Merge commit 'v3.2-rc3' into stable/for-linus-3.3

* commit 'v3.2-rc3': (412 commits)
  Linux 3.2-rc3
  virtio-pci: make reset operation safer
  virtio-mmio: Correct the name of the guest features selector
  virtio: add HAS_IOMEM dependency to MMIO platform bus driver
  eCryptfs: Extend array bounds for all filename chars
  eCryptfs: Flush file in vma close
  eCryptfs: Prevent file create race condition
  regulator: TPS65910: Fix VDD1/2 voltage selector count
  i2c: Make i2cdev_notifier_call static
  i2c: Delete ANY_I2C_BUS
  i2c: Fix device name for 10-bit slave address
  i2c-algo-bit: Generate correct i2c address sequence for 10-bit target
  drm: integer overflow in drm_mode_dirtyfb_ioctl()
  Revert "of/irq: of_irq_find_parent: check for parent equal to child"
  drivers/gpu/vga/vgaarb.c: add missing kfree
  drm/radeon/kms/atom: unify i2c gpio table handling
  drm/radeon/kms: fix up gpio i2c mask bits for r4xx for real
  ttm: Don't return the bo reserved on error path
  mount_subtree() pointless use-after-free
  iio: fix a leak due to improper use of anon_inode_getfd()
  ...

1 files changed, 16 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 0fe615e4ea3..dede441bdee 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -514,10 +514,25 @@ static inline int should_cow_block(struct btrfs_trans_handle *trans,
 				   struct btrfs_root *root,
 				   struct extent_buffer *buf)
 {
+	/* ensure we can see the force_cow */
+	smp_rmb();
+
+	/*
+	 * We do not need to cow a block if
+	 * 1) this block is not created or changed in this transaction;
+	 * 2) this block does not belong to TREE_RELOC tree;
+	 * 3) the root is not forced COW.
+	 *
+	 * What is forced COW:
+	 *    when we create snapshot during commiting the transaction,
+	 *    after we've finished coping src root, we must COW the shared
+	 *    block to ensure the metadata consistency.
+	 */
 	if (btrfs_header_generation(buf) == trans->transid &&
 	    !btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN) &&
 	    !(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID &&
-	      btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)))
+	      btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)) &&
+	    !root->force_cow)
 		return 0;
 	return 1;
 }