Merge commit 'v3.6-rc1' into linux-next

* commit 'v3.6-rc1': (9532 commits)
  Linux 3.6-rc1
  mm: remove node_start_pfn checking in new WARN_ON for now
  ARM: mmp: add missing irqs.h
  arm: mvebu: fix typo in .dtsi comment for Armada XP SoCs
  ARM: PRIMA2: delete redundant codes to restore LATCHED when timer resumes
  libceph: fix crypto key null deref, memory leak
  ceph: simplify+fix atomic_open
  sh: explicitly include sh_dma.h in setup-sh7722.c
  um: Add arch/x86/um to MAINTAINERS
  um: pass siginfo to guest process
  um: fix ubd_file_size for read-only files
  md/dm-raid: DM_RAID should select MD_RAID10
  md/raid1: submit IO from originating thread instead of md thread.
  raid5: raid5d handle stripe in batch way
  raid5: make_request use batch stripe release
  um: pull interrupt_end() into userspace()
  um: split syscall_trace(), pass pt_regs to it
  um: switch UPT_SET_RETURN_VALUE and regs_return_value to pt_regs
  MIPS: Loongson 2: Sort out clock managment.
  locks: remove unused lm_release_private
  ...

1 files changed, 9 insertions, 5 deletions

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 272f911203ff..a44eff074805 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -78,13 +78,15 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
 		write_lock(&eb->lock);
 		WARN_ON(atomic_read(&eb->spinning_writers));
 		atomic_inc(&eb->spinning_writers);
-		if (atomic_dec_and_test(&eb->blocking_writers))
+		if (atomic_dec_and_test(&eb->blocking_writers) &&
+		    waitqueue_active(&eb->write_lock_wq))
 			wake_up(&eb->write_lock_wq);
 	} else if (rw == BTRFS_READ_LOCK_BLOCKING) {
 		BUG_ON(atomic_read(&eb->blocking_readers) == 0);
 		read_lock(&eb->lock);
 		atomic_inc(&eb->spinning_readers);
-		if (atomic_dec_and_test(&eb->blocking_readers))
+		if (atomic_dec_and_test(&eb->blocking_readers) &&
+		    waitqueue_active(&eb->read_lock_wq))
 			wake_up(&eb->read_lock_wq);
 	}
 	return;
@@ -199,7 +201,8 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
 	}
 	btrfs_assert_tree_read_locked(eb);
 	WARN_ON(atomic_read(&eb->blocking_readers) == 0);
-	if (atomic_dec_and_test(&eb->blocking_readers))
+	if (atomic_dec_and_test(&eb->blocking_readers) &&
+	    waitqueue_active(&eb->read_lock_wq))
 		wake_up(&eb->read_lock_wq);
 	atomic_dec(&eb->read_locks);
 }
@@ -247,8 +250,9 @@ void btrfs_tree_unlock(struct extent_buffer *eb)
 	if (blockers) {
 		WARN_ON(atomic_read(&eb->spinning_writers));
 		atomic_dec(&eb->blocking_writers);
-		smp_wmb();
-		wake_up(&eb->write_lock_wq);
+		smp_mb();
+		if (waitqueue_active(&eb->write_lock_wq))
+			wake_up(&eb->write_lock_wq);
 	} else {
 		WARN_ON(atomic_read(&eb->spinning_writers) != 1);
 		atomic_dec(&eb->spinning_writers);