Bug 987248 - Prevent divide-by-zero in seer. r=mcmanus

netwerk/base/src/Seer.cpp

@@ -125,6 +125,10 @@ struct SeerTelemetryAccumulators {
   Telemetry::AutoCounter<Telemetry::SEER_TOTAL_PRECONNECTS> mTotalPreconnects;
   Telemetry::AutoCounter<Telemetry::SEER_TOTAL_PRERESOLVES> mTotalPreresolves;
   Telemetry::AutoCounter<Telemetry::SEER_PREDICTIONS_CALCULATED> mPredictionsCalculated;
+  Telemetry::AutoCounter<Telemetry::SEER_LOAD_COUNT_IS_ZERO> mLoadCountZeroes;
+  Telemetry::AutoCounter<Telemetry::SEER_LOAD_COUNT_OVERFLOWS> mLoadCountOverflows;
+  Telemetry::AutoCounter<Telemetry::SEER_STARTUP_COUNT_IS_ZERO> mStartupCountZeroes;
+  Telemetry::AutoCounter<Telemetry::SEER_STARTUP_COUNT_OVERFLOWS> mStartupCountOverflows;
 };
 
 // Listener for the speculative DNS requests we'll fire off, which just ignores
@@ -654,6 +658,13 @@ Seer::EnsureInitStorage()
         getter_AddRefs(stmt));
     NS_ENSURE_SUCCESS(rv, rv);
 
+    int32_t newStartupCount = mStartupCount + 1;
+    if (newStartupCount <= 0) {
+      SEER_LOG(("Seer::EnsureInitStorage startup count overflow\n"));
+      newStartupCount = mStartupCount;
+      ++mAccumulators->mStartupCountOverflows;
+    }
+
     rv = stmt->BindInt32ByName(NS_LITERAL_CSTRING("startup_count"),
                                mStartupCount + 1);
     NS_ENSURE_SUCCESS(rv, rv);
@@ -1296,10 +1307,18 @@ Seer::UpdateTopLevel(QueryType queryType, const TopLevelInfo &info, PRTime now)
   }
   mozStorageStatementScoper scope(stmt);
 
+  int32_t newLoadCount = info.loadCount + 1;
+  if (newLoadCount <= 0) {
+    SEER_LOG(("Seer::UpdateTopLevel type %d id %d load count overflow\n",
+              queryType, info.id));
+    newLoadCount = info.loadCount;
+    ++mAccumulators->mLoadCountOverflows;
+  }
+
   // First, let's update the page in the database, since loading a page
   // implicitly learns about the page.
   nsresult rv = stmt->BindInt32ByName(NS_LITERAL_CSTRING("load_count"),
-                                      info.loadCount + 1);
+                                      newLoadCount);
   RETURN_IF_FAILED(rv);
 
   rv = stmt->BindInt64ByName(NS_LITERAL_CSTRING("now"), now);
@@ -1322,6 +1341,12 @@ Seer::TryPredict(QueryType queryType, const TopLevelInfo &info, PRTime now,
 {
   MOZ_ASSERT(!NS_IsMainThread(), "TryPredict called on main thread.");
 
+  if (!info.loadCount) {
+    SEER_LOG(("Seer::TryPredict info.loadCount is zero!\n"));
+    ++mAccumulators->mLoadCountZeroes;
+    return false;
+  }
+
   int globalDegradation = CalculateGlobalDegradation(now, info.lastLoad);
 
   // Now let's look up the subresources we know about for this page
@@ -1402,6 +1427,12 @@ Seer::WouldRedirect(const TopLevelInfo &info, PRTime now, UriInfo &newUri)
 {
   MOZ_ASSERT(!NS_IsMainThread(), "WouldRedirect called on main thread.");
 
+  if (!info.loadCount) {
+    SEER_LOG(("Seer::WouldRedirect info.loadCount is zero!\n"));
+    ++mAccumulators->mLoadCountZeroes;
+    return false;
+  }
+
   nsCOMPtr<mozIStorageStatement> stmt = mStatements.GetCachedStatement(
       NS_LITERAL_CSTRING("SELECT uri, origin, hits, last_hit "
                          "FROM moz_redirects WHERE pid = :id;"));
@@ -1532,6 +1563,12 @@ Seer::PredictForStartup(SeerVerifierHandle &verifier,
 {
   MOZ_ASSERT(!NS_IsMainThread(), "PredictForStartup called on main thread");
 
+  if (!mStartupCount) {
+    SEER_LOG(("Seer::PredictForStartup mStartupCount is zero!\n"));
+    ++mAccumulators->mStartupCountZeroes;
+    return;
+  }
+
   if (NS_FAILED(EnsureInitStorage())) {
     return;
   }

toolkit/components/telemetry/Histograms.json

@@ -2241,6 +2241,34 @@
       "kind": "boolean",
       "description": "Whether or not we actually try the cleanup method when we think about it"
   },
+  "SEER_LOAD_COUNT_IS_ZERO": {
+      "expires_in_version": "never",
+      "kind": "linear",
+      "high": "100",
+      "n_buckets": 50,
+      "description": "Number of times load count is zero"
+  },
+  "SEER_LOAD_COUNT_OVERFLOWS": {
+      "expires_in_version": "never",
+      "kind": "linear",
+      "high": "100",
+      "n_buckets": 50,
+      "description": "Number of times load count overflowed"
+  },
+  "SEER_STARTUP_COUNT_IS_ZERO": {
+      "expires_in_version": "never",
+      "kind": "linear",
+      "high": "100",
+      "n_buckets": 50,
+      "description": "Number of times startup count is zero"
+  },
+  "SEER_STARTUP_COUNT_OVERFLOWS": {
+      "expires_in_version": "never",
+      "kind": "linear",
+      "high": "100",
+      "n_buckets": 50,
+      "description": "Number of times startup count overflowed"
+  },
   "FIND_PLUGINS": {
     "expires_in_version": "never",
     "kind": "exponential",