1 files changed, 43 insertions, 10 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ca937b0c3a96..ab3c0dc8c7ed 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2091,8 +2091,30 @@ __acquires(&pool->lock)
 
         spin_unlock_irq(&pool->lock);
 
-        lock_map_acquire_read(&pwq->wq->lockdep_map);
+        lock_map_acquire(&pwq->wq->lockdep_map);
         lock_map_acquire(&lockdep_map);
+        /*
+         * Strictly speaking we should mark the invariant state without holding
+         * any locks, that is, before these two lock_map_acquire()'s.
+         *
+         * However, that would result in:
+         *
+         *   A(W1)
+         *   WFC(C)
+         *              A(W1)
+         *              C(C)
+         *
+         * Which would create W1->C->W1 dependencies, even though there is no
+         * actual deadlock possible. There are two solutions, using a
+         * read-recursive acquire on the work(queue) 'locks', but this will then
+         * hit the lockdep limitation on recursive locks, or simply discard
+         * these locks.
+         *
+         * AFAICT there is no possible deadlock scenario between the
+         * flush_work() and complete() primitives (except for single-threaded
+         * workqueues), so hiding them isn't a problem.
+         */
+        lockdep_invariant_state(true);
         trace_workqueue_execute_start(work);
         worker->current_func(work);
         /*
@@ -2474,7 +2496,16 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
          */
         INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
         __set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
-        init_completion(&barr->done);
+
+        /*
+         * Explicitly init the crosslock for wq_barrier::done, make its lock
+         * key a subkey of the corresponding work. As a result we won't
+         * build a dependency between wq_barrier::done and unrelated work.
+         */
+        lockdep_init_map_crosslock((struct lockdep_map *)&barr->done.map,
+                                   "(complete)wq_barr::done",
+                                   target->lockdep_map.key, 1);
+        __init_completion(&barr->done);
         barr->task = current;
 
         /*
@@ -2815,16 +2846,18 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
         spin_unlock_irq(&pool->lock);
 
         /*
-         * If @max_active is 1 or rescuer is in use, flushing another work
-         * item on the same workqueue may lead to deadlock.  Make sure the
-         * flusher is not running on the same workqueue by verifying write
-         * access.
+         * Force a lock recursion deadlock when using flush_work() inside a
+         * single-threaded or rescuer equipped workqueue.
+         *
+         * For single threaded workqueues the deadlock happens when the work
+         * is after the work issuing the flush_work(). For rescuer equipped
+         * workqueues the deadlock happens when the rescuer stalls, blocking
+         * forward progress.
          */
-        if (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)
+        if (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer) {
                 lock_map_acquire(&pwq->wq->lockdep_map);
-        else
-                lock_map_acquire_read(&pwq->wq->lockdep_map);
-        lock_map_release(&pwq->wq->lockdep_map);
+                lock_map_release(&pwq->wq->lockdep_map);
+        }
 
         return true;
 already_gone: