Merge branches 'clockevents/4.4-fixes' and 'clockevents/4.5-fixes' of http://git.linaro.org/people/daniel.lezcano/linux into timers/urgent

Pull in fixes from Daniel Lezcano:

 - Fix the vt8500 timer leading to a system lock up when dealing with too
   small delta (Roman Volkov)

 - Select the CLKSRC_MMIO when the fsl_ftm_timer is enabled with COMPILE_TEST
   (Daniel Lezcano)

 - Prevent to compile timers using the 'iomem' API when the architecture has
   not HAS_IOMEM set (Richard Weinberger)

1 files changed, 16 insertions, 3 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 8ed2ffd963c5..7340353f8aea 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -957,8 +957,9 @@ EXPORT_SYMBOL(congestion_wait);
  * jiffies for either a BDI to exit congestion of the given @sync queue
  * or a write to complete.
  *
- * In the absence of zone congestion, cond_resched() is called to yield
- * the processor if necessary but otherwise does not sleep.
+ * In the absence of zone congestion, a short sleep or a cond_resched is
+ * performed to yield the processor and to allow other subsystems to make
+ * a forward progress.
  *
  * The return value is 0 if the sleep is for the full timeout. Otherwise,
  * it is the number of jiffies that were still remaining when the function
@@ -978,7 +979,19 @@ long wait_iff_congested(struct zone *zone, int sync, long timeout)
          */
         if (atomic_read(&nr_wb_congested[sync]) == 0 ||
             !test_bit(ZONE_CONGESTED, &zone->flags)) {
-                cond_resched();
+
+                /*
+                 * Memory allocation/reclaim might be called from a WQ
+                 * context and the current implementation of the WQ
+                 * concurrency control doesn't recognize that a particular
+                 * WQ is congested if the worker thread is looping without
+                 * ever sleeping. Therefore we have to do a short sleep
+                 * here rather than calling cond_resched().
+                 */
+                if (current->flags & PF_WQ_WORKER)
+                        schedule_timeout(1);
+                else
+                        cond_resched();
 
                 /* In case we scheduled, work out time remaining */
                 ret = timeout - (jiffies - start);