*>::allocate(unsigned long, void const*) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/ext/new_allocator.h:127:27
    #2 0x56440bd676e0 in std::allocator<Context*>::allocate(unsigned long) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/allocator.h:185:32
    #3 0x56440bd676e0 in std::allocator_traits<std::allocator<Context*>>::allocate(std::allocator<Context*>&, unsigned long) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/alloc_traits.h:464:20
    #4 0x56440bd6730b in std::_Vector_base<Context*, std::allocator<Context*>>::_M_allocate(unsigned long) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_vector.h:346:20
    #5 0x7fd33e00e8d1 in std::vector<Context*, std::allocator<Context*>>::reserve(unsigned long) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/vector.tcc:78:22
    #6 0x7fd33e00c51c in librbd::cache::pwl::SyncPoint::SyncPoint(unsigned long, ceph::common::CephContext*) /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/SyncPoint.cc:20:27
    #7 0x56440bd65f26 in decltype(::new((void*)(0)) librbd::cache::pwl::SyncPoint(std::declval<unsigned long&>(), std::declval<ceph::common::CephContext*&>())) std::construct_at<librbd::cache::pwl::SyncPoint, unsigned long&, ceph::common::CephContext*&>(librbd::cache::pwl::SyncPoint*, unsigned long&, ceph::common::CephContext*&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_construct.h:97:39
    #8 0x56440bd65b98 in void std::allocator_traits<std::allocator<librbd::cache::pwl::SyncPoint>>::construct<librbd::cache::pwl::SyncPoint, unsigned long&, ceph::common::CephContext*&>(std::allocator<librbd::cache::pwl::SyncPoint>&, librbd::cache::pwl::SyncPoint*, unsigned long&, ceph::common::CephContext*&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/alloc_traits.h:518:4
    #9 0x56440bd657d3 in std::_Sp_counted_ptr_inplace<librbd::cache::pwl::SyncPoint, std::allocator<librbd::cache::pwl::SyncPoint>, (__gnu_cxx::_Lock_policy)2>::_Sp_counted_ptr_inplace<unsigned long&, ceph::common::CephContext*&>(std::allocator<librbd::cache::pwl::SyncPoint>, unsigned long&, ceph::common::CephContext*&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/shared_ptr_base.h:519:4
    #10 0x56440bd65371 in std::__shared_count<(__gnu_cxx::_Lock_policy)2>::__shared_count<librbd::cache::pwl::SyncPoint, std::allocator<librbd::cache::pwl::SyncPoint>, unsigned long&, ceph::common::CephContext*&>(librbd::cache::pwl::SyncPoint*&, std::_Sp_alloc_shared_tag<std::allocator<librbd::cache::pwl::SyncPoint>>, unsigned long&, ceph::common::CephContext*&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/shared_ptr_base.h:651:6
    #11 0x56440bd65163 in std::__shared_ptr<librbd::cache::pwl::SyncPoint, (__gnu_cxx::_Lock_policy)2>::__shared_ptr<std::allocator<librbd::cache::pwl::SyncPoint>, unsigned long&, ceph::common::CephContext*&>(std::_Sp_alloc_shared_tag<std::allocator<librbd::cache::pwl::SyncPoint>>, unsigned long&, ceph::common::CephContext*&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/shared_ptr_base.h:1342:14
    #12 0x56440bd650e6 in std::shared_ptr<librbd::cache::pwl::SyncPoint>::shared_ptr<std::allocator<librbd::cache::pwl::SyncPoint>, unsigned long&, ceph::common::CephContext*&>(std::_Sp_alloc_shared_tag<std::allocator<librbd::cache::pwl::SyncPoint>>, unsigned long&, ceph::common::CephContext*&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/shared_ptr.h:409:4
    #13 0x56440bd65057 in std::shared_ptr<librbd::cache::pwl::SyncPoint> std::allocate_shared<librbd::cache::pwl::SyncPoint, std::allocator<librbd::cache::pwl::SyncPoint>, unsigned long&, ceph::common::CephContext*&>(std::allocator<librbd::cache::pwl::SyncPoint> const&, unsigned long&, ceph::common::CephContext*&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/shared_ptr.h:862:14
    #14 0x56440bca97e7 in std::shared_ptr<librbd::cache::pwl::SyncPoint> std::make_shared<librbd::cache::pwl::SyncPoint, unsigned long&, ceph::common::CephContext*&>(unsigned long&, ceph::common::CephContext*&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/shared_ptr.h:878:14
    #15 0x56440bd443c8 in librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>::new_sync_point(librbd::cache::pwl::DeferredContexts&) /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/AbstractWriteLog.cc:1905:20
    #16 0x56440bd42e4c in librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>::flush_new_sync_point(librbd::cache::pwl::C_FlushRequest<librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>>*, librbd::cache::pwl::DeferredContexts&) /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/AbstractWriteLog.cc:1951:3
    #17 0x56440bd9cbf2 in librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>::flush_new_sync_point_if_needed(librbd::cache::pwl::C_FlushRequest<librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>>*, librbd::cache::pwl::DeferredContexts&) /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/AbstractWriteLog.cc:1990:5
    #18 0x56440bd9c636 in librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>::internal_flush(bool, Context*)::'lambda'(librbd::cache::pwl::GuardedRequestFunctionContext&)::operator()(librbd::cache::pwl::GuardedRequestFunctionContext&) const /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/AbstractWriteLog.cc:2152:9
    #19 0x56440bd9b9b4 in boost::detail::function::void_function_obj_invoker<librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>::internal_flush(bool, Context*)::'lambda'(librbd::cache::pwl::GuardedRequestFunctionContext&), void, librbd::cache::pwl::GuardedRequestFunctionContext&>::invoke(boost::detail::function::function_buffer&, librbd::cache::pwl::GuardedRequestFunctionContext&) /opt/ceph/include/boost/function/function_template.hpp:100:11
    #20 0x56440bd29321 in boost::function_n<void, librbd::cache::pwl::GuardedRequestFunctionContext&>::operator()(librbd::cache::pwl::GuardedRequestFunctionContext&) const /opt/ceph/include/boost/function/function_template.hpp:789:14
    #21 0x56440bd28d85 in librbd::cache::pwl::GuardedRequestFunctionContext::finish(int) /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/Request.h:335:5
    #22 0x5644091e0fe0 in Context::complete(int) /home/jenkins-build/build/workspace/ceph-pull-requests/src/include/Context.h:102:5
    #23 0x56440bd9b378 in librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>::detain_guarded_request(librbd::cache::pwl::C_BlockIORequest<librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>>*, librbd::cache::pwl::GuardedRequestFunctionContext*, bool) /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/AbstractWriteLog.cc:1202:20
    #24 0x56440bd96c50 in librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>::internal_flush(bool, Context*) /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/AbstractWriteLog.cc:2154:3
    #25 0x56440bd1e4b5 in librbd::cache::pwl::AbstractWriteLog<librbd::MockImageCtx>::shut_down(Context*) /home/jenkins-build/build/workspace/ceph-pull-requests/src/librbd/cache/pwl/AbstractWriteLog.cc:703:3
    #26 0x56440bdb9022 in librbd::cache::pwl::TestMockCacheSSDWriteLog_compare_and_write_compare_matched_Test::TestBody() /home/jenkins-build/build/workspace/ceph-pull-requests/src/test/librbd/cache/pwl/test_mock_SSDWriteLog.cc:403:7
```

Fixes: https://tracker.ceph.com/issues/71335
Signed-off-by: Kefu Chai <tchaikov@gmail.com>
(cherry picked from commit 05fd6f90e6e528c628af7fbb106b73e89d57464c)

diff --git a/src/librbd/cache/pwl/AbstractWriteLog.cc b/src/librbd/cache/pwl/AbstractWriteLog.cc
index b6af9b2ec2d279f41a13bf901cbb65464117c16a..9b188df917f201c2543194a98a667527f19e06fd 100644 (file)
--- a/src/librbd/cache/pwl/AbstractWriteLog.cc
+++ b/src/librbd/cache/pwl/AbstractWriteLog.cc
@@ -657,6 +657,20 @@ void AbstractWriteLog<I>::shut_down(Context *on_finish) {
       periodic_stats();
 
       std::unique_lock locker(m_lock);
+
+      ceph_assert(m_current_sync_point);
+      if (!m_current_sync_point->earlier_sync_point) {
+        // This is the only sync point, hence no need to wait for the persistence
+        // of prior sync points.
+        m_current_sync_point->prior_persisted_gather_activate();
+        // we don't create a new sync point, if there are no writes in current sync point's
+        // log entry.
+        ceph_assert(m_current_sync_point->log_entry->writes == 0);
+        // In that case, we shold not wait for the log entry's persistence of current
+        // sync point, which is otherwise waited until we flush its prior sync point.
+        m_current_sync_point->persist_gather_activate();
+      }
+
       check_image_cache_state_clean();
       m_wake_up_enabled = false;
       m_log_entries.clear();