On Wed, Sep 4, 2024 at 10:29 PM Josef Bacik <[email protected]> wrote: > > 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.
IIUC, you are disabling the *start* of async defrag. What happens if defrag has already started and then a pre-content watch is set up? Do we care about this corner of a corner case? Thanks, Amir. > > 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 >
