Unverified Commit e37a75bb authored by Szymon Wilczek's avatar Szymon Wilczek Committed by Konstantin Komarov
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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: default avatar <syzbot+5af33dd272b913b65880@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=5af33dd272b913b65880


Fixes: f35590ee ("fs/ntfs3: remove ntfs_bio_pages and use page cache for compressed I/O")
Signed-off-by: default avatarSzymon Wilczek <swilczek.lx@gmail.com>
[almaz.alexandrovich@paragon-software.com: ni_readpage_cmpr was renamed to ni_read_folio_cmpr]
Signed-off-by: default avatarKonstantin Komarov <almaz.alexandrovich@paragon-software.com>
parent c6132696

fs/ntfs3/frecord.c

+2 −0
Original line number Diff line number Diff line
@@ -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++) {

fs/ntfs3/inode.c

+1 −2
Original line number Diff line number Diff line
@@ -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;

	}