Fix GetMergeOperands() heap-use-after-free on flushed memtable

[ajkr]

Fixes #9066.

Prior to the fix in this PR, this PR's unit test reported the following error under ASAN:

==2175705==ERROR: AddressSanitizer: heap-use-after-free on address 0x61f0000012a5 at pc 0x7f0fc36e76ce bp 0x7ffc103e9ca0 sp 0x7ffc103e9450
READ of size 5 at 0x61f0000012a5 thread T0
    #0 0x7f0fc36e76cd in __interceptor_memcpy /home/engshare/third-party2/gcc/9.x/src/gcc-10.x/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:790
    #1 0x7f0fc35a207e in std::char_traits<char>::copy(char*, char const*, unsigned long) /home/engshare/third-party2/libgcc/9.x/src/gcc-9.x/x86_64-facebook-linux/libstdc++-v3/include/bits/char_traits.h:365
    #2 0x7f0fc35a207e in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_S_copy(char*, char const*, unsigned long) /home/engshare/third-party2/libgcc/9.x/src/gcc-9.x/x86_64-facebook-linux/libstdc++-v3/include/bits/basic_string.h:351
    #3 0x7f0fc35a207e in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_replace(unsigned long, unsigned long, char const*, unsigned long) /home/engshare/third-party2/libgcc/9.x/src/gcc-9.x/x86_64-facebook-linux/libstdc++-v3/include/bits/basic_string.tcc:440
    #4 0x8679ca in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::assign(char const*, unsigned long) /mnt/gvfs/third-party2/libgcc/4959b39cfbe5965a37c861c4c327fa7c5c759b87/9.x/platform009/9202ce7/include/c++/9.3.0/bits/basic_string.h:1422
    #5 0x8679ca in rocksdb::PinnableSlice::PinSelf(rocksdb::Slice const&) include/rocksdb/slice.h:171
    #6 0x8679ca in rocksdb::DBImpl::GetImpl(rocksdb::ReadOptions const&, rocksdb::Slice const&, rocksdb::DBImpl::GetImplOptions&) db/db_impl/db_impl.cc:1930
    #7 0x547324 in rocksdb::DBImpl::GetMergeOperands(rocksdb::ReadOptions const&, rocksdb::ColumnFamilyHandle*, rocksdb::Slice const&, rocksdb::PinnableSlice*, rocksdb::GetMergeOperandsOptions*, int*) db/db_impl/db_impl.h:203
    #8 0x547324 in rocksdb::DBMergeOperandTest_FlushedMergeOperandReadAfterFreeBug_Test::TestBody() db/db_merge_operand_test.cc:117
    #9 0x7241da in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3899
    #10 0x7241da in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3935
    #11 0x701a47 in testing::Test::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3973
    #12 0x702040 in testing::Test::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3965
    #13 0x702040 in testing::TestInfo::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4149
    #14 0x7025f7 in testing::TestInfo::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4124
    #15 0x7025f7 in testing::TestCase::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4267
    #16 0x704217 in testing::TestCase::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4253
    #17 0x704217 in testing::internal::UnitTestImpl::RunAllTests() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:6633
    #18 0x72505a in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3899
    #19 0x72505a in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3935
    #20 0x704aa1 in testing::UnitTest::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:6242
    #21 0x4c4aff in RUN_ALL_TESTS() third-party/gtest-1.8.1/fused-src/gtest/gtest.h:22110
    #22 0x4c4aff in main db/db_merge_operand_test.cc:404
    #23 0x7f0fc3108dc4 in __libc_start_main ../csu/libc-start.c:308
    #24 0x5445fd in _start (/data/users/andrewkr/rocksdb/db_merge_operand_test+0x5445fd)

0x61f0000012a5 is located 1061 bytes inside of 3264-byte region [0x61f000000e80,0x61f000001b40)
freed by thread T0 here:
    #0 0x7f0fc375b6af in operator delete(void*, unsigned long) /home/engshare/third-party2/gcc/9.x/src/gcc-10.x/libsanitizer/asan/asan_new_delete.cc:177
    #1 0x743be8 in rocksdb::SuperVersion::~SuperVersion() db/column_family.cc:432
    #2 0x8052aa in rocksdb::DBImpl::CleanupSuperVersion(rocksdb::SuperVersion*) db/db_impl/db_impl.cc:3534
    #3 0x8676c2 in rocksdb::DBImpl::ReturnAndCleanupSuperVersion(rocksdb::ColumnFamilyData*, rocksdb::SuperVersion*) db/db_impl/db_impl.cc:3544
    #4 0x8676c2 in rocksdb::DBImpl::GetImpl(rocksdb::ReadOptions const&, rocksdb::Slice const&, rocksdb::DBImpl::GetImplOptions&) db/db_impl/db_impl.cc:1911
    #5 0x547324 in rocksdb::DBImpl::GetMergeOperands(rocksdb::ReadOptions const&, rocksdb::ColumnFamilyHandle*, rocksdb::Slice const&, rocksdb::PinnableSlice*, rocksdb::GetMergeOperandsOptions*, int*) db/db_impl/db_impl.h:203
    #6 0x547324 in rocksdb::DBMergeOperandTest_FlushedMergeOperandReadAfterFreeBug_Test::TestBody() db/db_merge_operand_test.cc:117
    #7 0x7241da in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3899
    #8 0x7241da in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3935
    #9 0x701a47 in testing::Test::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3973
    #10 0x702040 in testing::Test::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3965
    #11 0x702040 in testing::TestInfo::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4149
    #12 0x7025f7 in testing::TestInfo::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4124
    #13 0x7025f7 in testing::TestCase::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4267
    #14 0x704217 in testing::TestCase::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:4253
    #15 0x704217 in testing::internal::UnitTestImpl::RunAllTests() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:6633
    #16 0x72505a in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3899
    #17 0x72505a in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:3935
    #18 0x704aa1 in testing::UnitTest::Run() third-party/gtest-1.8.1/fused-src/gtest/gtest-all.cc:6242
    #19 0x4c4aff in RUN_ALL_TESTS() third-party/gtest-1.8.1/fused-src/gtest/gtest.h:22110
    #20 0x4c4aff in main db/db_merge_operand_test.cc:404
    #21 0x7f0fc3108dc4 in __libc_start_main ../csu/libc-start.c:308
    #22 0x5445fd in _start (/data/users/andrewkr/rocksdb/db_merge_operand_test+0x5445fd)
...

Test Plan: following the fix in this PR, the new unit test passes

[facebook-github-bot]

@ajkr has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[jay-zhuang]

LGTM.

[ajkr]

Thanks for the review!