[PATCH v6 16/17] btrfs: disable defrag on pre-content watched files

[Josef Bacik <josef@toxicpanda.com>]

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 <josef@toxicpanda.com>
---
 fs/btrfs/ioctl.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 226c91fe31a7..9b13df1ea729 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2638,6 +2638,15 @@ 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