From 8d4850ae65b5ca314a540090bd94714cf327b71b Mon Sep 17 00:00:00 2001
From: Eliot Horowitz <eliot@10gen.com>
Date: Thu, 17 Feb 2011 19:59:33 -0500
Subject: detect clock skew in DistributedLock SERVER-2584

---
 client/distlock.cpp | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

(limited to 'client')

diff --git a/client/distlock.cpp b/client/distlock.cpp
index 307ae971f73..9ec98eaed18 100644
--- a/client/distlock.cpp
+++ b/client/distlock.cpp
@@ -182,7 +182,7 @@ namespace mongo {
 
         {
             // make sure its there so we can use simple update logic below
-            BSONObj o = conn->findOne( _ns , _id );
+            BSONObj o = conn->findOne( _ns , _id ).getOwned();
             if ( o.isEmpty() ) {
                 try {
                     log(4) << "dist_lock inserting initial doc in " << _ns << " for lock " << _name << endl;
@@ -192,32 +192,41 @@ namespace mongo {
                     log() << "dist_lock could not insert initial doc: " << e << endl;
                 }
             }
-
+            
             else if ( o["state"].numberInt() > 0 ) {
                 BSONObj lastPing = conn->findOne( lockPingNS , o["process"].wrap( "_id" ) );
                 if ( lastPing.isEmpty() ) {
                     // if a lock is taken but there's no ping for it, we're in an inconsistent situation
                     // if the lock holder (mongos or d)  does not exist anymore, the lock could safely be removed
                     // but we'd require analysis of the situation before a manual intervention
-                    log(LL_ERROR) << "config.locks: " << _name << " lock is taken by old process? "
-                                  << "remove the following lock if the process is not active anymore: " << o << endl;
+                    error() << "config.locks: " << _name << " lock is taken by old process? "
+                            << "remove the following lock if the process is not active anymore: " << o << endl;
                     *other = o;
-                    other->getOwned();
                     conn.done();
                     return false;
                 }
 
-                unsigned long long elapsed = jsTime() - lastPing["ping"].Date(); // in ms
+                unsigned long long now = jsTime();
+                unsigned long long pingTime = lastPing["ping"].Date();
+                
+                if ( now < pingTime ) {
+                    // clock skew
+                    warning() << "dist_lock has detected clock skew of " << ( pingTime - now ) << "ms" << endl;
+                    *other = o;
+                    conn.done();
+                    return false;
+                }
+                
+                unsigned long long elapsed = now - pingTime;
                 elapsed = elapsed / ( 1000 * 60 ); // convert to minutes
                 
                 if ( elapsed > ( 60 * 24 * 365 * 100 ) /* 100 years */ ) {
                     warning() << "distlock elapsed time seems impossible: " << lastPing << endl;
                 }
-
+                
                 if ( elapsed <= _takeoverMinutes ) {
                     log(1) << "dist_lock lock failed because taken by: " << o << " elapsed minutes: " << elapsed << endl;
                     *other = o;
-                    other->getOwned();
                     conn.done();
                     return false;
                 }
@@ -226,8 +235,8 @@ namespace mongo {
                 conn->update( _ns , _id , BSON( "$set" << BSON( "state" << 0 ) ) );
                 string err = conn->getLastError();
                 if ( ! err.empty() ) {
-                    log( LL_WARNING ) << "dist_lock take over from: " << o << " failed: " << err << endl;
-                    *other = o;
+                    warning() << "dist_lock take over from: " << o << " failed: " << err << endl;
+                    *other = o.getOwned();
                     other->getOwned();
                     conn.done();
                     return false;
-- 
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