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Date:   Tue, 11 Apr 2023 12:11:52 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     jack@suse.com
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com,
        syzbot <syzbot+cdcd444e4d3a256ada13@syzkaller.appspotmail.com>,
        syzbot <syzbot+aacb82fca60873422114@syzkaller.appspotmail.com>
Subject: Re: [syzbot] [fs?] possible deadlock in quotactl_fd
Message-ID: <20230411-sendung-apokalypse-05af1adb8889@brauner>
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 <000000000000ee3a3005f909f30a@google.com>
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On Mon, Apr 10, 2023 at 11:53:46PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    0d3eb744aed4 Merge tag 'urgent-rcu.2023.04.07a' of git://g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11798e4bc80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c21559e740385326
> dashboard link: https://syzkaller.appspot.com/bug?extid=cdcd444e4d3a256ada13
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/a02928003efa/disk-0d3eb744.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/7839447005a4/vmlinux-0d3eb744.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/d26ab3184148/bzImage-0d3eb744.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+cdcd444e4d3a256ada13@syzkaller.appspotmail.com
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.3.0-rc6-syzkaller-00016-g0d3eb744aed4 #0 Not tainted
> ------------------------------------------------------
> syz-executor.3/11858 is trying to acquire lock:
> ffff88802a3bc0e0 (&type->s_umount_key#31){++++}-{3:3}, at: __do_sys_quotactl_fd+0x174/0x3f0 fs/quota/quota.c:997
> 
> but task is already holding lock:
> ffff88802a3bc460 (sb_writers#4){.+.+}-{0:0}, at: __do_sys_quotactl_fd+0xd3/0x3f0 fs/quota/quota.c:990
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #1 (sb_writers#4){.+.+}-{0:0}:
>        percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
>        __sb_start_write include/linux/fs.h:1477 [inline]
>        sb_start_write include/linux/fs.h:1552 [inline]
>        write_mmp_block+0xc4/0x820 fs/ext4/mmp.c:50
>        ext4_multi_mount_protect+0x50d/0xac0 fs/ext4/mmp.c:343
>        __ext4_remount fs/ext4/super.c:6543 [inline]
>        ext4_reconfigure+0x242b/0x2b60 fs/ext4/super.c:6642
>        reconfigure_super+0x40c/0xa30 fs/super.c:956
>        vfs_fsconfig_locked fs/fsopen.c:254 [inline]
>        __do_sys_fsconfig+0xa3a/0xc20 fs/fsopen.c:439
>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>        do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> -> #0 (&type->s_umount_key#31){++++}-{3:3}:
>        check_prev_add kernel/locking/lockdep.c:3098 [inline]
>        check_prevs_add kernel/locking/lockdep.c:3217 [inline]
>        validate_chain kernel/locking/lockdep.c:3832 [inline]
>        __lock_acquire+0x2ec7/0x5d40 kernel/locking/lockdep.c:5056
>        lock_acquire kernel/locking/lockdep.c:5669 [inline]
>        lock_acquire+0x1af/0x520 kernel/locking/lockdep.c:5634
>        down_write+0x92/0x200 kernel/locking/rwsem.c:1573
>        __do_sys_quotactl_fd+0x174/0x3f0 fs/quota/quota.c:997
>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>        do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> other info that might help us debug this:
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(sb_writers#4);
>                                lock(&type->s_umount_key#31);
>                                lock(sb_writers#4);
>   lock(&type->s_umount_key#31);
> 
>  *** DEADLOCK ***

Hmkay, I understand how this happens, I think:

fsconfig(FSCONFIG_CMD_RECONFIGURE)                      quotactl_fd(Q_QUOTAON/Q_QUOTAOFF/Q_XQUOTAON/Q_XQUOTAOFF)
							-> mnt_want_write(f.file->f_path.mnt);
-> down_write(&sb->s_umount);                              -> __sb_start_write(sb, SB_FREEZE_WRITE) 
-> reconfigure_super(fc);
   -> ext4_multi_mount_protect()
      -> __sb_start_write(sb, SB_FREEZE_WRITE)         -> down_write(&sb->s_umount);
-> up_write(&sb->s_umount);

I have to step away from the computer now for a bit but naively it seem
that the locking order for quotactl_fd() should be the other way around.

But while I'm here, why does quotactl_fd() take mnt_want_write() but
quotactl() doesn't? It seems that if one needs to take it both need to
take it.

> 
> 1 lock held by syz-executor.3/11858:
>  #0: ffff88802a3bc460 (sb_writers#4){.+.+}-{0:0}, at: __do_sys_quotactl_fd+0xd3/0x3f0 fs/quota/quota.c:990
> 
> stack backtrace:
> CPU: 0 PID: 11858 Comm: syz-executor.3 Not tainted 6.3.0-rc6-syzkaller-00016-g0d3eb744aed4 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
>  check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2178
>  check_prev_add kernel/locking/lockdep.c:3098 [inline]
>  check_prevs_add kernel/locking/lockdep.c:3217 [inline]
>  validate_chain kernel/locking/lockdep.c:3832 [inline]
>  __lock_acquire+0x2ec7/0x5d40 kernel/locking/lockdep.c:5056
>  lock_acquire kernel/locking/lockdep.c:5669 [inline]
>  lock_acquire+0x1af/0x520 kernel/locking/lockdep.c:5634
>  down_write+0x92/0x200 kernel/locking/rwsem.c:1573
>  __do_sys_quotactl_fd+0x174/0x3f0 fs/quota/quota.c:997
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f81d2e8c169
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 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:00007f81d3b29168 EFLAGS: 00000246 ORIG_RAX: 00000000000001bb
> RAX: ffffffffffffffda RBX: 00007f81d2fabf80 RCX: 00007f81d2e8c169
> RDX: 0000000000000000 RSI: ffffffff80000300 RDI: 0000000000000003
> RBP: 00007f81d2ee7ca1 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fffeeb18d7f R14: 00007f81d3b29300 R15: 0000000000022000
>  </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.

On Mon, Apr 10, 2023 at 11:53:46PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    76f598ba7d8e Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13965b21c80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5666fa6aca264e42
> dashboard link: https://syzkaller.appspot.com/bug?extid=aacb82fca60873422114
> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1f01c9748997/disk-76f598ba.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b3afb4fc86b9/vmlinux-76f598ba.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/8908040d7a31/bzImage-76f598ba.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+aacb82fca60873422114@syzkaller.appspotmail.com
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.3.0-rc5-syzkaller-00022-g76f598ba7d8e #0 Not tainted
> ------------------------------------------------------
> syz-executor.0/17940 is trying to acquire lock:
> ffff88802a89e0e0 (&type->s_umount_key#31){++++}-{3:3}, at: __do_sys_quotactl_fd fs/quota/quota.c:999 [inline]
> ffff88802a89e0e0 (&type->s_umount_key#31){++++}-{3:3}, at: __se_sys_quotactl_fd+0x2fb/0x440 fs/quota/quota.c:972
> 
> but task is already holding lock:
> ffff88802a89e460 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:394
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #1 (sb_writers#4){.+.+}-{0:0}:
>        lock_acquire+0x1e1/0x520 kernel/locking/lockdep.c:5669
>        percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
>        __sb_start_write include/linux/fs.h:1477 [inline]
>        sb_start_write include/linux/fs.h:1552 [inline]
>        write_mmp_block+0xe5/0x930 fs/ext4/mmp.c:50
>        ext4_multi_mount_protect+0x364/0x990 fs/ext4/mmp.c:343
>        __ext4_remount fs/ext4/super.c:6543 [inline]
>        ext4_reconfigure+0x29a8/0x3280 fs/ext4/super.c:6642
>        reconfigure_super+0x3c9/0x7c0 fs/super.c:956
>        vfs_fsconfig_locked fs/fsopen.c:254 [inline]
>        __do_sys_fsconfig fs/fsopen.c:439 [inline]
>        __se_sys_fsconfig+0xa29/0xf70 fs/fsopen.c:314
>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>        do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> -> #0 (&type->s_umount_key#31){++++}-{3:3}:
>        check_prev_add kernel/locking/lockdep.c:3098 [inline]
>        check_prevs_add kernel/locking/lockdep.c:3217 [inline]
>        validate_chain+0x166b/0x58e0 kernel/locking/lockdep.c:3832
>        __lock_acquire+0x125b/0x1f80 kernel/locking/lockdep.c:5056
>        lock_acquire+0x1e1/0x520 kernel/locking/lockdep.c:5669
>        down_read+0x3d/0x50 kernel/locking/rwsem.c:1520
>        __do_sys_quotactl_fd fs/quota/quota.c:999 [inline]
>        __se_sys_quotactl_fd+0x2fb/0x440 fs/quota/quota.c:972
>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>        do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> other info that might help us debug this:
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(sb_writers#4);
>                                lock(&type->s_umount_key#31);
>                                lock(sb_writers#4);
>   lock(&type->s_umount_key#31);
> 
>  *** DEADLOCK ***
> 
> 1 lock held by syz-executor.0/17940:
>  #0: ffff88802a89e460 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:394
> 
> stack backtrace:
> CPU: 0 PID: 17940 Comm: syz-executor.0 Not tainted 6.3.0-rc5-syzkaller-00022-g76f598ba7d8e #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
>  check_noncircular+0x2fe/0x3b0 kernel/locking/lockdep.c:2178
>  check_prev_add kernel/locking/lockdep.c:3098 [inline]
>  check_prevs_add kernel/locking/lockdep.c:3217 [inline]
>  validate_chain+0x166b/0x58e0 kernel/locking/lockdep.c:3832
>  __lock_acquire+0x125b/0x1f80 kernel/locking/lockdep.c:5056
>  lock_acquire+0x1e1/0x520 kernel/locking/lockdep.c:5669
>  down_read+0x3d/0x50 kernel/locking/rwsem.c:1520
>  __do_sys_quotactl_fd fs/quota/quota.c:999 [inline]
>  __se_sys_quotactl_fd+0x2fb/0x440 fs/quota/quota.c:972
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f3c2aa8c169
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 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:00007f3c2b826168 EFLAGS: 00000246 ORIG_RAX: 00000000000001bb
> RAX: ffffffffffffffda RBX: 00007f3c2ababf80 RCX: 00007f3c2aa8c169
> RDX: ffffffffffffffff RSI: ffffffff80000601 RDI: 0000000000000003
> RBP: 00007f3c2aae7ca1 R08: 0000000000000000 R09: 0000000000000000
> R10: 00000000200024c0 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007ffd71f38adf R14: 00007f3c2b826300 R15: 0000000000022000
>  </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.