From e37a75bb866c29da954b51d0dd7670406246d9ee Mon Sep 17 00:00:00 2001 From: Szymon Wilczek Date: Mon, 22 Dec 2025 16:10:10 +0100 Subject: [PATCH] fs/ntfs3: fix deadlock in ni_read_folio_cmpr 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 [almaz.alexandrovich@paragon-software.com: ni_readpage_cmpr was renamed to ni_read_folio_cmpr] Signed-off-by: Konstantin Komarov --- 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 03dcb66b5f6c..3025a404e695 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 ace9873adaae..4b50fdb4ff47 100644 --- a/fs/ntfs3/inode.c +++ b/fs/ntfs3/inode.c @@ -748,9 +748,8 @@ 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; } -- 2.47.3