linux-ext4 - [PATCH 17/19] btrfs: disable defrag on pre-content watched files

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Message-Id: <20241121112218.8249-18-jack@suse.cz>
Date: Thu, 21 Nov 2024 12:22:16 +0100
From: Jan Kara <jack@...e.cz>
To: <linux-fsdevel@...r.kernel.org>
Cc: Amir Goldstein <amir73il@...il.com>,
	Josef Bacik <josef@...icpanda.com>,
	brauner@...nel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	linux-xfs@...r.kernel.org,
	linux-btrfs@...r.kernel.org,
	linux-ext4@...r.kernel.org,
	linux-mm@...ck.org,
	Jan Kara <jack@...e.cz>
Subject: [PATCH 17/19] btrfs: disable defrag on pre-content watched files

From: Josef Bacik <josef@...icpanda.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@...icpanda.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Link: https://patch.msgid.link/4cc5bcea13db7904174353d08e85157356282a59.1731684329.git.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..a908f75458f0 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 (unlikely(FMODE_FSNOTIFY_HSM(file->f_mode))) {
+			ret = -EINVAL;
+			goto out;
+		}
+
 		if (argp) {
 			if (copy_from_user(&range, argp, sizeof(range))) {
 				ret = -EFAULT;
-- 
2.35.3