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Feedback-ID: iad51458e:Fastmail
Date: Sun, 25 Feb 2024 20:23:56 -0800
From: Boqun Feng <boqun.feng@gmail.com>
To: Hillf Danton <hdanton@sina.com>
Cc: syzbot <syzbot+c2ada45c23d98d646118@syzkaller.appspotmail.com>,
	almaz.alexandrovich@paragon-software.com,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	ntfs3@lists.linux.dev,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [ntfs3?] possible deadlock in ntfs_set_state (2)
Message-ID: <ZdwSXCaTrzq7mm7Z@boqun-archlinux>
References: <000000000000998cff06113e1d91@google.com>
 <20240213114151.982-1-hdanton@sina.com>
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In-Reply-To: <20240213114151.982-1-hdanton@sina.com>

On Tue, Feb 13, 2024 at 07:41:50PM +0800, Hillf Danton wrote:
> On Mon, 12 Feb 2024 23:12:22 -0800
> > HEAD commit:    716f4aaa7b48 Merge tag 'vfs-6.8-rc5.fixes' of git://git.ke..
> > git tree:       upstream
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=100fd062180000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=1d7c92dd8d5c7a1e
> > dashboard link: https://syzkaller.appspot.com/bug?extid=c2ada45c23d98d646118
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11fcbd48180000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17f6e642180000
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/ca4bf59e5a18/disk-716f4aaa.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/3d7ade517e63/vmlinux-716f4aaa.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/e13f7054c0c1/bzImage-716f4aaa.xz
> > mounted in repro: https://storage.googleapis.com/syzbot-assets/00ba9c2f3dd0/mount_0.gz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+c2ada45c23d98d646118@syzkaller.appspotmail.com
> > 
> > loop0: detected capacity change from 0 to 4096
> > ntfs3: loop0: Different NTFS sector size (4096) and media sector size (512).
> > ntfs3: loop0: ino=5, "/" ntfs_iget5
> > ============================================
> > WARNING: possible recursive locking detected
> > 6.8.0-rc4-syzkaller-00003-g716f4aaa7b48 #0 Not tainted
> > --------------------------------------------
> > syz-executor354/5071 is trying to acquire lock:
> > ffff888070ee0100 (&ni->ni_lock#3){+.+.}-{3:3}, at: ntfs_set_state+0x1ff/0x6c0 fs/ntfs3/fsntfs.c:947

this is a mutex_lock_nested() with a subkey 0.

> > 
> > but task is already holding lock:
> > ffff888070de3c00 (&ni->ni_lock#3){+.+.}-{3:3}, at: ni_trylock fs/ntfs3/ntfs_fs.h:1141 [inline]
> > ffff888070de3c00 (&ni->ni_lock#3){+.+.}-{3:3}, at: ni_write_inode+0x1bc/0x1010 fs/ntfs3/frecord.c:3265

These two are try locks.

> > 
> This report looks false positive but raises the question -- what made lockedp

This is not a false positive by lockdep locking rules, basically it
reported deadlock cases as the follow:

	mutex_trylock(A1);
	mutex_trylock(A2);
	mutex_lock(A1 /* or A2 */);

Two things to notice here: 1) these two trylock()s not resulting in
real deadlock cases must be because they are on different lock
instances, 2) deadlock detectors work on lock classes, so although the
mutex_lock() above may be on a different instance (say A3), currently
there is no way for lockdep to tell that. In this case, users need to
use subkeys to tell lockdep mutex_lock() and mutex_trylock() are on
different sets of instannces (i.e. sub classes). Note that subkey == 0
means the main class.

Regards,
Boqun

> pull the wrong trigger? Because of the correct lock_class_key in mutex_init()
> instead of &ni->ni_lock?
> 
> > other info that might help us debug this:
> >  Possible unsafe locking scenario:
> > 
> >        CPU0
> >        ----
> >   lock(&ni->ni_lock#3);
> >   lock(&ni->ni_lock#3);
> > 
> >  *** DEADLOCK ***
> > 
> >  May be due to missing lock nesting notation
> > 
> > 3 locks held by syz-executor354/5071:
> >  #0: ffff88802223a420 (sb_writers#9){.+.+}-{0:0}, at: do_sys_ftruncate+0x25c/0x390 fs/open.c:191
> >  #1: ffff888070de3ea0 (&sb->s_type->i_mutex_key#15){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:802 [inline]
> >  #1: ffff888070de3ea0 (&sb->s_type->i_mutex_key#15){+.+.}-{3:3}, at: do_truncate+0x20c/0x310 fs/open.c:64
> >  #2: ffff888070de3c00 (&ni->ni_lock#3){+.+.}-{3:3}, at: ni_trylock fs/ntfs3/ntfs_fs.h:1141 [inline]
> >  #2: ffff888070de3c00 (&ni->ni_lock#3){+.+.}-{3:3}, at: ni_write_inode+0x1bc/0x1010 fs/ntfs3/frecord.c:3265
> > 
> > stack backtrace:
> > CPU: 0 PID: 5071 Comm: syz-executor354 Not tainted 6.8.0-rc4-syzkaller-00003-g716f4aaa7b48 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
> >  check_deadlock kernel/locking/lockdep.c:3062 [inline]
> >  validate_chain+0x15c0/0x58e0 kernel/locking/lockdep.c:3856
> >  __lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137
> >  lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
> >  __mutex_lock_common kernel/locking/mutex.c:608 [inline]
> >  __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
> >  ntfs_set_state+0x1ff/0x6c0 fs/ntfs3/fsntfs.c:947
> >  ntfs_iget5+0x3f0/0x3b70 fs/ntfs3/inode.c:535
> >  ni_update_parent+0x943/0xdd0 fs/ntfs3/frecord.c:3218
> >  ni_write_inode+0xde9/0x1010 fs/ntfs3/frecord.c:3324
> >  ntfs_truncate fs/ntfs3/file.c:410 [inline]
> >  ntfs3_setattr+0x950/0xb40 fs/ntfs3/file.c:703
> >  notify_change+0xb9f/0xe70 fs/attr.c:499
> >  do_truncate+0x220/0x310 fs/open.c:66
> >  do_sys_ftruncate+0x2f7/0x390 fs/open.c:194
> >  do_syscall_64+0xfb/0x240
> >  entry_SYSCALL_64_after_hwframe+0x6f/0x77
> > RIP: 0033:0x7fd0ca446639
> > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007fff0baab678 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
> > RAX: ffffffffffffffda RBX: 00007fff0baab848 RCX: 00007fd0ca446639
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
> > RBP: 00007fd0ca4d8610 R08: 0000000000000000 R09: 00007fff0baab848
> > R10: 000000000001f20a R11: 0000000000000246 R12: 0000000000000001
> > R13: 00007fff0baab838 R14: 0000000000000001 R15: 0000000000000001
> >  </TASK>
> > 
> > 
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@googlegroups.com.
> > 
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > 
> > If the report is already addressed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> > 
> > If you want syzbot to run the reproducer, reply with:
> > #syz test: git://repo/address.git branch-or-commit-hash
> > If you attach or paste a git patch, syzbot will apply it before testing.
> > 
> > If you want to overwrite report's subsystems, reply with:
> > #syz set subsystems: new-subsystem
> > (See the list of subsystem names on the web dashboard)
> > 
> > If the report is a duplicate of another one, reply with:
> > #syz dup: exact-subject-of-another-report
> > 
> > If you want to undo deduplication, reply with:
> > #syz undup
> >