+ workqueue-avoid-recursion-in-run_workqueue.patch added to -mm tree

[akpm@xxxxxxxxxxxxxxxxxxxx]

The patch titled
     workqueue: avoid recursion in run_workqueue()
has been added to the -mm tree.  Its filename is
     workqueue-avoid-recursion-in-run_workqueue.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this

The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/

------------------------------------------------------
Subject: workqueue: avoid recursion in run_workqueue()
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>

1) lockdep will complain when run_workqueue() performs recursion.

2) The recursive implementation of run_workqueue() means that
   flush_workqueue() and its documentation are inconsistent.  This may
   hide deadlocks and other bugs.

3) The recursion in run_workqueue() will poison cwq->current_work, but
   flush_work() and __cancel_work_timer(), etcetera need a reliable
   cwq->current_work.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/workqueue.c |   41 +++++++++++------------------------------
 1 file changed, 11 insertions(+), 30 deletions(-)

diff -puN kernel/workqueue.c~workqueue-avoid-recursion-in-run_workqueue kernel/workqueue.c
--- a/kernel/workqueue.c~workqueue-avoid-recursion-in-run_workqueue
+++ a/kernel/workqueue.c
@@ -49,8 +49,6 @@ struct cpu_workqueue_struct {
 
 	struct workqueue_struct *wq;
 	struct task_struct *thread;
-
-	int run_depth;		/* Detect run_workqueue() recursion depth */
 } ____cacheline_aligned;
 
 /*
@@ -269,13 +267,6 @@ DEFINE_TRACE(workqueue_execution);
 static void run_workqueue(struct cpu_workqueue_struct *cwq)
 {
 	spin_lock_irq(&cwq->lock);
-	cwq->run_depth++;
-	if (cwq->run_depth > 3) {
-		/* morton gets to eat his hat */
-		printk("%s: recursion depth exceeded: %d\n",
-			__func__, cwq->run_depth);
-		dump_stack();
-	}
 	while (!list_empty(&cwq->worklist)) {
 		struct work_struct *work = list_entry(cwq->worklist.next,
 						struct work_struct, entry);
@@ -318,7 +309,6 @@ static void run_workqueue(struct cpu_wor
 		spin_lock_irq(&cwq->lock);
 		cwq->current_work = NULL;
 	}
-	cwq->run_depth--;
 	spin_unlock_irq(&cwq->lock);
 }
 
@@ -375,29 +365,20 @@ static void insert_wq_barrier(struct cpu
 
 static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
 {
-	int active;
+	int active = 0;
+	struct wq_barrier barr;
 
-	if (cwq->thread == current) {
-		/*
-		 * Probably keventd trying to flush its own queue. So simply run
-		 * it by hand rather than deadlocking.
-		 */
-		run_workqueue(cwq);
-		active = 1;
-	} else {
-		struct wq_barrier barr;
+	WARN_ON(cwq->thread == current);
 
-		active = 0;
-		spin_lock_irq(&cwq->lock);
-		if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
-			insert_wq_barrier(cwq, &barr, &cwq->worklist);
-			active = 1;
-		}
-		spin_unlock_irq(&cwq->lock);
-
-		if (active)
-			wait_for_completion(&barr.done);
+	spin_lock_irq(&cwq->lock);
+	if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
+		insert_wq_barrier(cwq, &barr, &cwq->worklist);
+		active = 1;
 	}
+	spin_unlock_irq(&cwq->lock);
+
+	if (active)
+		wait_for_completion(&barr.done);
 
 	return active;
 }
_

Patches currently in -mm which might be from laijs@xxxxxxxxxxxxxx are

linux-next.patch
workqueue-avoid-recursion-in-run_workqueue.patch
cpu-hotplug-remove-unused-cpuhotplug_mutex_lock.patch

--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html