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authorTejun Heo <tj@kernel.org>2011-01-09 23:32:15 +0100
committerTejun Heo <tj@kernel.org>2011-01-11 15:33:01 +0100
commite159489baa717dbae70f9903770a6a4990865887 (patch)
tree6e2ae803ff6ebed558ebbe03bf3ae5bda1dd6ebc
parent0c21e3aaf6ae85bee804a325aa29c325209180fd (diff)
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workqueue: relax lockdep annotation on flush_work()
Currently, the lockdep annotation in flush_work() requires exclusive access on the workqueue the target work is queued on and triggers warning if a work is trying to flush another work on the same workqueue; however, this is no longer true as workqueues can now execute multiple works concurrently. This patch adds lock_map_acquire_read() and make process_one_work() hold read access to the workqueue while executing a work and start_flush_work() check for write access if concurrnecy level is one or the workqueue has a rescuer (as only one execution resource - the rescuer - is guaranteed to be available under memory pressure), and read access if higher. This better represents what's going on and removes spurious lockdep warnings which are triggered by fake dependency chain created through flush_work(). * Peter pointed out that flushing another work from a WQ_MEM_RECLAIM wq breaks forward progress guarantee under memory pressure. Condition check accordingly updated. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: "Rafael J. Wysocki" <rjw@sisk.pl> Tested-by: "Rafael J. Wysocki" <rjw@sisk.pl> Cc: Peter Zijlstra <peterz@infradead.org> Cc: stable@kernel.org
-rw-r--r--include/linux/lockdep.h3
-rw-r--r--kernel/workqueue.c14
2 files changed, 15 insertions, 2 deletions
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 71c09b26c759..9f19430c7d07 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -522,12 +522,15 @@ static inline void print_irqtrace_events(struct task_struct *curr)
#ifdef CONFIG_DEBUG_LOCK_ALLOC
# ifdef CONFIG_PROVE_LOCKING
# define lock_map_acquire(l) lock_acquire(l, 0, 0, 0, 2, NULL, _THIS_IP_)
+# define lock_map_acquire_read(l) lock_acquire(l, 0, 0, 2, 2, NULL, _THIS_IP_)
# else
# define lock_map_acquire(l) lock_acquire(l, 0, 0, 0, 1, NULL, _THIS_IP_)
+# define lock_map_acquire_read(l) lock_acquire(l, 0, 0, 2, 1, NULL, _THIS_IP_)
# endif
# define lock_map_release(l) lock_release(l, 1, _THIS_IP_)
#else
# define lock_map_acquire(l) do { } while (0)
+# define lock_map_acquire_read(l) do { } while (0)
# define lock_map_release(l) do { } while (0)
#endif
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 8ee6ec82f88a..930c2390b77e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1840,7 +1840,7 @@ __acquires(&gcwq->lock)
spin_unlock_irq(&gcwq->lock);
work_clear_pending(work);
- lock_map_acquire(&cwq->wq->lockdep_map);
+ lock_map_acquire_read(&cwq->wq->lockdep_map);
lock_map_acquire(&lockdep_map);
trace_workqueue_execute_start(work);
f(work);
@@ -2384,8 +2384,18 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
insert_wq_barrier(cwq, barr, work, worker);
spin_unlock_irq(&gcwq->lock);
- lock_map_acquire(&cwq->wq->lockdep_map);
+ /*
+ * 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.
+ */
+ if (cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER)
+ lock_map_acquire(&cwq->wq->lockdep_map);
+ else
+ lock_map_acquire_read(&cwq->wq->lockdep_map);
lock_map_release(&cwq->wq->lockdep_map);
+
return true;
already_gone:
spin_unlock_irq(&gcwq->lock);