From: Filipe Manana fdmanana@suse.com
commit 95418ed1d10774cd9a49af6f39e216c1256f1eeb upstream.
When doing a fast fsync for a range that starts at an offset greater than zero, we can end up with a log that when replayed causes the respective inode miss a file extent item representing a hole if we are not using the NO_HOLES feature. This is because for fast fsyncs we don't log any extents that cover a range different from the one requested in the fsync.
Example scenario to trigger it:
$ mkfs.btrfs -O ^no-holes -f /dev/sdd $ mount /dev/sdd /mnt
# Create a file with a single 256K and fsync it to clear to full sync # bit in the inode - we want the msync below to trigger a fast fsync. $ xfs_io -f -c "pwrite -S 0xab 0 256K" -c "fsync" /mnt/foo
# Force a transaction commit and wipe out the log tree. $ sync
# Dirty 768K of data, increasing the file size to 1Mb, and flush only # the range from 256K to 512K without updating the log tree # (sync_file_range() does not trigger fsync, it only starts writeback # and waits for it to finish).
$ xfs_io -c "pwrite -S 0xcd 256K 768K" /mnt/foo $ xfs_io -c "sync_range -abw 256K 256K" /mnt/foo
# Now dirty the range from 768K to 1M again and sync that range. $ xfs_io -c "mmap -w 768K 256K" \ -c "mwrite -S 0xef 768K 256K" \ -c "msync -s 768K 256K" \ -c "munmap" \ /mnt/foo
<power fail>
# Mount to replay the log. $ mount /dev/sdd /mnt $ umount /mnt
$ btrfs check /dev/sdd Opening filesystem to check... Checking filesystem on /dev/sdd UUID: 482fb574-b288-478e-a190-a9c44a78fca6 [1/7] checking root items [2/7] checking extents [3/7] checking free space cache [4/7] checking fs roots root 5 inode 257 errors 100, file extent discount Found file extent holes: start: 262144, len: 524288 ERROR: errors found in fs roots found 720896 bytes used, error(s) found total csum bytes: 512 total tree bytes: 131072 total fs tree bytes: 32768 total extent tree bytes: 16384 btree space waste bytes: 123514 file data blocks allocated: 589824 referenced 589824
Fix this issue by setting the range to full (0 to LLONG_MAX) when the NO_HOLES feature is not enabled. This results in extra work being done but it gives the guarantee we don't end up with missing holes after replaying the log.
CC: stable@vger.kernel.org # 4.19+ Reviewed-by: Josef Bacik josef@toxicpanda.com Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/file.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -2072,6 +2072,16 @@ int btrfs_sync_file(struct file *file, l btrfs_init_log_ctx(&ctx, inode);
/* + * Set the range to full if the NO_HOLES feature is not enabled. + * This is to avoid missing file extent items representing holes after + * replaying the log. + */ + if (!btrfs_fs_incompat(fs_info, NO_HOLES)) { + start = 0; + end = LLONG_MAX; + } + + /* * We write the dirty pages in the range and wait until they complete * out of the ->i_mutex. If so, we can flush the dirty pages by * multi-task, and make the performance up. See