We queue up inodes to be defrag'ed asynchronously, which means we do not have their original file for readahead. This means that the code to skip readahead on pre-content watched files will not run, and we could potentially read in empty pages.
Handle this corner case by disabling defrag on files that are currently being watched for pre-content events. Signed-off-by: Josef Bacik <[email protected]> --- fs/btrfs/ioctl.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index e0a664b8a46a..529f7416814f 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -2640,6 +2640,15 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp) goto out; } + /* + * Don't allow defrag on pre-content watched files, as it could + * populate the page cache with 0's via readahead. + */ + if (fsnotify_file_has_pre_content_watches(file)) { + ret = -EINVAL; + goto out; + } + if (argp) { if (copy_from_user(&range, argp, sizeof(range))) { ret = -EFAULT; -- 2.43.0
