[PATCH 4.4 37/38] btrfs: qgroup: Prevent qgroup->reserved from going subzero

From: Greg Kroah-Hartman
Date: Thu Nov 17 2016 - 05:40:34 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>

commit 0b34c261e235a5c74dcf78bd305845bd15fe2b42 upstream.

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.

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

sleep 10
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@xxxxxxxx>
Reviewed-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/btrfs/inode.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8691,9 +8691,14 @@ static void btrfs_invalidatepage(struct
* 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_CACHE_SIZE);
+ if (PageDirty(page))
+ btrfs_qgroup_free_data(inode, page_start, PAGE_SIZE);
if (!inode_evicting) {
clear_extent_bit(tree, page_start, page_end,