Merge commit 'c104f1fa1ecf4ee0fc06e31b1f77630b2551be81' into stable/for-linus-3.4

* commit 'c104f1fa1ecf4ee0fc06e31b1f77630b2551be81': (14566 commits)
  cpufreq: OMAP: fix build errors: depends on ARCH_OMAP2PLUS
  sparc64: Eliminate obsolete __handle_softirq() function
  sparc64: Fix bootup crash on sun4v.
  kconfig: delete last traces of __enabled_ from autoconf.h
  Revert "kconfig: fix __enabled_ macros definition for invisible and un-selected symbols"
  kconfig: fix IS_ENABLED to not require all options to be defined
  irq_domain: fix type mismatch in debugfs output format
  staging: android: fix mem leaks in __persistent_ram_init()
  staging: vt6656: Don't leak memory in drivers/staging/vt6656/ioctl.c::private_ioctl()
  staging: iio: hmc5843: Fix crash in probe function.
  panic: fix stack dump print on direct call to panic()
  drivers/rtc/rtc-pl031.c: enable clock on all ST variants
  Revert "mm: vmscan: fix misused nr_reclaimed in shrink_mem_cgroup_zone()"
  hugetlb: fix race condition in hugetlb_fault()
  drivers/rtc/rtc-twl.c: use static register while reading time
  drivers/rtc/rtc-s3c.c: add placeholder for driver private data
  drivers/rtc/rtc-s3c.c: fix compilation error
  MAINTAINERS: add PCDP console maintainer
  memcg: do not open code accesses to res_counter members
  drivers/rtc/rtc-efi.c: fix section mismatch warning
  ...

1 files changed, 18 insertions, 5 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7ba8feae11b8..dd8e2aafb07e 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -318,7 +318,7 @@ static void wakeup_timer_fn(unsigned long data)
         if (bdi->wb.task) {
                 trace_writeback_wake_thread(bdi);
                 wake_up_process(bdi->wb.task);
-        } else {
+        } else if (bdi->dev) {
                 /*
                  * When bdi tasks are inactive for long time, they are killed.
                  * In this case we have to wake-up the forker thread which
@@ -584,6 +584,8 @@ EXPORT_SYMBOL(bdi_register_dev);
  */
 static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 {
+        struct task_struct *task;
+
         if (!bdi_cap_writeback_dirty(bdi))
                 return;
 
@@ -602,8 +604,13 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
          * Finally, kill the kernel thread. We don't need to be RCU
          * safe anymore, since the bdi is gone from visibility.
          */
-        if (bdi->wb.task)
-                kthread_stop(bdi->wb.task);
+        spin_lock_bh(&bdi->wb_lock);
+        task = bdi->wb.task;
+        bdi->wb.task = NULL;
+        spin_unlock_bh(&bdi->wb_lock);
+
+        if (task)
+                kthread_stop(task);
 }
 
 /*
@@ -623,7 +630,9 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
 
 void bdi_unregister(struct backing_dev_info *bdi)
 {
-        if (bdi->dev) {
+        struct device *dev = bdi->dev;
+
+        if (dev) {
                 bdi_set_min_ratio(bdi, 0);
                 trace_writeback_bdi_unregister(bdi);
                 bdi_prune_sb(bdi);
@@ -632,8 +641,12 @@ void bdi_unregister(struct backing_dev_info *bdi)
                 if (!bdi_cap_flush_forker(bdi))
                         bdi_wb_shutdown(bdi);
                 bdi_debug_unregister(bdi);
-                device_unregister(bdi->dev);
+
+                spin_lock_bh(&bdi->wb_lock);
                 bdi->dev = NULL;
+                spin_unlock_bh(&bdi->wb_lock);
+
+                device_unregister(dev);
         }
 }
 EXPORT_SYMBOL(bdi_unregister);