8 Commits (c95d2159c1dd3f269383a9bd830e1c804dba34c8)

Author	SHA1	Message	Date
Michael Paquier	a0a5869a85	Add INJECTION_POINT_CACHED() to run injection points directly from cache ... This new macro is able to perform a direct lookup from the local cache of injection points (refreshed each time a point is loaded or run), without touching the shared memory state of injection points at all. This works in combination with INJECTION_POINT_LOAD(), and it is better than INJECTION_POINT() in a critical section due to the fact that it would avoid all memory allocations should a concurrent detach happen since a LOAD(), as it retrieves a callback from the backend-private memory. The documentation is updated to describe in more details how to use this new macro with a load. Some tests are added to the module injection_points based on a new SQL function that acts as a wrapper of INJECTION_POINT_CACHED(). Based on a suggestion from Heikki Linnakangas. Author: Heikki Linnakangas, Michael Paquier Discussion: https://postgr.es/m/58d588d0-e63f-432f-9181-bed29313dece@iki.fi	1 year ago
Heikki Linnakangas	86db52a506	Use atomics to avoid locking in InjectionPointRun() ... This allows using injection points without having a PGPROC, like early at backend startup, or in the postmaster. The injection points facility is new in v17, so backpatch there. Reviewed-by: Michael Paquier <michael@paquier.xyz> Disussion: https://www.postgresql.org/message-id/4317a7f7-8d24-435e-9e49-29b72a3dc418@iki.fi	1 year ago
Michael Paquier	4b211003ec	Support loading of injection points ... This can be used to load an injection point and prewarm the backend-level cache before running it, to avoid issues if the point cannot be loaded due to restrictions in the code path where it would be run, like a critical section where no memory allocation can happen (load_external_function() can do allocations when expanding a library name). Tests can use a macro called INJECTION_POINT_LOAD() to load an injection point. The test module injection_points gains some tests, and a SQL function able to load an injection point. Based on a request from Andrey Borodin, who has implemented a test for multixacts requiring this facility. Reviewed-by: Andrey Borodin Discussion: https://postgr.es/m/ZkrBE1e2q2wGvsoN@paquier.xyz	1 year ago
Michael Paquier	d85fc4be11	Improve locking around InjectionPointRun() ... As coded, an injection point could be loaded into the local cache without the LWLock InjectionPointLock taken, hence a point detached and re-attached concurrently of a point running calling InjectionPointRun() may finish by loading a callback it did no set initially. Based on all the cases discussed until now on the lists, it is fine to delay the lock release until the callback is run, so let's do that. While on it, remove a useless LWLockRelease() called before an error in InjectionPointAttach(). Per discussion with Heikki Linnakangas and Noah Misch. Discussion: https://postgr.es/m/e1ffb822-054e-4006-ac06-50532767f75b@iki.fi	2 years ago
Michael Paquier	33181b48fd	Introduce private data area for injection points ... This commit extends the backend-side infrastructure of injection points so as it becomes possible to register some input data when attaching a point. This private data can be registered with the function name and the library name of the callback when attaching a point, then it is given as input argument to the callback. This gives the possibility for modules to pass down custom data at runtime when attaching a point without managing that internally, in a manner consistent with the callback entry retrieved from the hash shmem table storing the injection point data. InjectionPointAttach() gains two arguments, to be able to define the private data contents and its size. A follow-up commit will rely on this infrastructure to close a race condition with the injection point detach in the module injection_points. While on it, this changes InjectionPointDetach() to return a boolean, returning false if a point cannot be detached. This has been mentioned by Noah as useful when it comes to implement more complex tests with concurrent point detach, solid with the automatic detach done for local points in the test module. Documentation is adjusted in consequence. Per discussion with Noah Misch. Reviewed-by: Noah Misch Discussion: https://postgr.es/m/20240509031553.47@rfd.leadboat.com	2 years ago
Michael Paquier	cdd863480c	Fix ERROR message in injection_point.c ... This commit fixes an error message that failed to show the correct function and library names when a function cannot be loaded. While on it, adjust the call to load_external_function() so as this ERROR can be reached, by making load_external_function() return NULL rather than fail if a function cannot be found for a given injection point. Thinkos in d86d20f0ba.	2 years ago
Heikki Linnakangas	0eb23285a2	Fix two memcpy() bugs in the new injection point code ... 1. The memcpy()s in InjectionPointAttach() would copy garbage from beyond the end of input string to the buffer in shared memory. You won't usually notice, but if there is not enough valid mapped memory beyond the end of the string, the read of unmapped memory will segfault. This was flagged by the Cirrus CI build with address sanitizer enabled. 2. The memcpy() in injection_point_cache_add() failed to copy the NULL terminator. Discussion: https://www.postgresql.org/message-id/0615a424-b726-4157-afa7-4245629f9512%40iki.fi	2 years ago
Michael Paquier	d86d20f0ba	Add backend support for injection points ... Injection points are a new facility that makes possible for developers to run custom code in pre-defined code paths. Its goal is to provide ways to design and run advanced tests, for cases like: - Race conditions, where processes need to do actions in a controlled ordered manner. - Forcing a state, like an ERROR, FATAL or even PANIC for OOM, to force recovery, etc. - Arbitrary sleeps. This implements some basics, and there are plans to extend it more in the future depending on what's required. Hence, this commit adds a set of routines in the backend that allows developers to attach, detach and run injection points: - A code path calling an injection point can be declared with the macro INJECTION_POINT(name). - InjectionPointAttach() and InjectionPointDetach() to respectively attach and detach a callback to/from an injection point. An injection point name is registered in a shmem hash table with a library name and a function name, which will be used to load the callback attached to an injection point when its code path is run. Injection point names are just strings, so as an injection point can be declared and run by out-of-core extensions and modules, with callbacks defined in external libraries. This facility is hidden behind a dedicated switch for ./configure and meson, disabled by default. Note that backends use a local cache to store callbacks already loaded, cleaning up their cache if a callback has found to be removed on a best-effort basis. This could be refined further but any tests but what we have here was fine with the tests I've written while implementing these backend APIs. Author: Michael Paquier, with doc suggestions from Ashutosh Bapat. Reviewed-by: Ashutosh Bapat, Nathan Bossart, Álvaro Herrera, Dilip Kumar, Amul Sul, Nazir Bilal Yavuz Discussion: https://postgr.es/m/ZTiV8tn_MIb_H2rE@paquier.xyz	2 years ago