f9be7b4672
The semaphore has detection and protection against regular resource
leaks, where some resources go unaccounted for and are not released by
the time the semaphore is destroyed. There is no detection or protection
against negative leaks: where resources are "made up" of thin air. This
kind of leaks looks benign at first sight, a few extra resources won't
hurt anyone so long as this is a small amount. But turns out that even a
single extra count resource can defeat a very important anti-deadlock
protection in can_admit_read(): the special case which admits a new
permit regardless of memory resources, when all original count resources
all available. This check uses ==, so if resource > original, the
protection is defeated indefinitely. Instead of just changing == to >=,
we add detection of such negative leaks to signal(), via
on_internal_error_noexcept().
At this time I still don't now how this negative leak happens (the code
doesn't confess), with this detection, hopefully we'll get a clue from
tests or the field. Note that on_internal_error_noexcept() will not
generate a coredump, unless ScyllaDB is explicitely configured to do so.
In production, it will just generate an error log with a backtrace.
The detection also clams the _resources to _initial_resources, to
prevent any damage from the negativae leak.
I just noticed that there is no unit test for the deadlock protection
described above, so one is added in this PR, even if only loosely
related to the rest of the patch.
Fixes: SCYLLADB-163
Closes scylladb/scylladb#27764
(cherry picked from commit e4da0afb8d)
Closes scylladb/scylladb#28000
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++ cqlpy - 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.