Merge tag 'v3.6-rc7' into drm-intel-next-queued

Manual backmerge of -rc7 to resolve a silent conflict leading to
compile failure in drivers/gpu/drm/i915/intel_hdmi.c.

This is due to the bugfix in -rc7:

commit b98b60167279df3acac9422c3c9820d9ebbcf9fb
Author: Wang Xingchao <xingchao.wang@intel.com>
Date:   Thu Sep 13 07:43:22 2012 +0800

    drm/i915: HDMI - Clear Audio Enable bit for Hot Plug

Since this code moved around a lot in -next git put that snippet at
the wrong spot. I've tried to fix this by making the conflict explicit
by merging a version for next with:

commit 3cce574f0190dd149472059fb69267cf83d290f9
Author: Wang Xingchao <xingchao.wang@intel.com>
Date:   Thu Sep 13 11:19:00 2012 +0800

    drm/i915: HDMI - Clear Audio Enable bit for Hot Plug unconditionally

But that failed to solve the entire problem. To avoid pushing out
further -nightly branch to our QA where this is broken, do the
backmerge and manually add the stuff git adds to -next from the patch
in -fixes.

Note that this doesn't show up in git's merge diff (and hence is also
not handled by git rerere), which adds to the reasons why I'd like to
fix this with a verbose backmerge. The git merge diff only shows a
bunch of trivial conflicts of the "code changed in lines next to each
another" kind.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 107 insertions, 40 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 692d97628a1..3c5a79e2134 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -66,6 +66,7 @@ enum {
 
 	/* pool flags */
 	POOL_MANAGE_WORKERS	= 1 << 0,	/* need to manage workers */
+	POOL_MANAGING_WORKERS   = 1 << 1,       /* managing workers */
 
 	/* worker flags */
 	WORKER_STARTED		= 1 << 0,	/* started */
@@ -652,7 +653,7 @@ static bool need_to_manage_workers(struct worker_pool *pool)
 /* Do we have too many workers and should some go away? */
 static bool too_many_workers(struct worker_pool *pool)
 {
-	bool managing = mutex_is_locked(&pool->manager_mutex);
+	bool managing = pool->flags & POOL_MANAGING_WORKERS;
 	int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
 	int nr_busy = pool->nr_workers - nr_idle;
 
@@ -1326,6 +1327,15 @@ static void idle_worker_rebind(struct worker *worker)
 
 	/* we did our part, wait for rebind_workers() to finish up */
 	wait_event(gcwq->rebind_hold, !(worker->flags & WORKER_REBIND));
+
+	/*
+	 * rebind_workers() shouldn't finish until all workers passed the
+	 * above WORKER_REBIND wait.  Tell it when done.
+	 */
+	spin_lock_irq(&worker->pool->gcwq->lock);
+	if (!--worker->idle_rebind->cnt)
+		complete(&worker->idle_rebind->done);
+	spin_unlock_irq(&worker->pool->gcwq->lock);
 }
 
 /*
@@ -1339,8 +1349,16 @@ static void busy_worker_rebind_fn(struct work_struct *work)
 	struct worker *worker = container_of(work, struct worker, rebind_work);
 	struct global_cwq *gcwq = worker->pool->gcwq;
 
-	if (worker_maybe_bind_and_lock(worker))
-		worker_clr_flags(worker, WORKER_REBIND);
+	worker_maybe_bind_and_lock(worker);
+
+	/*
+	 * %WORKER_REBIND must be cleared even if the above binding failed;
+	 * otherwise, we may confuse the next CPU_UP cycle or oops / get
+	 * stuck by calling idle_worker_rebind() prematurely.  If CPU went
+	 * down again inbetween, %WORKER_UNBOUND would be set, so clearing
+	 * %WORKER_REBIND is always safe.
+	 */
+	worker_clr_flags(worker, WORKER_REBIND);
 
 	spin_unlock_irq(&gcwq->lock);
 }
@@ -1396,12 +1414,15 @@ retry:
 	/* set REBIND and kick idle ones, we'll wait for these later */
 	for_each_worker_pool(pool, gcwq) {
 		list_for_each_entry(worker, &pool->idle_list, entry) {
+			unsigned long worker_flags = worker->flags;
+
 			if (worker->flags & WORKER_REBIND)
 				continue;
 
-			/* morph UNBOUND to REBIND */
-			worker->flags &= ~WORKER_UNBOUND;
-			worker->flags |= WORKER_REBIND;
+			/* morph UNBOUND to REBIND atomically */
+			worker_flags &= ~WORKER_UNBOUND;
+			worker_flags |= WORKER_REBIND;
+			ACCESS_ONCE(worker->flags) = worker_flags;
 
 			idle_rebind.cnt++;
 			worker->idle_rebind = &idle_rebind;
@@ -1419,25 +1440,15 @@ retry:
 		goto retry;
 	}
 
-	/*
-	 * All idle workers are rebound and waiting for %WORKER_REBIND to
-	 * be cleared inside idle_worker_rebind().  Clear and release.
-	 * Clearing %WORKER_REBIND from this foreign context is safe
-	 * because these workers are still guaranteed to be idle.
-	 */
-	for_each_worker_pool(pool, gcwq)
-		list_for_each_entry(worker, &pool->idle_list, entry)
-			worker->flags &= ~WORKER_REBIND;
-
-	wake_up_all(&gcwq->rebind_hold);
-
-	/* rebind busy workers */
+	/* all idle workers are rebound, rebind busy workers */
 	for_each_busy_worker(worker, i, pos, gcwq) {
 		struct work_struct *rebind_work = &worker->rebind_work;
+		unsigned long worker_flags = worker->flags;
 
-		/* morph UNBOUND to REBIND */
-		worker->flags &= ~WORKER_UNBOUND;
-		worker->flags |= WORKER_REBIND;
+		/* morph UNBOUND to REBIND atomically */
+		worker_flags &= ~WORKER_UNBOUND;
+		worker_flags |= WORKER_REBIND;
+		ACCESS_ONCE(worker->flags) = worker_flags;
 
 		if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
 				     work_data_bits(rebind_work)))
@@ -1449,6 +1460,34 @@ retry:
 			    worker->scheduled.next,
 			    work_color_to_flags(WORK_NO_COLOR));
 	}
+
+	/*
+	 * All idle workers are rebound and waiting for %WORKER_REBIND to
+	 * be cleared inside idle_worker_rebind().  Clear and release.
+	 * Clearing %WORKER_REBIND from this foreign context is safe
+	 * because these workers are still guaranteed to be idle.
+	 *
+	 * We need to make sure all idle workers passed WORKER_REBIND wait
+	 * in idle_worker_rebind() before returning; otherwise, workers can
+	 * get stuck at the wait if hotplug cycle repeats.
+	 */
+	idle_rebind.cnt = 1;
+	INIT_COMPLETION(idle_rebind.done);
+
+	for_each_worker_pool(pool, gcwq) {
+		list_for_each_entry(worker, &pool->idle_list, entry) {
+			worker->flags &= ~WORKER_REBIND;
+			idle_rebind.cnt++;
+		}
+	}
+
+	wake_up_all(&gcwq->rebind_hold);
+
+	if (--idle_rebind.cnt) {
+		spin_unlock_irq(&gcwq->lock);
+		wait_for_completion(&idle_rebind.done);
+		spin_lock_irq(&gcwq->lock);
+	}
 }
 
 static struct worker *alloc_worker(void)
@@ -1794,9 +1833,45 @@ static bool manage_workers(struct worker *worker)
 	struct worker_pool *pool = worker->pool;
 	bool ret = false;
 
-	if (!mutex_trylock(&pool->manager_mutex))
+	if (pool->flags & POOL_MANAGING_WORKERS)
 		return ret;
 
+	pool->flags |= POOL_MANAGING_WORKERS;
+
+	/*
+	 * To simplify both worker management and CPU hotplug, hold off
+	 * management while hotplug is in progress.  CPU hotplug path can't
+	 * grab %POOL_MANAGING_WORKERS to achieve this because that can
+	 * lead to idle worker depletion (all become busy thinking someone
+	 * else is managing) which in turn can result in deadlock under
+	 * extreme circumstances.  Use @pool->manager_mutex to synchronize
+	 * manager against CPU hotplug.
+	 *
+	 * manager_mutex would always be free unless CPU hotplug is in
+	 * progress.  trylock first without dropping @gcwq->lock.
+	 */
+	if (unlikely(!mutex_trylock(&pool->manager_mutex))) {
+		spin_unlock_irq(&pool->gcwq->lock);
+		mutex_lock(&pool->manager_mutex);
+		/*
+		 * CPU hotplug could have happened while we were waiting
+		 * for manager_mutex.  Hotplug itself can't handle us
+		 * because manager isn't either on idle or busy list, and
+		 * @gcwq's state and ours could have deviated.
+		 *
+		 * As hotplug is now excluded via manager_mutex, we can
+		 * simply try to bind.  It will succeed or fail depending
+		 * on @gcwq's current state.  Try it and adjust
+		 * %WORKER_UNBOUND accordingly.
+		 */
+		if (worker_maybe_bind_and_lock(worker))
+			worker->flags &= ~WORKER_UNBOUND;
+		else
+			worker->flags |= WORKER_UNBOUND;
+
+		ret = true;
+	}
+
 	pool->flags &= ~POOL_MANAGE_WORKERS;
 
 	/*
@@ -1806,6 +1881,7 @@ static bool manage_workers(struct worker *worker)
 	ret |= maybe_destroy_workers(pool);
 	ret |= maybe_create_worker(pool);
 
+	pool->flags &= ~POOL_MANAGING_WORKERS;
 	mutex_unlock(&pool->manager_mutex);
 	return ret;
 }
@@ -3500,18 +3576,17 @@ static int __devinit workqueue_cpu_down_callback(struct notifier_block *nfb,
 #ifdef CONFIG_SMP
 
 struct work_for_cpu {
-	struct completion completion;
+	struct work_struct work;
 	long (*fn)(void *);
 	void *arg;
 	long ret;
 };
 
-static int do_work_for_cpu(void *_wfc)
+static void work_for_cpu_fn(struct work_struct *work)
 {
-	struct work_for_cpu *wfc = _wfc;
+	struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);
+
 	wfc->ret = wfc->fn(wfc->arg);
-	complete(&wfc->completion);
-	return 0;
 }
 
 /**
@@ -3526,19 +3601,11 @@ static int do_work_for_cpu(void *_wfc)
  */
 long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
 {
-	struct task_struct *sub_thread;
-	struct work_for_cpu wfc = {
-		.completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
-		.fn = fn,
-		.arg = arg,
-	};
+	struct work_for_cpu wfc = { .fn = fn, .arg = arg };
 
-	sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
-	if (IS_ERR(sub_thread))
-		return PTR_ERR(sub_thread);
-	kthread_bind(sub_thread, cpu);
-	wake_up_process(sub_thread);
-	wait_for_completion(&wfc.completion);
+	INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
+	schedule_work_on(cpu, &wfc.work);
+	flush_work(&wfc.work);
 	return wfc.ret;
 }
 EXPORT_SYMBOL_GPL(work_on_cpu);