Merge tag 'drm-intel-next-2015-03-13-merge' of git://anongit.freedesktop.org/drm-intel into drm-next

drm-intel-next-2015-03-13-rebased:
- EU count report param for gen9+ (Jeff McGee)
- piles of pll/wm/... fixes for chv, finally out of preliminary hw support
  (Ville, Vijay)
- gen9 rps support from Akash
- more work to move towards atomic from Matt, Ander and others
- runtime pm support for skl (Damien)
- edp1.4 intermediate link clock support (Sonika)
- use frontbuffer tracking for fbc (Paulo)
- remove ilk rc6 (John Harrison)
- a bunch of smaller things and fixes all over

Includes backmerge because git rerere couldn't keep up any more.

* tag 'drm-intel-next-2015-03-13-merge' of git://anongit.freedesktop.org/drm-intel: (366 commits)
  drm/i915: Make sure the primary plane is enabled before reading out the fb state
  drm/i915: Update DRIVER_DATE to 20150313
  drm/i915: Fix vmap_batch page iterator overrun
  drm/i915: Export total subslice and EU counts
  drm/i915: redefine WARN_ON_ONCE to include the condition
  drm/i915/skl: Implement WaDisableHBR2
  drm/i915: Remove the preliminary_hw_support shackles from CHV
  drm/i915: Read CHV_PLL_DW8 from the correct offset
  drm/i915: Rewrite IVB FDI bifurcation conflict checks
  drm/i915: Rewrite some some of the FDI lane checks
  drm/i915/skl: Enable the RPS interrupts programming
  drm/i915/skl: Enabling processing of Turbo interrupts
  drm/i915/skl: Updated the i915_frequency_info debugfs function
  drm/i915: Simplify the way BC bifurcation state consistency is kept
  drm/i915/skl: Updated the act_freq_mhz_show sysfs function
  drm/i915/skl: Updated the gen9_enable_rps function
  drm/i915/skl: Updated the gen6_rps_limits function
  drm/i915/skl: Restructured the gen6_set_rps_thresholds function
  drm/i915/skl: Updated the gen6_set_rps function
  drm/i915/skl: Updated the gen6_init_rps_frequencies function
  ...

1 files changed, 52 insertions, 4 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f28849394791..41ff75b478c6 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2728,19 +2728,57 @@ bool flush_work(struct work_struct *work)
 }
 EXPORT_SYMBOL_GPL(flush_work);
 
+struct cwt_wait {
+	wait_queue_t		wait;
+	struct work_struct	*work;
+};
+
+static int cwt_wakefn(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+	struct cwt_wait *cwait = container_of(wait, struct cwt_wait, wait);
+
+	if (cwait->work != key)
+		return 0;
+	return autoremove_wake_function(wait, mode, sync, key);
+}
+
 static bool __cancel_work_timer(struct work_struct *work, bool is_dwork)
 {
+	static DECLARE_WAIT_QUEUE_HEAD(cancel_waitq);
 	unsigned long flags;
 	int ret;
 
 	do {
 		ret = try_to_grab_pending(work, is_dwork, &flags);
 		/*
-		 * If someone else is canceling, wait for the same event it
-		 * would be waiting for before retrying.
+		 * If someone else is already canceling, wait for it to
+		 * finish.  flush_work() doesn't work for PREEMPT_NONE
+		 * because we may get scheduled between @work's completion
+		 * and the other canceling task resuming and clearing
+		 * CANCELING - flush_work() will return false immediately
+		 * as @work is no longer busy, try_to_grab_pending() will
+		 * return -ENOENT as @work is still being canceled and the
+		 * other canceling task won't be able to clear CANCELING as
+		 * we're hogging the CPU.
+		 *
+		 * Let's wait for completion using a waitqueue.  As this
+		 * may lead to the thundering herd problem, use a custom
+		 * wake function which matches @work along with exclusive
+		 * wait and wakeup.
 		 */
-		if (unlikely(ret == -ENOENT))
-			flush_work(work);
+		if (unlikely(ret == -ENOENT)) {
+			struct cwt_wait cwait;
+
+			init_wait(&cwait.wait);
+			cwait.wait.func = cwt_wakefn;
+			cwait.work = work;
+
+			prepare_to_wait_exclusive(&cancel_waitq, &cwait.wait,
+						  TASK_UNINTERRUPTIBLE);
+			if (work_is_canceling(work))
+				schedule();
+			finish_wait(&cancel_waitq, &cwait.wait);
+		}
 	} while (unlikely(ret < 0));
 
 	/* tell other tasks trying to grab @work to back off */
@@ -2749,6 +2787,16 @@ static bool __cancel_work_timer(struct work_struct *work, bool is_dwork)
 
 	flush_work(work);
 	clear_work_data(work);
+
+	/*
+	 * Paired with prepare_to_wait() above so that either
+	 * waitqueue_active() is visible here or !work_is_canceling() is
+	 * visible there.
+	 */
+	smp_mb();
+	if (waitqueue_active(&cancel_waitq))
+		__wake_up(&cancel_waitq, TASK_NORMAL, 1, work);
+
 	return ret;
 }