Hi everyone,

I just realized I probably sent my original message (see below) to the wrong list. So here goes again, this time with a deeper understanding what is going on, but also still much doubt and confusion.

tl;dr on the original post: Users are being randomly disconnected from our mediawiki instances.

I would like to check with you if what I found is a bug or not and if it's not, then I'm looking to understand why it behaves this way. I am also looking for information on what triggers garbage collection of PHP sessions.

Since I originally posted, I have found out what is deleting sessions from the objectcache table in the database. I have been able to reproduce this both on a remote server and locally. Both times, my set-up is running in a docker environment.

The call-stack that does this is the following:

#0 SqlBagOStuff->deleteServerObjectsExpiringBefore() called at [/var/www/html/includes/objectcache/SqlBagOStuff.php:668] #1  SqlBagOStuff->deleteObjectsExpiringBefore() called at [/var/www/html/includes/libs/objectcache/CachedBagOStuff.php:148] #2  CachedBagOStuff->deleteObjectsExpiringBefore() called at [/var/www/html/includes/session/PHPSessionHandler.php:376] #3  MediaWiki\Session\PHPSessionHandler->gc() #4  session_start() called at [/var/www/html/includes/Setup.php:757] #5  require_once(/var/www/html/includes/Setup.php) called at [/var/www/html/includes/WebStart.php:89] #6  require(/var/www/html/includes/WebStart.php) called at [/var/www/html/index.php:44]

Usually, SqlBagOStuff::deleteServerObjectsExpiringBefore is called fromMWCallableUpdate->doUpdate() and passed a Unix timestamp. This timestamp is a UTC value and handled as such.

However, sometimes, as can be seen from the backtrace above, it is called from the Garbage Collector in PHPSessionHandler:

public function gc( $maxlifetime ) {     if ( self::$instance !== $this ) {         throw new \UnexpectedValueException( __METHOD__ . ': Wrong instance called!' );     }     $before = date( 'YmdHis', time() );     $this->store->deleteObjectsExpiringBefore( $before );     return true; }

The problem here is that – probably for historical reasons - the function is passed a date string here instead of a Unix timestamp. And *the actual problem with that* is that the date() function applies timezone information (if $wgLocaltimezone is set). The resulting timestamp will thus be in the future (or be local time, interpreted as UTC). With a value of something equivalent to GMT+2, gc() will cause all current sessions to be deleted since they have a standard expiry time of 1h, stored as UTC value in the database.

If this happens, and the session is not declared persistent ($session->isPersistent(), "Keep me logged in"), then all users are immediately logged out of mediawiki.

Thus, my first question: Is this a bug? Since the $timestamp parameter is passed to ConvertibleTimestamp::convert( TS_UNIX, $timestamp ) in SqlBagOStuff::deleteServerObjectsExpiringBefore anyway, I do not see any reason to pass a date string. My suggestion for a fix would be to change the gc method as follows:

public function gc( $maxlifetime ) {     if ( self::$instance !== $this ) {         throw new \UnexpectedValueException( __METHOD__ . ': Wrong instance called!' );     }     $this->store->deleteObjectsExpiringBefore( microtime(true) );    // time() would be sufficient     return true; }

My second question would be: What controls when PHPSessionHandler::gc is called? Is it indeed the session configuration for the PHP process (i.e. session.gc_probability, session.gc_divisor and session.gc_maxlifetime) ?

Thanks, David

Hi all,

I'm writing to the list in the hope of receiving some feedback, questions, maybe answers to help us solve a conundrum with sessions we have on our Wikibase/Mediawiki installation.

We're running two different docker-based wikibase installations (one staging, one production) on two separate virtual machines. Both use the SimpleSaml extension to connect to a SAML implementation, but we have found that the random session deletion happens both with and without the SAML extension used.

The symptoms that we've seen are that out of the blue, users are disconnected from mediawiki. Since we use SAML, it's enough to click the Login link to again be connected.

The duration or number of requests until a session is deleted seems random. It does appear though, that the more (or more frequent) requests are made (and thus background jobs run) the quicker a session is deleted.

We have even tried setting $wgObjectCacheSessionExpiry = 7200; in order to exclude any TimeZone related issues which was our first suspicion. However, changing this from the default 1h session expiry does not change the behavior we're seeing.

Sessions are deleted regardless of their nature. E.g. sessions established for oauth connections are deleted in the same way and at the same time as other sessions. E.g. using wikidataintegrator we're able to run a number of requests until the CSRF token expires (with the number of requests that succeed before this happens being random):

[…] Created Item Q379 from Classhttp://www.cidoc-crm.org/cidoc-crm/E34_Inscription. Created Item Q380 from Classhttp://www.cidoc-crm.org/cidoc-crm/E53_Place. Errorwhile writing to Wikidata ERROR creating class referencefor http://www.cidoc-crm.org/cidoc-crm/E35_Title: {'error': {'code':'badtoken','info':'Invalid CSRF token.','*':'See https://saf-dev.bnl.lu/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce%3E; for notice of API deprecations and breaking changes.'}} Errorwhile writing to Wikidata ERROR creating object property referencefor http://www.cidoc-crm.org/cidoc-crm/P16_used_specific_object: {'error': {'code':'badtoken','info':'Invalid CSRF token.','*':'See https://saf-dev.bnl.lu/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce%3E; for notice of API deprecations and breaking changes.'}}

If sessions are not randomly deleted, then session renewal seems to work as planned with them being renewed after half their expiry time:

|[DBQuery] SqlBagOStuff::fetchBlobMulti [0s] db.svc:3306: SELECT keyname,value,exptime FROM `objectcache` WHE RE keyname = 'mediawiki:MWSession:n9krnsfa303qk9c2osp6c81tp1k2bp5b' [session] SessionBackend "require/require_once/MediaWiki\Session\Session->renew/MediaWiki\Session\SessionBackend-

...

renew" metadata dirty for renew():

require/require_once/MediaWiki\Session\Session->renew/MediaWiki\Session\Sessi onBackend->renew [session] SessionBackend "n9krnsfa303qk9c2osp6c81tp1k2bp5b" force-persist for renew(): require/require_once/Media Wiki\Session\Session->renew/MediaWiki\Session\SessionBackend->renew [session] SessionBackend "n9krnsfa303qk9c2osp6c81tp1k2bp5b" save: dataDirty=0 metaDirty=1 forcePersist=1 [cookie] setcookie: "mediawiki_session", "n9krnsfa303qk9c2osp6c81tp1k2bp5b", "0", "/", "", "1", "1", "" [cookie] setcookie: "mediawikiUserID", "13", "1648233666", "/", "", "1", "1", "" [cookie] setcookie: "mediawikiUserName", "Ibl676", "1648233666", "/", "", "1", "1", "" [cookie] already deleted setcookie: "mediawikiToken", "", "1614105666", "/", "", "1", "1", "" [cookie] already deleted setcookie: "forceHTTPS", "", "1614105666", "/", "", "", "1", "" [session] SessionBackend "n9krnsfa303qk9c2osp6c81tp1k2bp5b" Taking over PHP session [session] SessionBackend "n9krnsfa303qk9c2osp6c81tp1k2bp5b" save: dataDirty=0 metaDirty=1 forcePersist=1 [cookie] already set setcookie: "mediawiki_session", "n9krnsfa303qk9c2osp6c81tp1k2bp5b", "0", "/", "", "1", "1", "" [cookie] already set setcookie: "mediawikiUserID", "13", "1648233666", "/", "", "1", "1", "" [cookie] already set setcookie: "mediawikiUserName", "Ibl676", "1648233666", "/", "", "1", "1", "" [cookie] already deleted setcookie: "mediawikiToken", "", "1614105666", "/", "", "1", "1", "" [cookie] already deleted setcookie: "forceHTTPS", "", "1614105666", "/", "", "", "1", "" [DBQuery] SqlBagOStuff::updateTable [0.002s] db.svc:3306: REPLACE INTO `objectcache` (keyname,value,exptime) VALU ES ('mediawiki:MWSession:n9krnsfa303qk9c2osp6c81tp1k2bp5b','...\0','20220223194106')|

Here is one example where the session got deleted by whatever feels responsible to do so:

MariaDB [mediawiki]> select keyname, exptimefrom objectcachewhere keynamelike 'mediawiki:MWSession%'; +------------------------------------------------------+---------------------+ | keyname | exptime | +------------------------------------------------------+---------------------+ | mediawiki:MWSession:t7d5lms2nrma6k627c6usrgc6289en3a |2022-03-24 17:34:34 | +------------------------------------------------------+---------------------+ 1 rowin set (0.001 sec)

MariaDB [mediawiki]> select keyname, exptimefrom objectcachewhere keynamelike 'mediawiki:MWSession%'; Emptyset (0.001 sec)

MariaDB [mediawiki]> select now(); +---------------------+ | now() | +---------------------+ |2022-03-24 17:37:15 | +---------------------+ 1 rowin set (0.024 sec)

The only instance of me finding something remotely related to randomly deleting a session would be these log entries:

|2022-03-24 17:03:29 51290acae35a mediawiki: SessionManager using store SqlBagOStuff 2022-03-24 17:03:29 51290acae35a mediawiki: Saving all sessions on shutdown 2022-03-24 17:03:29 51290acae35a mediawiki: SessionManager using store SqlBagOStuff 2022-03-24 17:03:29 51290acae35a mediawiki: Session "[30]MediaWiki\Session\CookieSessionProvider<-:13:Ibl676>8favvi92d08njut82j66un60r601titn": Unverified user provided and no metadata to auth it 2022-03-24 17:03:29 51290acae35a mediawiki: setcookie: "mediawiki_session", "", "1616605409", "/", "", "1", "1", "" 2022-03-24 17:03:29 51290acae35a mediawiki: setcookie: "mediawikiUserID", "", "1616605409", "/", "", "1", "1", "" 2022-03-24 17:03:29 51290acae35a mediawiki: already deleted setcookie: "mediawikiToken", "", "1616605409", "/", "", "1", "1", "" 2022-03-24 17:03:29 51290acae35a mediawiki: already deleted setcookie: "forceHTTPS", "", "1616605409", "/", "", "", "1", "" 2022-03-24 17:03:29 51290acae35a mediawiki: SessionBackend "ujf6rcheseb51lpaojrqggb4c23s1flr" is unsaved, marking dirty in constructor 2022-03-24 17:03:29 51290acae35a mediawiki: SessionBackend "ujf6rcheseb51lpaojrqggb4c23s1flr" save: dataDirty=1 metaDirty=1 forcePersist=0 2022-03-24 17:03:29 51290acae35a mediawiki: already deleted setcookie: "mediawiki_session", "", "1616605409", "/", "", "1", "1", "" 2022-03-24 17:03:29 51290acae35a mediawiki: already deleted setcookie: "mediawikiUserID", "", "1616605409", "/", "", "1", "1", "" 2022-03-24 17:03:29 51290acae35a mediawiki: already deleted setcookie: "mediawikiToken", "", "1616605409", "/", "", "1", "1", "" 2022-03-24 17:03:29 51290acae35a mediawiki: already deleted setcookie: "forceHTTPS", "", "1616605409", "/", "", "", "1", "" 2022-03-24 17:03:29 51290acae35a mediawiki: Saving all sessions on shutdown |

IBL676 is my SAML ID. I'm not sure why the user is unverified and what metadata would be used/required to verify it?

Looking forward to any advice on how to further investigate what is going on here.