[syzbot] possible deadlock in snd_timer_interrupt
Desmond Cheong Zhi Xi
desmondcheongzx at gmail.com
Sun Jul 25 15:19:00 CEST 2021
On 25/7/21 8:39 pm, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: f0fddcec6b62 Merge tag 'for-5.14-rc2-tag' of git://git.ker..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13cbb70e300000
> kernel config: https://syzkaller.appspot.com/x/.config?x=5dc0e3202ae2f574
> dashboard link: https://syzkaller.appspot.com/bug?extid=17c16b868e6af41acdd4
> compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17667ecc300000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=179e0582300000
>
> The issue was bisected to:
>
> commit e918188611f073063415f40fae568fa4d86d9044
> Author: Boqun Feng <boqun.feng at gmail.com>
> Date: Fri Aug 7 07:42:20 2020 +0000
>
> locking: More accurate annotations for read_lock()
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=109610b2300000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=129610b2300000
> console output: https://syzkaller.appspot.com/x/log.txt?x=149610b2300000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+17c16b868e6af41acdd4 at syzkaller.appspotmail.com
> Fixes: e918188611f0 ("locking: More accurate annotations for read_lock()")
>
> ========================================================
> WARNING: possible irq lock inversion dependency detected
> 5.14.0-rc2-syzkaller #0 Not tainted
> --------------------------------------------------------
> syz-executor065/8431 just changed the state of lock:
> ffff888027e94148 (&timer->lock){..-.}-{2:2}, at: snd_timer_interrupt+0x210/0x1410 sound/core/timer.c:857
> but this lock took another, SOFTIRQ-READ-unsafe lock in the past:
> (&f->f_owner.lock){.+.+}-{2:2}
>
>
> and interrupts could create inverse lock ordering between them.
>
>
> other info that might help us debug this:
> Chain exists of:
> &timer->lock --> &new->fa_lock --> &f->f_owner.lock
>
> Possible interrupt unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&f->f_owner.lock);
> local_irq_disable();
> lock(&timer->lock);
> lock(&new->fa_lock);
> <Interrupt>
> lock(&timer->lock);
>
> *** DEADLOCK ***
>
> 4 locks held by syz-executor065/8431:
> #0: ffff888029390460 (sb_writers#5){.+.+}-{0:0}, at: mnt_want_write+0x3b/0x80 fs/namespace.c:375
> #1: ffff888039f60e80 (&type->i_mutex_dir_key#4/1){+.+.}-{3:3}, at: inode_lock_nested include/linux/fs.h:809 [inline]
> #1: ffff888039f60e80 (&type->i_mutex_dir_key#4/1){+.+.}-{3:3}, at: filename_create+0x19f/0x700 fs/namei.c:3602
> #2: ffffffff8c7177c0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:266
> #3: ffffc90000dc0be0 ((&priv->tlist)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
> #3: ffffc90000dc0be0 ((&priv->tlist)){+.-.}-{0:0}, at: call_timer_fn+0xbd/0x210 kernel/time/timer.c:1407
>
> the shortest dependencies between 2nd lock and 1st lock:
> -> (&f->f_owner.lock){.+.+}-{2:2} {
> HARDIRQ-ON-R at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_read_lock include/linux/rwlock_api_smp.h:149 [inline]
> _raw_read_lock+0x32/0x40 kernel/locking/spinlock.c:223
> f_getown_ex fs/fcntl.c:211 [inline]
> do_fcntl+0x150/0x1510 fs/fcntl.c:395
> __do_sys_fcntl fs/fcntl.c:471 [inline]
> __se_sys_fcntl+0xd8/0x1b0 fs/fcntl.c:456
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> SOFTIRQ-ON-R at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_read_lock include/linux/rwlock_api_smp.h:149 [inline]
> _raw_read_lock+0x32/0x40 kernel/locking/spinlock.c:223
> f_getown_ex fs/fcntl.c:211 [inline]
> do_fcntl+0x150/0x1510 fs/fcntl.c:395
> __do_sys_fcntl fs/fcntl.c:471 [inline]
> __se_sys_fcntl+0xd8/0x1b0 fs/fcntl.c:456
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> INITIAL READ USE at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_read_lock_irqsave include/linux/rwlock_api_smp.h:159 [inline]
> _raw_read_lock_irqsave+0xbb/0x100 kernel/locking/spinlock.c:231
> send_sigio+0x2f/0x300 fs/fcntl.c:795
> kill_fasync_rcu fs/fcntl.c:1019 [inline]
> kill_fasync+0x1e3/0x430 fs/fcntl.c:1033
> snd_timer_user_ccallback+0x3ee/0x710 sound/core/timer.c:1387
> snd_timer_notify1+0x19e/0x340 sound/core/timer.c:516
> snd_timer_start1+0x53d/0x640 sound/core/timer.c:578
> snd_timer_start sound/core/timer.c:697 [inline]
> snd_timer_user_start sound/core/timer.c:1985 [inline]
> __snd_timer_user_ioctl+0xe18/0x5ed0 sound/core/timer.c:2108
> snd_timer_user_ioctl+0x5d/0x80 sound/core/timer.c:2129
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:1069 [inline]
> __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> }
> ... key at: [<ffffffff907d04a0>] __alloc_file.__key+0x0/0x10
> ... acquired at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_read_lock_irqsave include/linux/rwlock_api_smp.h:159 [inline]
> _raw_read_lock_irqsave+0xbb/0x100 kernel/locking/spinlock.c:231
> send_sigio+0x2f/0x300 fs/fcntl.c:795
> kill_fasync_rcu fs/fcntl.c:1019 [inline]
> kill_fasync+0x1e3/0x430 fs/fcntl.c:1033
> snd_timer_user_ccallback+0x3ee/0x710 sound/core/timer.c:1387
> snd_timer_notify1+0x19e/0x340 sound/core/timer.c:516
> snd_timer_start1+0x53d/0x640 sound/core/timer.c:578
> snd_timer_start sound/core/timer.c:697 [inline]
> snd_timer_user_start sound/core/timer.c:1985 [inline]
> __snd_timer_user_ioctl+0xe18/0x5ed0 sound/core/timer.c:2108
> snd_timer_user_ioctl+0x5d/0x80 sound/core/timer.c:2129
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:1069 [inline]
> __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> -> (&new->fa_lock){....}-{2:2} {
> INITIAL USE at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_write_lock_irq include/linux/rwlock_api_smp.h:196 [inline]
> _raw_write_lock_irq+0xae/0xf0 kernel/locking/spinlock.c:311
> fasync_remove_entry+0xff/0x1d0 fs/fcntl.c:890
> __fput+0x65b/0x7b0 fs/file_table.c:277
> task_work_run+0x146/0x1c0 kernel/task_work.c:164
> exit_task_work include/linux/task_work.h:32 [inline]
> do_exit+0x72b/0x2510 kernel/exit.c:825
> do_group_exit+0x168/0x2d0 kernel/exit.c:922
> get_signal+0x16b0/0x2080 kernel/signal.c:2808
> arch_do_signal_or_restart+0x8e/0x6d0 arch/x86/kernel/signal.c:865
> handle_signal_work kernel/entry/common.c:148 [inline]
> exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
> exit_to_user_mode_prepare+0x191/0x220 kernel/entry/common.c:209
> __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
> syscall_exit_to_user_mode+0x26/0x60 kernel/entry/common.c:302
> do_syscall_64+0x4c/0xb0 arch/x86/entry/common.c:86
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> INITIAL READ USE at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_read_lock include/linux/rwlock_api_smp.h:149 [inline]
> _raw_read_lock+0x32/0x40 kernel/locking/spinlock.c:223
> kill_fasync_rcu fs/fcntl.c:1012 [inline]
> kill_fasync+0x13b/0x430 fs/fcntl.c:1033
> snd_timer_user_ccallback+0x3ee/0x710 sound/core/timer.c:1387
> snd_timer_notify1+0x19e/0x340 sound/core/timer.c:516
> snd_timer_start1+0x53d/0x640 sound/core/timer.c:578
> snd_timer_start sound/core/timer.c:697 [inline]
> snd_timer_user_start sound/core/timer.c:1985 [inline]
> __snd_timer_user_ioctl+0xe18/0x5ed0 sound/core/timer.c:2108
> snd_timer_user_ioctl+0x5d/0x80 sound/core/timer.c:2129
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:1069 [inline]
> __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> }
> ... key at: [<ffffffff907d1360>] fasync_insert_entry.__key+0x0/0x40
> ... acquired at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_read_lock include/linux/rwlock_api_smp.h:149 [inline]
> _raw_read_lock+0x32/0x40 kernel/locking/spinlock.c:223
> kill_fasync_rcu fs/fcntl.c:1012 [inline]
> kill_fasync+0x13b/0x430 fs/fcntl.c:1033
> snd_timer_user_ccallback+0x3ee/0x710 sound/core/timer.c:1387
> snd_timer_notify1+0x19e/0x340 sound/core/timer.c:516
> snd_timer_start1+0x53d/0x640 sound/core/timer.c:578
> snd_timer_start sound/core/timer.c:697 [inline]
> snd_timer_user_start sound/core/timer.c:1985 [inline]
> __snd_timer_user_ioctl+0xe18/0x5ed0 sound/core/timer.c:2108
> snd_timer_user_ioctl+0x5d/0x80 sound/core/timer.c:2129
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:1069 [inline]
> __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> -> (&timer->lock){..-.}-{2:2} {
> IN-SOFTIRQ-W at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0xb3/0x100 kernel/locking/spinlock.c:159
> snd_timer_interrupt+0x210/0x1410 sound/core/timer.c:857
> call_timer_fn+0xf6/0x210 kernel/time/timer.c:1417
> expire_timers kernel/time/timer.c:1462 [inline]
> __run_timers+0x6ff/0x910 kernel/time/timer.c:1731
> run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1744
> __do_softirq+0x372/0x783 kernel/softirq.c:558
> invoke_softirq kernel/softirq.c:432 [inline]
> __irq_exit_rcu+0x21b/0x260 kernel/softirq.c:636
> irq_exit_rcu+0x5/0x20 kernel/softirq.c:648
> sysvec_apic_timer_interrupt+0x91/0xb0 arch/x86/kernel/apic/apic.c:1100
> asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
> __preempt_count_add arch/x86/include/asm/preempt.h:80 [inline]
> rcu_is_watching+0xd/0xb0 kernel/rcu/tree.c:1159
> rcu_read_lock include/linux/rcupdate.h:688 [inline]
> get_cached_acl+0x103/0x540 fs/posix_acl.c:44
> get_acl+0x20/0x2e0 fs/posix_acl.c:108
> posix_acl_create+0x119/0x560 fs/posix_acl.c:616
> ext4_init_acl+0xa6/0x3d0 fs/ext4/acl.c:282
> __ext4_new_inode+0x44e7/0x5810 fs/ext4/ialloc.c:1316
> ext4_mkdir+0x3fa/0xc10 fs/ext4/namei.c:2921
> vfs_mkdir+0x451/0x630 fs/namei.c:3823
> do_mkdirat+0x267/0x3e0 fs/namei.c:3848
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> INITIAL USE at:
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0xb3/0x100 kernel/locking/spinlock.c:159
> snd_timer_resolution sound/core/timer.c:489 [inline]
> snd_timer_user_params sound/core/timer.c:1852 [inline]
> __snd_timer_user_ioctl+0x1df7/0x5ed0 sound/core/timer.c:2101
> snd_timer_user_ioctl+0x5d/0x80 sound/core/timer.c:2129
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:1069 [inline]
> __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> }
> ... key at: [<ffffffff90b60220>] snd_timer_new.__key+0x0/0x40
> ... acquired at:
> mark_usage kernel/locking/lockdep.c:4488 [inline]
> __lock_acquire+0xca1/0x6100 kernel/locking/lockdep.c:4969
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0xb3/0x100 kernel/locking/spinlock.c:159
> snd_timer_interrupt+0x210/0x1410 sound/core/timer.c:857
> call_timer_fn+0xf6/0x210 kernel/time/timer.c:1417
> expire_timers kernel/time/timer.c:1462 [inline]
> __run_timers+0x6ff/0x910 kernel/time/timer.c:1731
> run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1744
> __do_softirq+0x372/0x783 kernel/softirq.c:558
> invoke_softirq kernel/softirq.c:432 [inline]
> __irq_exit_rcu+0x21b/0x260 kernel/softirq.c:636
> irq_exit_rcu+0x5/0x20 kernel/softirq.c:648
> sysvec_apic_timer_interrupt+0x91/0xb0 arch/x86/kernel/apic/apic.c:1100
> asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
> __preempt_count_add arch/x86/include/asm/preempt.h:80 [inline]
> rcu_is_watching+0xd/0xb0 kernel/rcu/tree.c:1159
> rcu_read_lock include/linux/rcupdate.h:688 [inline]
> get_cached_acl+0x103/0x540 fs/posix_acl.c:44
> get_acl+0x20/0x2e0 fs/posix_acl.c:108
> posix_acl_create+0x119/0x560 fs/posix_acl.c:616
> ext4_init_acl+0xa6/0x3d0 fs/ext4/acl.c:282
> __ext4_new_inode+0x44e7/0x5810 fs/ext4/ialloc.c:1316
> ext4_mkdir+0x3fa/0xc10 fs/ext4/namei.c:2921
> vfs_mkdir+0x451/0x630 fs/namei.c:3823
> do_mkdirat+0x267/0x3e0 fs/namei.c:3848
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
>
> stack backtrace:
> CPU: 1 PID: 8431 Comm: syz-executor065 Not tainted 5.14.0-rc2-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> <IRQ>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x1ae/0x29f lib/dump_stack.c:105
> print_irq_inversion_bug+0xa58/0xda0 kernel/locking/lockdep.c:4000
> check_usage_forwards kernel/locking/lockdep.c:2585 [inline]
> mark_lock_irq kernel/locking/lockdep.c:4163 [inline]
> mark_lock+0x1064/0x1eb0 kernel/locking/lockdep.c:4593
> mark_usage kernel/locking/lockdep.c:4488 [inline]
> __lock_acquire+0xca1/0x6100 kernel/locking/lockdep.c:4969
> lock_acquire+0x182/0x4a0 kernel/locking/lockdep.c:5625
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0xb3/0x100 kernel/locking/spinlock.c:159
> snd_timer_interrupt+0x210/0x1410 sound/core/timer.c:857
> call_timer_fn+0xf6/0x210 kernel/time/timer.c:1417
> expire_timers kernel/time/timer.c:1462 [inline]
> __run_timers+0x6ff/0x910 kernel/time/timer.c:1731
> run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1744
> __do_softirq+0x372/0x783 kernel/softirq.c:558
> invoke_softirq kernel/softirq.c:432 [inline]
> __irq_exit_rcu+0x21b/0x260 kernel/softirq.c:636
> irq_exit_rcu+0x5/0x20 kernel/softirq.c:648
> sysvec_apic_timer_interrupt+0x91/0xb0 arch/x86/kernel/apic/apic.c:1100
> </IRQ>
> asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
> RIP: 0010:rcu_dynticks_curr_cpu_in_eqs kernel/rcu/tree.c:339 [inline]
> RIP: 0010:rcu_is_watching+0xd/0xb0 kernel/rcu/tree.c:1160
> Code: 41 5e 41 5f 5d c3 e8 92 a8 6d 08 41 f7 c4 00 02 00 00 75 b6 eb b5 e8 62 a8 6d 08 66 90 41 57 41 56 53 65 83 05 4b e3 96 7e 01 <e8> 1e bb 6d 08 89 c3 83 f8 08 73 74 49 bf 00 00 00 00 00 fc ff df
> RSP: 0018:ffffc9000164f820 EFLAGS: 00000282
> RAX: 12a9aafecb760900 RBX: 1ffff920002c9f0c RCX: ffffffff816213c5
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: ffffc9000164f8e8 R08: dffffc0000000000 R09: fffffbfff1f5e1b1
> R10: fffffbfff1f5e1b1 R11: 0000000000000000 R12: 0000000000004000
> R13: dffffc0000000000 R14: 1ffff920002c9f10 R15: ffff888039f60d48
> rcu_read_lock include/linux/rcupdate.h:688 [inline]
> get_cached_acl+0x103/0x540 fs/posix_acl.c:44
> get_acl+0x20/0x2e0 fs/posix_acl.c:108
> posix_acl_create+0x119/0x560 fs/posix_acl.c:616
> ext4_init_acl+0xa6/0x3d0 fs/ext4/acl.c:282
> __ext4_new_inode+0x44e7/0x5810 fs/ext4/ialloc.c:1316
> ext4_mkdir+0x3fa/0xc10 fs/ext4/namei.c:2921
> vfs_mkdir+0x451/0x630 fs/namei.c:3823
> do_mkdirat+0x267/0x3e0 fs/namei.c:3848
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x445d87
> Code: 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 53 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffc332de6a8 EFLAGS: 00000202 ORIG_RAX: 0000000000000053
> RAX: ffffffffffffffda RBX: 000000000000e3bb RCX: 0000000000445d87
> RDX: 0000000000000000 RSI: 00000000000001ff RDI: 00007ffc332de740
> RBP: 0000000000002ebc R08: 0000000000000000 R09: 0000000000000005
> R10: 00007ffc332de445 R11: 0000000000000202 R12: 00007ffc332de6e4
> R13: 00007ffc332de740 R14: 00000000000000bd R15: 431bde82d7b634db
>
>
> ---
> 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 at googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
#syz fix: fcntl: fix potential deadlocks for &fown_struct.lock
This deadlock has the same root cause, and thus the same fix [1], as
"possible deadlock in do_fcntl" [2].
[1]:
https://lore.kernel.org/lkml/20210702091831.615042-2-desmondcheongzx@gmail.com/
[2]:
https://syzkaller.appspot.com/bug?id=923cfc6c6348963f99886a0176ef11dcc429547b
Best,
Desmond
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