From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	syzbot+5af33dd272b913b65880@syzkaller.appspotmail.com,
	Szymon Wilczek <swilczek.lx@gmail.com>,
	Konstantin Komarov <almaz.alexandrovich@paragon-software.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.19 618/781] fs/ntfs3: fix deadlock in ni_read_folio_cmpr
Date: Tue, 24 Feb 2026 17:22:07 -0800
Message-ID: <20260225012414.963371941@linuxfoundation.org>
In-Reply-To: <20260225012359.695468795@linuxfoundation.org>
References: <20260225012359.695468795@linuxfoundation.org>
User-Agent: quilt/0.69
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

6.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Szymon Wilczek <swilczek.lx@gmail.com>

[ Upstream commit e37a75bb866c29da954b51d0dd7670406246d9ee ]

Syzbot reported a task hung in ni_readpage_cmpr (now ni_read_folio_cmpr).
This is caused by a lock inversion deadlock involving the inode mutex
(ni_lock) and page locks.

Scenario:
1. Task A enters ntfs_read_folio() for page X. It acquires ni_lock.
2. Task A calls ni_read_folio_cmpr(), which attempts to lock all pages in
   the compressed frame (including page Y).
3. Concurrently, Task B (e.g., via readahead) has locked page Y and
   calls ntfs_read_folio().
4. Task B waits for ni_lock (held by A).
5. Task A waits for page Y lock (held by B).
   -> DEADLOCK.

The fix is to restructure locking: do not take ni_lock in ntfs_read_folio().
Instead, acquire ni_lock inside ni_read_folio_cmpr() ONLY AFTER all required
page locks for the frame have been successfully acquired. This restores the
correct lock ordering (Page Lock -> ni_lock) consistent with VFS.

Reported-by: syzbot+5af33dd272b913b65880@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5af33dd272b913b65880
Fixes: f35590ee26f5 ("fs/ntfs3: remove ntfs_bio_pages and use page cache for compressed I/O")
Signed-off-by: Szymon Wilczek <swilczek.lx@gmail.com>
[almaz.alexandrovich@paragon-software.com: ni_readpage_cmpr was renamed to ni_read_folio_cmpr]
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ntfs3/frecord.c | 2 ++
 fs/ntfs3/inode.c   | 3 +--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
index 7e3d61de2f8fa..d5bbd47e1ee9d 100644
--- a/fs/ntfs3/frecord.c
+++ b/fs/ntfs3/frecord.c
@@ -2107,7 +2107,9 @@ int ni_read_folio_cmpr(struct ntfs_inode *ni, struct folio *folio)
 		pages[i] = pg;
 	}
 
+	ni_lock(ni);
 	err = ni_read_frame(ni, frame_vbo, pages, pages_per_frame, 0);
+	ni_unlock(ni);
 
 out1:
 	for (i = 0; i < pages_per_frame; i++) {
diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index 1319b99dfeb41..ec8e954f4426c 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -735,9 +735,8 @@ static int ntfs_read_folio(struct file *file, struct folio *folio)
 	}
 
 	if (is_compressed(ni)) {
-		ni_lock(ni);
+		/* ni_lock is taken inside ni_read_folio_cmpr after page locks */
 		err = ni_read_folio_cmpr(ni, folio);
-		ni_unlock(ni);
 		return err;
 	}
 
-- 
2.51.0