dcddb1ff4a
Passing an admitted permit -- i.e. one with count resources on it -- to the multishard reader, will possibly result in a deadlock, because the permit of the multishard reader is destroyed after the permits of its child readers. Therefore its semaphore resources won't be automatically released until children acquire their own resources. This creates a dependency (an edge in the "resource allocation graph"), where the semaphore used by the multishard reader depends on the semaphores used by children. When such dependencies create a cycle, and permits are acquired by different reads in just the right order, a deadlock will happen. Users of the multishard reader have to be aware of this gotcha -- and of course they aren't. This is small wonder, considering that not even the documentation on the multishard reader mentions this problem. To work around this, the user has to call `reader_permit::release_base_resources()` on the permit, before passing it to the multishard reader. On multiple occasions, developers (including the very author of the multishard reader), forgot or didn't know about this and this resulted in deadlocks down the line. This is a design-flaw of the multishard reader, which is addressed in this PR, after which, it is safe to pass admitted or not admitted permits to the multishard reader, it will handle the call to `release_base_resources()` if needed. After fixing the problem in the multishard reader, the existing calls to `release_base_resources()` on permits passed to multishard readers are removed. A test is added which reproduces the problem and ensures we don't regress. Refs: https://github.com/scylladb/scylladb/issues/20885 (partial fix, there is another deadlock in that issue, which this PR doesn't fix) Fixes: https://github.com/scylladb/scylladb/issues/21263 This fixes (indirectly) a regression introduced byd98708013cso it has to be backported to 6.2 (cherry picked from commite1d8cddd09) Refs scylladb/scylladb#21058 Closes scylladb/scylladb#21178 * github.com:scylladb/scylladb: test/boost/mutation_test: add test for multishard permit safety test/lib/reader_lifecycle_policy: add semaphore factory to constructor test/lib/reader_lifecycle_policy: rename factory_function repair/row_level: drop now unneeded release_base_resource() calls readers/multishard: make multishard reader safe to create with admitted permits
Scylla in-source tests.
For details on how to run the tests, see docs/dev/testing.md
Shared C++ utils, libraries are in lib/, for Python - pylib/
alternator - Python tests which connect to a single server and use the DynamoDB API unit, boost, raft - unit tests in C++ cql-pytest - Python tests which connect to a single server and use CQL topology* - tests that set up clusters and add/remove nodes cql - approval tests that use CQL and pre-recorded output rest_api - tests for Scylla REST API Port 9000 scylla-gdb - tests for scylla-gdb.py helper script nodetool - tests for C++ implementation of nodetool
If you can use an existing folder, consider adding your test to it. New folders should be used for new large categories/subsystems, or when the test environment is significantly different from some existing suite, e.g. you plan to start scylladb with different configuration, and you intend to add many tests and would like them to reuse an existing Scylla cluster (clusters can be reused for tests within the same folder).
To add a new folder, create a new directory, and then
copy & edit its suite.ini.