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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: 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>

authored by

Szymon Wilczek and committed by
Konstantin Komarov
e37a75bb c6132696

+3 -2
+2
fs/ntfs3/frecord.c
··· 2107 2107 pages[i] = pg; 2108 2108 } 2109 2109 2110 + ni_lock(ni); 2110 2111 err = ni_read_frame(ni, frame_vbo, pages, pages_per_frame, 0); 2112 + ni_unlock(ni); 2111 2113 2112 2114 out1: 2113 2115 for (i = 0; i < pages_per_frame; i++) {
+1 -2
fs/ntfs3/inode.c
··· 748 748 } 749 749 750 750 if (is_compressed(ni)) { 751 - ni_lock(ni); 751 + /* ni_lock is taken inside ni_read_folio_cmpr after page locks */ 752 752 err = ni_read_folio_cmpr(ni, folio); 753 - ni_unlock(ni); 754 753 return err; 755 754 } 756 755