On Wed, 6 Jan 2016 19:00:17 +0800 Zhao Lei <zhao...@cn.fujitsu.com> wrote:
> 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. > > Signed-off-by: Zhao Lei <zhao...@cn.fujitsu.com> Guys please don't forget about this patch. It solves real problem for people, http://www.spinics.net/lists/linux-btrfs/msg51276.html http://www.spinics.net/lists/linux-btrfs/msg51819.html but it's not in 4.4.1, not in 4.4.2... and now not in 4.4.3 > --- > fs/btrfs/file.c | 37 +++++++++++++++++-------------------- > 1 file changed, 17 insertions(+), 20 deletions(-) > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > index 977e715..11fd981 100644 > --- a/fs/btrfs/file.c > +++ b/fs/btrfs/file.c > @@ -1516,27 +1516,24 @@ 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; -- With respect, Roman
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