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Fix race in triggers for read/write locks. (#15933)

This commit is contained in:
Erik Johnston 2023-07-19 12:06:38 +01:00 committed by GitHub
parent cb6e2c6cc7
commit 40a3583ba1
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GPG key ID: 4AEE18F83AFDEB23
5 changed files with 135 additions and 98 deletions

1
changelog.d/15933.misc Normal file
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@ -0,0 +1 @@
Fix bug with read/write lock implementation. This is currently unused so has no observable effects.

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@ -99,54 +99,3 @@ CREATE UNIQUE INDEX worker_read_write_locks_write ON worker_read_write_locks (lo
-- constraints.
ALTER TABLE worker_read_write_locks_mode ADD CONSTRAINT worker_read_write_locks_mode_foreign
FOREIGN KEY (lock_name, lock_key, token) REFERENCES worker_read_write_locks(lock_name, lock_key, token) DEFERRABLE INITIALLY DEFERRED;
-- Add a trigger to UPSERT into `worker_read_write_locks_mode` whenever we try
-- and acquire a lock, i.e. insert into `worker_read_write_locks`,
CREATE OR REPLACE FUNCTION upsert_read_write_lock_parent() RETURNS trigger AS $$
BEGIN
INSERT INTO worker_read_write_locks_mode (lock_name, lock_key, write_lock, token)
VALUES (NEW.lock_name, NEW.lock_key, NEW.write_lock, NEW.token)
ON CONFLICT (lock_name, lock_key)
DO NOTHING;
RETURN NEW;
END
$$
LANGUAGE plpgsql;
CREATE TRIGGER upsert_read_write_lock_parent_trigger BEFORE INSERT ON worker_read_write_locks
FOR EACH ROW
EXECUTE PROCEDURE upsert_read_write_lock_parent();
-- Ensure that we keep `worker_read_write_locks_mode` up to date whenever a lock
-- is released (i.e. a row deleted from `worker_read_write_locks`). Either we
-- update the `worker_read_write_locks_mode.token` to match another instance
-- that has currently acquired the lock, or we delete the row if nobody has
-- currently acquired a lock.
CREATE OR REPLACE FUNCTION delete_read_write_lock_parent() RETURNS trigger AS $$
DECLARE
new_token TEXT;
BEGIN
SELECT token INTO new_token FROM worker_read_write_locks
WHERE
lock_name = OLD.lock_name
AND lock_key = OLD.lock_key;
IF NOT FOUND THEN
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
ELSE
UPDATE worker_read_write_locks_mode
SET token = new_token
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
END IF;
RETURN NEW;
END
$$
LANGUAGE plpgsql;
CREATE TRIGGER delete_read_write_lock_parent_trigger AFTER DELETE ON worker_read_write_locks
FOR EACH ROW
EXECUTE PROCEDURE delete_read_write_lock_parent();

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@ -70,50 +70,3 @@ CREATE TABLE worker_read_write_locks (
CREATE UNIQUE INDEX worker_read_write_locks_key ON worker_read_write_locks (lock_name, lock_key, token);
-- Ensures that only one instance can acquire a lock in write mode at a time.
CREATE UNIQUE INDEX worker_read_write_locks_write ON worker_read_write_locks (lock_name, lock_key) WHERE write_lock;
-- Add a trigger to UPSERT into `worker_read_write_locks_mode` whenever we try
-- and acquire a lock, i.e. insert into `worker_read_write_locks`,
CREATE TRIGGER IF NOT EXISTS upsert_read_write_lock_parent_trigger
BEFORE INSERT ON worker_read_write_locks
FOR EACH ROW
BEGIN
-- First ensure that `worker_read_write_locks_mode` doesn't have stale
-- entries in it, as on SQLite we don't have the foreign key constraint to
-- enforce this.
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = NEW.lock_name AND lock_key = NEW.lock_key
AND NOT EXISTS (
SELECT 1 FROM worker_read_write_locks
WHERE lock_name = NEW.lock_name AND lock_key = NEW.lock_key
);
INSERT INTO worker_read_write_locks_mode (lock_name, lock_key, write_lock, token)
VALUES (NEW.lock_name, NEW.lock_key, NEW.write_lock, NEW.token)
ON CONFLICT (lock_name, lock_key)
DO NOTHING;
END;
-- Ensure that we keep `worker_read_write_locks_mode` up to date whenever a lock
-- is released (i.e. a row deleted from `worker_read_write_locks`). Either we
-- update the `worker_read_write_locks_mode.token` to match another instance
-- that has currently acquired the lock, or we delete the row if nobody has
-- currently acquired a lock.
CREATE TRIGGER IF NOT EXISTS delete_read_write_lock_parent_trigger
AFTER DELETE ON worker_read_write_locks
FOR EACH ROW
BEGIN
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
AND NOT EXISTS (
SELECT 1 FROM worker_read_write_locks
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
);
UPDATE worker_read_write_locks_mode
SET token = (
SELECT token FROM worker_read_write_locks
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
)
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
END;

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@ -0,0 +1,69 @@
/* Copyright 2023 The Matrix.org Foundation C.I.C
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
-- Fix up the triggers that were in `78/04_read_write_locks_triggers.sql`
-- Add a trigger to UPSERT into `worker_read_write_locks_mode` whenever we try
-- and acquire a lock, i.e. insert into `worker_read_write_locks`,
CREATE OR REPLACE FUNCTION upsert_read_write_lock_parent() RETURNS trigger AS $$
BEGIN
INSERT INTO worker_read_write_locks_mode (lock_name, lock_key, write_lock, token)
VALUES (NEW.lock_name, NEW.lock_key, NEW.write_lock, NEW.token)
ON CONFLICT (lock_name, lock_key)
DO UPDATE SET write_lock = NEW.write_lock, token = NEW.token;
RETURN NEW;
END
$$
LANGUAGE plpgsql;
DROP TRIGGER IF EXISTS upsert_read_write_lock_parent_trigger ON worker_read_write_locks;
CREATE TRIGGER upsert_read_write_lock_parent_trigger BEFORE INSERT ON worker_read_write_locks
FOR EACH ROW
EXECUTE PROCEDURE upsert_read_write_lock_parent();
-- Ensure that we keep `worker_read_write_locks_mode` up to date whenever a lock
-- is released (i.e. a row deleted from `worker_read_write_locks`). Either we
-- update the `worker_read_write_locks_mode.token` to match another instance
-- that has currently acquired the lock, or we delete the row if nobody has
-- currently acquired a lock.
CREATE OR REPLACE FUNCTION delete_read_write_lock_parent() RETURNS trigger AS $$
DECLARE
new_token TEXT;
BEGIN
SELECT token INTO new_token FROM worker_read_write_locks
WHERE
lock_name = OLD.lock_name
AND lock_key = OLD.lock_key
LIMIT 1 FOR UPDATE;
IF NOT FOUND THEN
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key AND token = OLD.token;
ELSE
UPDATE worker_read_write_locks_mode
SET token = new_token
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
END IF;
RETURN NEW;
END
$$
LANGUAGE plpgsql;
DROP TRIGGER IF EXISTS delete_read_write_lock_parent_trigger ON worker_read_write_locks;
CREATE TRIGGER delete_read_write_lock_parent_trigger AFTER DELETE ON worker_read_write_locks
FOR EACH ROW
EXECUTE PROCEDURE delete_read_write_lock_parent();

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@ -0,0 +1,65 @@
/* Copyright 2023 The Matrix.org Foundation C.I.C
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
-- Fix up the triggers that were in `78/04_read_write_locks_triggers.sql`
-- Add a trigger to UPSERT into `worker_read_write_locks_mode` whenever we try
-- and acquire a lock, i.e. insert into `worker_read_write_locks`,
DROP TRIGGER IF EXISTS upsert_read_write_lock_parent_trigger;
CREATE TRIGGER IF NOT EXISTS upsert_read_write_lock_parent_trigger
BEFORE INSERT ON worker_read_write_locks
FOR EACH ROW
BEGIN
-- First ensure that `worker_read_write_locks_mode` doesn't have stale
-- entries in it, as on SQLite we don't have the foreign key constraint to
-- enforce this.
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = NEW.lock_name AND lock_key = NEW.lock_key
AND NOT EXISTS (
SELECT 1 FROM worker_read_write_locks
WHERE lock_name = NEW.lock_name AND lock_key = NEW.lock_key
);
INSERT INTO worker_read_write_locks_mode (lock_name, lock_key, write_lock, token)
VALUES (NEW.lock_name, NEW.lock_key, NEW.write_lock, NEW.token)
ON CONFLICT (lock_name, lock_key)
DO UPDATE SET write_lock = NEW.write_lock, token = NEW.token;
END;
-- Ensure that we keep `worker_read_write_locks_mode` up to date whenever a lock
-- is released (i.e. a row deleted from `worker_read_write_locks`). Either we
-- update the `worker_read_write_locks_mode.token` to match another instance
-- that has currently acquired the lock, or we delete the row if nobody has
-- currently acquired a lock.
DROP TRIGGER IF EXISTS delete_read_write_lock_parent_trigger;
CREATE TRIGGER IF NOT EXISTS delete_read_write_lock_parent_trigger
AFTER DELETE ON worker_read_write_locks
FOR EACH ROW
BEGIN
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
AND token = OLD.token
AND NOT EXISTS (
SELECT 1 FROM worker_read_write_locks
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
);
UPDATE worker_read_write_locks_mode
SET token = (
SELECT token FROM worker_read_write_locks
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
)
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
END;