From e4545de5b035c7debb73d260c78377dbb69cbfb5 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Wed, 17 Jun 2015 12:49:23 +0100 Subject: [PATCH] Btrfs: fix fsync data loss after append write If we do an append write to a file (which increases its inode's i_size) that does not have the flag BTRFS_INODE_NEEDS_FULL_SYNC set in its inode, and the previous transaction added a new hard link to the file, which sets the flag BTRFS_INODE_COPY_EVERYTHING in the file's inode, and then fsync the file, the inode's new i_size isn't logged. This has the consequence that after the fsync log is replayed, the file size remains what it was before the append write operation, which means users/applications will not be able to read the data that was successsfully fsync'ed before. This happens because neither the inode item nor the delayed inode get their i_size updated when the append write is made - doing so would require starting a transaction in the buffered write path, something that we do not do intentionally for performance reasons. Fix this by making sure that when the flag BTRFS_INODE_COPY_EVERYTHING is set the inode is logged with its current i_size (log the in-memory inode into the log tree). This issue is not a recent regression and is easy to reproduce with the following test case for fstests: seq=`basename $0` seqres=$RESULT_DIR/$seq echo "QA output created by $seq" here=`pwd` tmp=/tmp/$$ status=1 # failure is the default! _cleanup() { _cleanup_flakey rm -f $tmp.* } trap "_cleanup; exit \$status" 0 1 2 3 15 # get standard environment, filters and checks . ./common/rc . ./common/filter . ./common/dmflakey # real QA test starts here _supported_fs generic _supported_os Linux _need_to_be_root _require_scratch _require_dm_flakey _require_metadata_journaling $SCRATCH_DEV _crash_and_mount() { # Simulate a crash/power loss. _load_flakey_table $FLAKEY_DROP_WRITES _unmount_flakey # Allow writes again and mount. This makes the fs replay its fsync log. _load_flakey_table $FLAKEY_ALLOW_WRITES _mount_flakey } rm -f $seqres.full _scratch_mkfs >> $seqres.full 2>&1 _init_flakey _mount_flakey # Create the test file with some initial data and then fsync it. # The fsync here is only needed to trigger the issue in btrfs, as it causes the # the flag BTRFS_INODE_NEEDS_FULL_SYNC to be removed from the btrfs inode. $XFS_IO_PROG -f -c "pwrite -S 0xaa 0 32k" \ -c "fsync" \ $SCRATCH_MNT/foo | _filter_xfs_io sync # Add a hard link to our file. # On btrfs this sets the flag BTRFS_INODE_COPY_EVERYTHING on the btrfs inode, # which is a necessary condition to trigger the issue. ln $SCRATCH_MNT/foo $SCRATCH_MNT/bar # Sync the filesystem to force a commit of the current btrfs transaction, this # is a necessary condition to trigger the bug on btrfs. sync # Now append more data to our file, increasing its size, and fsync the file. # In btrfs because the inode flag BTRFS_INODE_COPY_EVERYTHING was set and the # write path did not update the inode item in the btree nor the delayed inode # item (in memory struture) in the current transaction (created by the fsync # handler), the fsync did not record the inode's new i_size in the fsync # log/journal. This made the data unavailable after the fsync log/journal is # replayed. $XFS_IO_PROG -c "pwrite -S 0xbb 32K 32K" \ -c "fsync" \ $SCRATCH_MNT/foo | _filter_xfs_io echo "File content after fsync and before crash:" od -t x1 $SCRATCH_MNT/foo _crash_and_mount echo "File content after crash and log replay:" od -t x1 $SCRATCH_MNT/foo status=0 exit The expected file output before and after the crash/power failure expects the appended data to be available, which is: 0000000 aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa * 0100000 bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb * 0200000 Cc: stable@vger.kernel.org Signed-off-by: Filipe Manana Reviewed-by: Liu Bo Signed-off-by: Chris Mason --- fs/btrfs/tree-log.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 1ce80c1c4eb6..76c4f9d1b80a 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -4155,6 +4155,7 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans, u64 ino = btrfs_ino(inode); struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree; u64 logged_isize = 0; + bool need_log_inode_item = true; path = btrfs_alloc_path(); if (!path) @@ -4263,11 +4264,6 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans, } else { if (inode_only == LOG_INODE_ALL) fast_search = true; - ret = log_inode_item(trans, log, dst_path, inode); - if (ret) { - err = ret; - goto out_unlock; - } goto log_extents; } @@ -4290,6 +4286,9 @@ again: if (min_key.type > max_key.type) break; + if (min_key.type == BTRFS_INODE_ITEM_KEY) + need_log_inode_item = false; + src = path->nodes[0]; if (ins_nr && ins_start_slot + ins_nr == path->slots[0]) { ins_nr++; @@ -4360,6 +4359,11 @@ next_slot: log_extents: btrfs_release_path(path); btrfs_release_path(dst_path); + if (need_log_inode_item) { + err = log_inode_item(trans, log, dst_path, inode); + if (err) + goto out_unlock; + } if (fast_search) { /* * Some ordered extents started by fsync might have completed -- 2.20.1