fs/ntfs3: don't hold ni_lock when calling truncate_setsize()

syzbot is reporting hung task at do_user_addr_fault() [1], for there is
a silent deadlock between PG_locked bit and ni_lock lock.

Since filemap_update_page() calls filemap_read_folio() after calling
folio_trylock() which will set PG_locked bit, ntfs_truncate() must not
call truncate_setsize() which will wait for PG_locked bit to be cleared
when holding ni_lock lock.

Link: https://lore.kernel.org/all/[email protected]/
Link: https://syzkaller.appspot.com/bug?extid=bed15dbf10294aa4f2ae [1]
Reported-by: syzbot <[email protected]>
Debugged-by: Linus Torvalds <[email protected]>
Co-developed-by: Hillf Danton <[email protected]>
Signed-off-by: Hillf Danton <[email protected]>
Signed-off-by: Tetsuo Handa <[email protected]>
Fixes: 4342306 ("fs/ntfs3: Add file operations and implementation")
Signed-off-by: Linus Torvalds <[email protected]>

Author: Tetsuo Handa

fs/ntfs3/file.c

@@ -390,10 +390,10 @@ static int ntfs_truncate(struct inode *inode, loff_t new_size)
 
 	new_valid = ntfs_up_block(sb, min_t(u64, ni->i_valid, new_size));
 
-	ni_lock(ni);
-
 	truncate_setsize(inode, new_size);
 
+	ni_lock(ni);
+
 	down_write(&ni->file.run_lock);
 	err = attr_set_size(ni, ATTR_DATA, NULL, 0, &ni->file.run, new_size,
 			    &new_valid, ni->mi.sbi->options->prealloc, NULL);