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btrfs: qgroup: Prevent qgroup->reserved from going subzero

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While free'ing qgroup->reserved resources, we much check if
the page has not been invalidated by a truncate operation
by checking if the page is still dirty before reducing the
qgroup resources. Resources in such a case are free'd when
the entire extent is released by delayed_ref.

This fixes a double accounting while releasing resources
in case of truncating a file, reproduced by the following testcase.

SCRATCH_DEV=/dev/vdb
SCRATCH_MNT=/mnt
mkfs.btrfs -f $SCRATCH_DEV
mount -t btrfs $SCRATCH_DEV $SCRATCH_MNT
cd $SCRATCH_MNT
btrfs quota enable $SCRATCH_MNT
btrfs subvolume create a
btrfs qgroup limit 500m a $SCRATCH_MNT
sync
for c in {1..15}; do
dd if=/dev/zero  bs=1M count=40 of=$SCRATCH_MNT/a/file;
done

sleep 10
sync
sleep 5

touch $SCRATCH_MNT/a/newfile

echo "Removing file"
rm $SCRATCH_MNT/a/file

Fixes: b9d0b38928 ("btrfs: Add handler for invalidate page")
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Goldwyn Rodrigues 2016-09-30 10:40:52 -05:00 committed by David Sterba
parent 4547f4d8ff
commit 0b34c261e2
1 changed files with 7 additions and 2 deletions
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9
fs/btrfs/inode.c
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@ -8930,9 +8930,14 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset,
* So even we call qgroup_free_data(), it won't decrease reserved
* space.
* 2) Not written to disk
* This means the reserved space should be freed here.
* This means the reserved space should be freed here. However,
* if a truncate invalidates the page (by clearing PageDirty)
* and the page is accounted for while allocating extent
* in btrfs_check_data_free_space() we let delayed_ref to
* free the entire extent.
*/
btrfs_qgroup_free_data(inode, page_start, PAGE_SIZE);
if (PageDirty(page))
btrfs_qgroup_free_data(inode, page_start, PAGE_SIZE);
if (!inode_evicting) {
clear_extent_bit(tree, page_start, page_end,
EXTENT_LOCKED | EXTENT_DIRTY |