btrfs: disable defrag on pre-content watched files

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>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/4cc5bcea13db7904174353d08e85157356282a59.1731684329.git.josef@toxicpanda.com

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index c9302d1931870dca5916ac66b218eeb28a4357ff..51b439537049c833fed59d77b3b26641cfde2f9b 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2635,6 +2635,15 @@ 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 (unlikely(FMODE_FSNOTIFY_HSM(file->f_mode))) {
+                       ret = -EINVAL;
+                       goto out;
+               }
+
                if (argp) {
                        if (copy_from_user(&range, argp, sizeof(range))) {
                                ret = -EFAULT;