SERVER-31293 Don't consider readPreference 'primary' as equivalent to 'slaveOk' in OP_QUERY find path

jstests/replsets/slaveok_read_pref.js

@@ -0,0 +1,54 @@
+// Test that slaveOk is implicitly allowed for queries on a secondary with a read preference other
+// than 'primary', and that queries which do have 'primary' read preference fail.
+(function() {
+    "use strict";
+
+    const readPrefs =
+        [undefined, "primary", "secondary", "primaryPreferred", "secondaryPreferred", "nearest"];
+
+    const rst = new ReplSetTest({nodes: 3});
+    rst.startSet();
+
+    const nodes = rst.nodeList();
+    rst.initiate({
+        _id: jsTestName(),
+        members: [
+            {_id: 0, host: nodes[0]},
+            {_id: 1, host: nodes[1], priority: 0},
+            {_id: 2, host: nodes[2], arbiterOnly: true}
+        ]
+    });
+
+    const priDB = rst.getPrimary().getDB(jsTestName());
+    assert(priDB.dropDatabase());
+
+    assert.commandWorked(priDB.test.insert({a: 1}, {writeConcern: {w: "majority"}}));
+
+    const secDB = rst.getSecondary().getDB(jsTestName());
+
+    for (let readMode of["commands", "legacy"]) {
+        for (let readPref of readPrefs) {
+            for (let slaveOk of[true, false]) {
+                const testType = {readMode: readMode, readPref: readPref, slaveOk: slaveOk};
+
+                secDB.getMongo().forceReadMode(readMode);
+                secDB.getMongo().setSlaveOk(slaveOk);
+
+                const cursor =
+                    (readPref ? secDB.test.find().readPref(readPref) : secDB.test.find());
+
+                if (readPref === "primary" || (!readPref && !slaveOk)) {
+                    // Attempting to run the query throws an error of type NotMasterNoSlaveOk.
+                    const slaveOkErr = assert.throws(() => cursor.itcount(), [], testType);
+                    assert.commandFailedWithCode(slaveOkErr, ErrorCodes.NotMasterNoSlaveOk);
+                } else {
+                    // Succeeds for all non-primary readPrefs, and for no readPref iff slaveOk.
+                    const docCount = assert.doesNotThrow(() => cursor.itcount(), [], testType);
+                    assert.eq(docCount, 1);
+                }
+            }
+        }
+    }
+
+    rst.stopSet();
+})();

src/mongo/db/query/find.cpp

@@ -562,9 +562,12 @@ std::string runQuery(OperationContext* opCtx,
     {
         const QueryRequest& qr = cq->getQueryRequest();
 
-        // uassert if we are not on a primary, and not a secondary with SlaveOk query parameter set.
-        // TODO(SERVER-31293): Don't set slaveOk for reads with a read pref of "primary".
-        const bool slaveOK = qr.isSlaveOk() || qr.hasReadPref();
+        // Allow the query to run on secondaries if the read preference permits it. If no read
+        // preference was specified, allow the query to run iff slaveOk has been set.
+        const bool slaveOK = qr.hasReadPref()
+            ? uassertStatusOK(ReadPreferenceSetting::fromContainingBSON(q.query))
+                  .canRunOnSecondary()
+            : qr.isSlaveOk();
         uassertStatusOK(
             repl::ReplicationCoordinator::get(opCtx)->checkCanServeReadsFor(opCtx, nss, slaveOK));
     }