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btrfs: Continue write in case of can_not_nocow

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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>
This commit is contained in:
Zhao Lei 2016-01-06 18:24:43 +08:00 committed by David Sterba
parent 388f7b1d6e
commit 4da2e26a2a
1 changed files with 17 additions and 20 deletions
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37
fs/btrfs/file.c
View file

@ -1525,27 +1525,24 @@ 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) {
/*
* For nodata cow case, no need to reserve
* data space.
*/
only_release_metadata = true;
/*
* our prealloc extent may be smaller than
* write_bytes, so scale down.
*/
num_pages = DIV_ROUND_UP(write_bytes + offset,
PAGE_CACHE_SIZE);
reserve_bytes = num_pages << PAGE_CACHE_SHIFT;
goto reserve_metadata;
}
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.
*/
only_release_metadata = true;
/*
* our prealloc extent may be smaller than
* write_bytes, so scale down.
*/
num_pages = DIV_ROUND_UP(write_bytes + offset,
PAGE_CACHE_SIZE);
reserve_bytes = num_pages << PAGE_CACHE_SHIFT;
goto reserve_metadata;
}
ret = btrfs_check_data_free_space(inode, pos, write_bytes);
if (ret < 0)
break;