diff --git a/src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java b/src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java
index fb759052df2..c58a789985e 100644
--- a/src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java
+++ b/src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java
@@ -1428,53 +1428,58 @@ public class ForkJoinPool extends AbstractExecutorService
         /**
          * Runs the given task, as well as remaining local tasks, and
          * those from the given queue that can be polled without interference.
+         *
+         * @param task the top-level task
+         * @param q the WorkQueue from which task was taken
+         * @param fifo nonzero if fifo mode
+         * @param qbase the next base index of q to take;
+         *        returning if no such task or already taken
+         * @return number of top-level tasks stolen from q
          */
         final int topLevelExec(ForkJoinTask<?> task, WorkQueue q,
                                 int fifo, int qbase) {
+            if (task == null || q == null)
+                return 0;        // currently impossible
             int stolen = 1;
-            if (task != null && q != null) {
-                outer: for (;;) {
-                    task.doExec();
-                    task = null;
-                    int p = top, cap; ForkJoinTask<?>[] a;
-                    if ((a = array) == null || (cap = a.length) <= 0)
-                        break;
-                    if (fifo == 0) {  // specialized localPop
-                        int s = p - 1; long k;
-                        if (U.getReference(
-                                a, k = slotOffset((cap - 1) & s)) != null &&
-                            (task = (ForkJoinTask<?>)
-                             U.getAndSetReference(a, k, null)) != null) {
-                            top = s;
-                            continue;
-                        }
-                    } else {         // specialized localPoll
-                        for (int b = base; p - b > 0; ) {
-                            int nb = b + 1;
-                            if ((task = (ForkJoinTask<?>)U.getAndSetReference(
-                                     a, slotOffset((cap - 1) & b), null)) != null) {
-                                base = nb;
-                                continue outer;
-                            }
-                            if (nb == p)
-                                break;
-                            while (b == (b = U.getIntAcquire(this, BASE)))
-                                Thread.onSpinWait();
-                        }
+            outer: for (;;) {
+                task.doExec();
+                task = null;
+                int p = top, cap; ForkJoinTask<?>[] a;
+                if ((a = array) == null || (cap = a.length) <= 0)
+                    break;        // currently impossible
+                if (fifo == 0) {  // specialized localPop
+                    int s = p - 1; long k;
+                    if (U.getReference(
+                            a, k = slotOffset((cap - 1) & s)) != null &&
+                        (task = (ForkJoinTask<?>)
+                         U.getAndSetReference(a, k, null)) != null) {
+                        top = s;
+                        continue;
+                    }
+                } else {         // specialized localPoll
+                    for (int b = base; p - b > 0; ) {
+                        int nb = b + 1;
+                        if ((task = (ForkJoinTask<?>)U.getAndSetReference(
+                                 a, slotOffset((cap - 1) & b), null)) != null) {
+                            base = nb;
+                            continue outer;
+                        }
+                        if (nb == p)
+                            break;
+                        while (b == (b = U.getIntAcquire(this, BASE)))
+                            Thread.onSpinWait();
                     }
-                    // one-shot steal attempt
-                    ForkJoinTask<?> t; int qcap; long qk;
-                    ForkJoinTask<?>[] qa = q.array;
-                    if (q.base != qbase || qa == null || (qcap = qa.length) <= 0 ||
-                        (t = (ForkJoinTask<?>)U.getReferenceAcquire(
-                            qa, qk = slotOffset((qcap - 1) & qbase))) == null ||
-                        q.base != qbase ||
-                        !U.compareAndSetReference(qa, qk, t, null))
-                        break;
-                    q.base = ++qbase;
-                    ++stolen;
-                    task = t;
                 }
+                // try (once) to steal at q's next base index
+                ForkJoinTask<?>[] qa = q.array; int qcap; long qk;
+                if (q.base != qbase || qa == null || (qcap = qa.length) <= 0 ||
+                    (task = (ForkJoinTask<?>)U.getReferenceAcquire(
+                        qa, qk = slotOffset((qcap - 1) & qbase))) == null ||
+                    q.base != qbase || // ensure valid read
+                    !U.compareAndSetReference(qa, qk, task, null))
+                    break;
+                q.base = ++qbase;
+                ++stolen;
             }
             return stolen;
         }
@@ -1896,6 +1901,9 @@ public class ForkJoinPool extends AbstractExecutorService
     /**
      * Releases an idle worker, or creates one if not enough exist,
      * giving up q is nonull and signalled slot already taken.
+     *
+     * @param q, if nonnull, the WorkQueue containing signalled task
+     * @param qbase q's base index for the task
      */
     final void signalWork(WorkQueue q, int qbase) {
         int pc = parallelism;
@@ -1920,7 +1928,7 @@ public class ForkJoinPool extends AbstractExecutorService
             else
                 nc = (v.stackPred & LMASK) | (c & TC_MASK) | ac;
             if (q != null && q.base - qbase > 0)
-                    break;
+                break;
             if (c == (c = ctl) && c == (c = compareAndExchangeCtl(c, nc))) {
                 if (v == null)
                     createWorker();