On 2 Jan 2023 17:24:24 +0900 Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> On 2023/01/02 10:40, Linus Torvalds wrote:
> > So I think that we have:
> >
> > - ntfs_truncate() gets the ni_lock (fs/ntfs3/file.c:393)
> >
> > - it then - while holding that lock - calls (on line 395):
> >
> > truncate_setsize ->
> > truncate_pagecache ->
> > truncate_inode_pages ->
> > truncate_inode_pages_range ->
> > folio_lock
> >
> > but that deadlocks on another process that wants to read that page,
> > and that needs ni_lock to do so.
> >
> > So yes, it does look like a ntfs3 deadlock involving ni_lock.
>
> Yes, I think you are right. My patch confirmed that other threads are not
> holding ni_lock lock, which means that this is a deadlock between
> PG_locked bit and ni_lock lock.
>
> filemap_update_page() calls filemap_read_folio() after calling
> folio_trylock(). Since folio_trylock() sets PG_locked bit,
>
> mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:799
> ni_lock fs/ntfs3/ntfs_fs.h:1122 [inline]
> attr_data_get_block+0x4a6/0x2e40 fs/ntfs3/attrib.c:919
> ntfs_get_block_vbo+0x374/0xd20 fs/ntfs3/inode.c:573
> do_mpage_readpage+0x98b/0x1bb0 fs/mpage.c:208
> mpage_read_folio+0x103/0x1d0 fs/mpage.c:379
> filemap_read_folio+0x1ba/0x7f0 mm/filemap.c:2426
> filemap_update_page+0x3ca/0x550 mm/filemap.c:2511
> filemap_get_pages+0x8d8/0x1110 mm/filemap.c:2624
> filemap_read+0x3e7/0xee0 mm/filemap.c:2694
>
> is trying to take ni_lock after setting PG_locked bit.
>
> On the other hand, folio_lock() waits until PG_locked bit is cleared,
> but unfortunately ntfs3_setattr() already took ni_lock before calling
> folio_lock().
>
> io_schedule+0x83/0x100 kernel/sched/core.c:8811
> folio_wait_bit_common+0x8ca/0x1390 mm/filemap.c:1297
> folio_lock include/linux/pagemap.h:938 [inline]
> truncate_inode_pages_range+0xc8d/0x1650 mm/truncate.c:421
> truncate_inode_pages mm/truncate.c:448 [inline]
> truncate_pagecache mm/truncate.c:743 [inline]
> truncate_setsize+0xcb/0xf0 mm/truncate.c:768
> ntfs_truncate fs/ntfs3/file.c:395 [inline]
> ntfs3_setattr+0x5a5/0xca0 fs/ntfs3/file.c:696
>
> Since no lockdep annotation is used for e.g. PG_locked bit, this deadlock
> cannot be detected by lockdep...
Good work, Tetsuo, thanks.
Given inode_lock before ni_lock in the reported lock chain,
> > 3 locks held by syz-executor394/5222:
> > #0: ffff88801ee04460 (sb_writers#9){.+.+}-{0:0}, at: mnt_want_write+0x3b/0x80 fs/namespace.c:508
> > #1: ffff888073930b00 (&sb->s_type->i_mutex_key#14){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:756 [inline]
> > #1: ffff888073930b00 (&sb->s_type->i_mutex_key#14){+.+.}-{3:3}, at: do_truncate+0x205/0x300 fs/open.c:63
> > #2: ffff888073930860 (&ni->ni_lock/4){+.+.}-{3:3}, at: ni_lock fs/ntfs3/ntfs_fs.h:1122 [inline]
> > #2: ffff888073930860 (&ni->ni_lock/4){+.+.}-{3:3}, at: ntfs_truncate fs/ntfs3/file.c:393 [inline]
> > #2: ffff888073930860 (&ni->ni_lock/4){+.+.}-{3:3}, at: ntfs3_setattr+0x596/0xca0 fs/ntfs3/file.c:696
a workaround is take ni_lock after truncate_setsize(). Lets see the echo
from syzbot.
#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
--- x/fs/ntfs3/file.c
+++ y/fs/ntfs3/file.c
@@ -390,10 +390,10 @@ static int ntfs_truncate(struct inode *i
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);
--
