Commit 4da2e26a authored Jan 06, 2016 by Zhao Lei Committed by David Sterba Feb 18, 2016

btrfs: Continue write in case of can_not_nocow



btrfs failed in xfstests btrfs/080 with -o nodatacow.

Can be reproduced by following script:
  DEV=/dev/vdg
  MNT=/mnt/tmp

  umount $DEV &>/dev/null
  mkfs.btrfs -f $DEV
  mount -o nodatacow $DEV $MNT

  dd if=/dev/zero of=$MNT/test bs=1 count=2048 &
  btrfs subvolume snapshot -r $MNT $MNT/test_snap &
  wait
  --
  We can see dd failed on NO_SPACE.

Reason:
  __btrfs_buffered_write should run cow write when no_cow impossible,
  and current code is designed with above logic.
  But check_can_nocow() have 2 type of return value(0 and <0) on
  can_not_no_cow, and current code only continue write on first case,
  the second case happened in doing subvolume.

Fix:
  Continue write when check_can_nocow() return 0 and <0.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>

parent 388f7b1d

fs/btrfs/file.c

+17 −20

Original line number	Diff line number	Diff line
		@@ -1525,12 +1525,9 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,

		reserve_bytes = num_pages << PAGE_CACHE_SHIFT;

		if (BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW \|
		BTRFS_INODE_PREALLOC)) {
		ret = check_can_nocow(inode, pos, &write_bytes);
		if (ret < 0)
		break;
		if (ret > 0) {
		if ((BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW \|
		BTRFS_INODE_PREALLOC)) &&
		check_can_nocow(inode, pos, &write_bytes) > 0) {
		/*
		* For nodata cow case, no need to reserve
		* data space.
		@@ -1545,7 +1542,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
		reserve_bytes = num_pages << PAGE_CACHE_SHIFT;
		goto reserve_metadata;
		}
		}

		ret = btrfs_check_data_free_space(inode, pos, write_bytes);
		if (ret < 0)
		break;