[PATCH 4.4 022/137] Btrfs: fix fitrim discarding device area reserved for boot loaders use

Greg Kroah-Hartman
2016-02-24T04:08:09Z

From: Filipe Manana <fdmanana@suse.com>

commit 8cdc7c5b00d945a3c823fc4277af304abb9cb43d upstream.

As of the 4.3 kernel release, the fitrim ioctl can now discard any region
of a disk that is not allocated to any chunk/block group, including the
first megabyte which is used for our primary superblock and by the boot
loader (grub for example).

Fix this by not allowing to trim/discard any region in the device starting
with an offset not greater than min(alloc_start_mount_option, 1Mb), just
as it was not possible before 4.3.

A reproducer test case for xfstests follows.

seq=`basename $0`
seqres=$RESULT_DIR/$seq
echo "QA output created by $seq"
tmp=/tmp/$$
status=1 # failure is the default!
trap "_cleanup; exit \$status" 0 1 2 3 15

_cleanup()
{
cd /
rm -f $tmp.*
}

# get standard environment, filters and checks
. ./common/rc
. ./common/filter

# real QA test starts here
_need_to_be_root
_supported_fs btrfs
_supported_os Linux
_require_scratch

rm -f $seqres.full

_scratch_mkfs >>$seqres.full 2>&1

# Write to the [0, 64Kb[ and [68Kb, 1Mb[ ranges of the device. These ranges are
# reserved for a boot loader to use (GRUB for example) and btrfs should never
# use them - neither for allocating metadata/data nor should trim/discard them.
# The range [64Kb, 68Kb[ is used for the primary superblock of the filesystem.
$XFS_IO_PROG -c "pwrite -S 0xfd 0 64K" $SCRATCH_DEV | _filter_xfs_io
$XFS_IO_PROG -c "pwrite -S 0xfd 68K 956K" $SCRATCH_DEV | _filter_xfs_io

# Now mount the filesystem and perform a fitrim against it.
_scratch_mount
_require_batched_discard $SCRATCH_MNT
$FSTRIM_PROG $SCRATCH_MNT

# Now unmount the filesystem and verify the content of the ranges was not
# modified (no trim/discard happened on them).
_scratch_unmount
echo "Content of the ranges [0, 64Kb] and [68Kb, 1Mb[ after fitrim:"
od -t x1 -N $((64 * 1024)) $SCRATCH_DEV
od -t x1 -j $((68 * 1024)) -N $((956 * 1024)) $SCRATCH_DEV

status=0
exit

Reported-by: Vincent Petry <PVince81@yahoo.fr>
Reported-by: Andrei Borzenkov <arvidjaar@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=109341
Fixes: 499f377f49f0 (btrfs: iterate over unused chunk space in FITRIM)
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/volumes.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1257,6 +1257,15 @@ int find_free_dev_extent_start(struct bt
int ret;
int slot;
struct extent_buffer *l;
+ u64 min_search_start;
+
+ /*
+ * We don't want to overwrite the superblock on the drive nor any area
+ * used by the boot loader (grub for example), so we make sure to start
+ * at an offset of at least 1MB.
+ */
+ min_search_start = max(root->fs_info->alloc_start, 1024ull * 1024);
+ search_start = max(search_start, min_search_start);

path = btrfs_alloc_path();
if (!path)
@@ -1397,18 +1406,9 @@ int find_free_dev_extent(struct btrfs_tr
struct btrfs_device *device, u64 num_bytes,
u64 *start, u64 *len)
{
- struct btrfs_root *root = device->dev_root;
- u64 search_start;
-
/* FIXME use last free of some kind */
-
- /*
- * we don't want to overwrite the superblock on the drive,
- * so we make sure to start at an offset of at least 1MB
- */
- search_start = max(root->fs_info->alloc_start, 1024ull * 1024);
return find_free_dev_extent_start(trans->transaction, device,
- num_bytes, search_start, start, len);
+ num_bytes, 0, start, len);
}

static int btrfs_free_dev_extent(struct btrfs_trans_handle *trans,