[PATCH ] xfs: check for COW overflows in i_delayed_blks

Darrick J. Wong
2019-05-20T22:31:56Z

From: Darrick J. Wong <darrick.wong@oracle.com>

With the new copy on write functionality it's possible to reserve so
much COW space for a file that we end up overflowing i_delayed_blks.
The only user-visible effect of this is to cause totally wrong i_blocks
output in stat, so check for that.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
tests/xfs/907 | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++
tests/xfs/907.out | 8 ++
tests/xfs/group | 1
3 files changed, 189 insertions(+)
create mode 100755 tests/xfs/907
create mode 100644 tests/xfs/907.out

diff --git a/tests/xfs/907 b/tests/xfs/907
new file mode 100755
index 00000000..2c21ac8e
--- /dev/null
+++ b/tests/xfs/907
@@ -0,0 +1,180 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+# Copyright (c) 2019 Oracle, Inc. All Rights Reserved.
+#
+# FS QA Test No. 907
+#
+# Try to overflow i_delayed_blks by setting the largest cowextsize hint
+# possible, creating a sparse file with a single byte every cowextsize bytes,
+# reflinking it, and retouching every written byte to see if we can create
+# enough speculative COW reservations to overflow i_delayed_blks.
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1 # failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 7 15
+
+_cleanup()
+{
+ cd /
+ umount $loop_mount > /dev/null 2>&1
+ rm -rf $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/reflink
+. ./common/filter
+
+# real QA test starts here
+_supported_os Linux
+_supported_fs xfs
+_require_scratch_reflink
+_require_loop
+_require_xfs_debug # needed for xfs_bmap -c
+
+MAXEXTLEN=2097151 # cowextsize can't be more than MAXEXTLEN
+
+# Create a huge sparse filesystem on the scratch device because that's what
+# we're going to need to guarantee that we have enough blocks to overflow in
+# the first place. In the worst case we have a 64k-block filesystem in which
+# we have to be able to reserve 2^32 blocks. Adding in 20% overhead and a
+# 128M log, we get about 300T.
+echo "Format and mount"
+_scratch_mkfs > "$seqres.full" 2>&1
+_scratch_mount
+_require_fs_space $SCRATCH_MNT 200000 # 300T fs requires ~200MB of space
+
+loop_file=$SCRATCH_MNT/a.img
+loop_mount=$SCRATCH_MNT/a
+truncate -s 300T $loop_file
+loop_dev=$(_create_loop_device $loop_file)
+
+# Now we have to create the source file. The goal is to overflow a 32-bit
+# i_delayed_blks, which means that we have to create at least that many delayed
+# allocation block reservations. Take advantage of the fact that a cowextsize
+# hint causes creation of large speculative delalloc reservations in the cow
+# fork to reduce the amount of work we have to do.
+#
+# The maximum cowextsize is going to be MAXEXTLEN fs blocks on a 100T
+# filesystem, so start by setting up the hint. Note that the current fsxattr
+# interface specifies its u32 cowextsize hint in units of bytes and therefore
+# can't handle MAXEXTLEN * blksz on most filesystems, so we set it via mkfs
+# because mkfs takes units of fs blocks, not bytes.
+
+_mkfs_dev -d cowextsize=$MAXEXTLEN -l size=128m $loop_dev >> $seqres.full
+mkdir $loop_mount
+mount -t xfs $loop_dev $loop_mount
+
+echo "Create crazy huge file"
+huge_file="$loop_mount/a"
+touch "$huge_file"
+blksz=$(_get_file_block_size "$loop_mount")
+extsize_bytes="$(( MAXEXTLEN * blksz ))"
+
+# Make sure it actually set a hint.
+curr_cowextsize_str="$($XFS_IO_PROG -c 'cowextsize' "$huge_file")"
+echo "$curr_cowextsize_str" >> $seqres.full
+cowextsize_bytes="$(echo "$curr_cowextsize_str" | sed -e 's/^.\([0-9]*\).*$/\1/g')"
+test "$cowextsize_bytes" -eq 0 && echo "could not set cowextsize?"
+
+# Now we have to seed the file with sparse contents. Remember, the goal is to
+# create a little more than 2^32 delayed allocation blocks in the COW fork with
+# as little effort as possible. We know that speculative COW preallocation
+# will create MAXEXTLEN-length reservations for us, so that means we should
+# be able to get away with touching a single byte every extsize_bytes. We
+# do this backwards to avoid having to move EOF.
+nr="$(( ((2 ** 32) / MAXEXTLEN) + 100 ))"
+seq $nr -1 0 | while read n; do
+ off="$((n * extsize_bytes))"
+ $XFS_IO_PROG -c "pwrite $off 1" "$huge_file" > /dev/null
+done
+
+echo "Reflink crazy huge file"
+_cp_reflink "$huge_file" "$huge_file.b"
+
+# Now that we've shared all the blocks in the file, we touch them all again
+# to create speculative COW preallocations.
+echo "COW crazy huge file"
+seq $nr -1 0 | while read n; do
+ off="$((n * extsize_bytes))"
+ $XFS_IO_PROG -c "pwrite $off 1" "$huge_file" > /dev/null
+done
+
+# Compare the number of blocks allocated to this file (as reported by stat)
+# against the number of blocks that are in the COW fork. If either one is
+# less than 2^32 then we have evidence of an overflow problem.
+echo "Check crazy huge file"
+allocated_stat_blocks="$(stat -c %b "$huge_file")"
+stat_blksz="$(stat -c %B "$huge_file")"
+allocated_fsblocks=$(( allocated_stat_blocks * stat_blksz / blksz ))
+
+# Make sure we got enough COW reservations to overflow a 32-bit counter.
+
+# Return the number of delalloc & real blocks given bmap output for a fork of a
+# file. Output is in units of 512-byte blocks.
+count_fork_blocks() {
+ awk "
+{
+ if (\$3 == \"delalloc\") {
+ x += \$4;
+ } else if (\$3 == \"hole\") {
+ ;
+ } else {
+ x += \$6;
+ }
+}
+END {
+ print(x);
+}
+"
+}
+
+# Count the number of blocks allocated to a file based on the xfs_bmap output.
+# Output is in units of filesystem blocks.
+count_file_fork_blocks() {
+ local tag="$1"
+ local file="$2"
+ local args="$3"
+
+ $XFS_IO_PROG -c "bmap $args -l -p -v" "$huge_file" > $tmp.extents
+ echo "$tag fork map" >> $seqres.full
+ cat $tmp.extents >> $seqres.full
+ local sectors="$(count_fork_blocks < $tmp.extents)"
+ echo "$(( sectors / (blksz / 512) ))"
+}
+
+cowblocks=$(count_file_fork_blocks cow "$huge_file" "-c")
+attrblocks=$(count_file_fork_blocks attr "$huge_file" "-a")
+datablocks=$(count_file_fork_blocks data "$huge_file" "")
+
+# Did we create more than 2^32 blocks in the cow fork?
+echo "datablocks is $datablocks" >> $seqres.full
+echo "attrblocks is $attrblocks" >> $seqres.full
+echo "cowblocks is $cowblocks" >> $seqres.full
+test "$cowblocks" -lt $((2 ** 32)) && \
+ echo "cowblocks (${cowblocks}) should be more than 2^32!"
+
+# Does stat's block allocation count exceed 2^32?
+echo "stat blocks is $allocated_fsblocks" >> $seqres.full
+test "$allocated_fsblocks" -lt $((2 ** 32)) && \
+ echo "stat blocks (${allocated_fsblocks}) should be more than 2^32!"
+
+# Finally, does st_blocks match what we computed from the forks?
+expected_allocated_fsblocks=$((datablocks + cowblocks + attrblocks))
+echo "expected stat blocks is $expected_allocated_fsblocks" >> $seqres.full
+
+_within_tolerance "st_blocks" $allocated_fsblocks $expected_allocated_fsblocks 2% -v
+
+echo "Test done"
+_check_xfs_filesystem $loop_dev none none
+umount $loop_mount
+_destroy_loop_device $loop_dev
+
+# success, all done
+status=0
+exit
diff --git a/tests/xfs/907.out b/tests/xfs/907.out
new file mode 100644
index 00000000..cc07d659
--- /dev/null
+++ b/tests/xfs/907.out
@@ -0,0 +1,8 @@
+QA output created by 907
+Format and mount
+Create crazy huge file
+Reflink crazy huge file
+COW crazy huge file
+Check crazy huge file
+st_blocks is in range
+Test done
diff --git a/tests/xfs/group b/tests/xfs/group
index 5a4ef4bf..e0c7fc97 100644
--- a/tests/xfs/group
+++ b/tests/xfs/group
@@ -504,3 +504,4 @@
739 auto quick mkfs label
742 auto quick spaceman
743 auto quick health
+907 clone