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Date: Sun, 9 Sep 2018 12:11:04 -0700
From: Matthew Wilcox <willy@infradead.org>
To: syzbot <syzbot+d86c4426a01f60feddc7@syzkaller.appspotmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>, bcrl@kvack.org,
        linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        viro@zeniv.linux.org.uk
Subject: Re: possible deadlock in free_ioctx_users
Message-ID: <20180909191104.GB20237@bombadil.infradead.org>
References: <00000000000024df4605757495a8@google.com>
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I would be inclined to blame FUSE for this problem.

On Sun, Sep 09, 2018 at 11:41:02AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    f8f65382c98a Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=113260ae400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8f59875069d721b6
> dashboard link: https://syzkaller.appspot.com/bug?extid=d86c4426a01f60feddc7
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120baa9e400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13979cbe400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+d86c4426a01f60feddc7@syzkaller.appspotmail.com
> 
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> 
> ========================================================
> WARNING: possible irq lock inversion dependency detected
> 4.19.0-rc2+ #229 Not tainted
> --------------------------------------------------------
> swapper/0/0 just changed the state of lock:
> 00000000c02bddef (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq
> include/linux/spinlock.h:354 [inline]
> 00000000c02bddef (&(&ctx->ctx_lock)->rlock){..-.}, at:
> free_ioctx_users+0xbc/0x710 fs/aio.c:603
> but this lock took another, SOFTIRQ-unsafe lock in the past:
>  (&fiq->waitq){+.+.}
> 
> 
> and interrupts could create inverse lock ordering between them.
> 
> 
> other info that might help us debug this:
>  Possible interrupt unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(&fiq->waitq);
>                                local_irq_disable();
>                                lock(&(&ctx->ctx_lock)->rlock);
>                                lock(&fiq->waitq);
>   <Interrupt>
>     lock(&(&ctx->ctx_lock)->rlock);
> 
>  *** DEADLOCK ***
> 
> 2 locks held by swapper/0/0:
>  #0: 0000000077c9a56b (rcu_callback){....}, at: __rcu_reclaim
> kernel/rcu/rcu.h:226 [inline]
>  #0: 0000000077c9a56b (rcu_callback){....}, at: rcu_do_batch
> kernel/rcu/tree.c:2576 [inline]
>  #0: 0000000077c9a56b (rcu_callback){....}, at: invoke_rcu_callbacks
> kernel/rcu/tree.c:2880 [inline]
>  #0: 0000000077c9a56b (rcu_callback){....}, at: __rcu_process_callbacks
> kernel/rcu/tree.c:2847 [inline]
>  #0: 0000000077c9a56b (rcu_callback){....}, at:
> rcu_process_callbacks+0x1012/0x2670 kernel/rcu/tree.c:2864
>  #1: 0000000031dcf310 (rcu_read_lock_sched){....}, at:
> percpu_ref_call_confirm_rcu lib/percpu-refcount.c:119 [inline]
>  #1: 0000000031dcf310 (rcu_read_lock_sched){....}, at:
> percpu_ref_switch_to_atomic_rcu+0x2b7/0x820 lib/percpu-refcount.c:158
> 
> the shortest dependencies between 2nd lock and 1st lock:
>  -> (&fiq->waitq){+.+.} ops: 4 {
>     HARDIRQ-ON-W at:
>                       lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3901
>                       __raw_spin_lock include/linux/spinlock_api_smp.h:142
> [inline]
>                       _raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:144
>                       spin_lock include/linux/spinlock.h:329 [inline]
>                       flush_bg_queue+0x389/0x650 fs/fuse/dev.c:364
>                       fuse_request_send_background_locked+0x2f5/0x5a0
> fs/fuse/dev.c:598
>                       fuse_request_send_background+0x135/0x180
> fs/fuse/dev.c:606
>                       cuse_send_init fs/fuse/cuse.c:458 [inline]
>                       cuse_channel_open+0x6b0/0x963 fs/fuse/cuse.c:518
>                       misc_open+0x3ca/0x560 drivers/char/misc.c:141
>                       chrdev_open+0x25a/0x710 fs/char_dev.c:417
>                       do_dentry_open+0x499/0x1250 fs/open.c:771
>                       vfs_open+0xa0/0xd0 fs/open.c:880
>                       do_last fs/namei.c:3418 [inline]
>                       path_openat+0x12bf/0x5160 fs/namei.c:3534
>                       do_filp_open+0x255/0x380 fs/namei.c:3564
>                       do_sys_open+0x568/0x700 fs/open.c:1063
>                       __do_sys_openat fs/open.c:1090 [inline]
>                       __se_sys_openat fs/open.c:1084 [inline]
>                       __x64_sys_openat+0x9d/0x100 fs/open.c:1084
>                       do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>                       entry_SYSCALL_64_after_hwframe+0x49/0xbe
>     SOFTIRQ-ON-W at:
>                       lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3901
>                       __raw_spin_lock include/linux/spinlock_api_smp.h:142
> [inline]
>                       _raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:144
>                       spin_lock include/linux/spinlock.h:329 [inline]
>                       flush_bg_queue+0x389/0x650 fs/fuse/dev.c:364
>                       fuse_request_send_background_locked+0x2f5/0x5a0
> fs/fuse/dev.c:598
>                       fuse_request_send_background+0x135/0x180
> fs/fuse/dev.c:606
>                       cuse_send_init fs/fuse/cuse.c:458 [inline]
>                       cuse_channel_open+0x6b0/0x963 fs/fuse/cuse.c:518
>                       misc_open+0x3ca/0x560 drivers/char/misc.c:141
>                       chrdev_open+0x25a/0x710 fs/char_dev.c:417
>                       do_dentry_open+0x499/0x1250 fs/open.c:771
>                       vfs_open+0xa0/0xd0 fs/open.c:880
>                       do_last fs/namei.c:3418 [inline]
>                       path_openat+0x12bf/0x5160 fs/namei.c:3534
>                       do_filp_open+0x255/0x380 fs/namei.c:3564
>                       do_sys_open+0x568/0x700 fs/open.c:1063
>                       __do_sys_openat fs/open.c:1090 [inline]
>                       __se_sys_openat fs/open.c:1084 [inline]
>                       __x64_sys_openat+0x9d/0x100 fs/open.c:1084
>                       do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>                       entry_SYSCALL_64_after_hwframe+0x49/0xbe
>     INITIAL USE at:
>                      lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3901
>                      __raw_spin_lock include/linux/spinlock_api_smp.h:142
> [inline]
>                      _raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:144
>                      spin_lock include/linux/spinlock.h:329 [inline]
>                      flush_bg_queue+0x389/0x650 fs/fuse/dev.c:364
>                      fuse_request_send_background_locked+0x2f5/0x5a0
> fs/fuse/dev.c:598
>                      fuse_request_send_background+0x135/0x180
> fs/fuse/dev.c:606
>                      cuse_send_init fs/fuse/cuse.c:458 [inline]
>                      cuse_channel_open+0x6b0/0x963 fs/fuse/cuse.c:518
>                      misc_open+0x3ca/0x560 drivers/char/misc.c:141
>                      chrdev_open+0x25a/0x710 fs/char_dev.c:417
>                      do_dentry_open+0x499/0x1250 fs/open.c:771
>                      vfs_open+0xa0/0xd0 fs/open.c:880
>                      do_last fs/namei.c:3418 [inline]
>                      path_openat+0x12bf/0x5160 fs/namei.c:3534
>                      do_filp_open+0x255/0x380 fs/namei.c:3564
>                      do_sys_open+0x568/0x700 fs/open.c:1063
>                      __do_sys_openat fs/open.c:1090 [inline]
>                      __se_sys_openat fs/open.c:1084 [inline]
>                      __x64_sys_openat+0x9d/0x100 fs/open.c:1084
>                      do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>                      entry_SYSCALL_64_after_hwframe+0x49/0xbe
>   }
>   ... key      at: [<ffffffff8b4763c0>] __key.42168+0x0/0x40
>   ... acquired at:
>    __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
>    _raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:144
>    spin_lock include/linux/spinlock.h:329 [inline]
>    aio_poll+0x760/0x1420 fs/aio.c:1747
>    io_submit_one+0xab8/0x1090 fs/aio.c:1850
>    __do_sys_io_submit fs/aio.c:1916 [inline]
>    __se_sys_io_submit fs/aio.c:1887 [inline]
>    __x64_sys_io_submit+0x1b9/0x5d0 fs/aio.c:1887
>    do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> -> (&(&ctx->ctx_lock)->rlock){..-.} ops: 2 {
>    IN-SOFTIRQ-W at:
>                     lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3901
>                     __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128
> [inline]
>                     _raw_spin_lock_irq+0x61/0x80
> kernel/locking/spinlock.c:160
>                     spin_lock_irq include/linux/spinlock.h:354 [inline]
>                     free_ioctx_users+0xbc/0x710 fs/aio.c:603
>                     percpu_ref_put_many include/linux/percpu-refcount.h:284
> [inline]
>                     percpu_ref_put include/linux/percpu-refcount.h:300
> [inline]
>                     percpu_ref_call_confirm_rcu lib/percpu-refcount.c:123
> [inline]
>                     percpu_ref_switch_to_atomic_rcu+0x62c/0x820
> lib/percpu-refcount.c:158
>                     __rcu_reclaim kernel/rcu/rcu.h:236 [inline]
>                     rcu_do_batch kernel/rcu/tree.c:2576 [inline]
>                     invoke_rcu_callbacks kernel/rcu/tree.c:2880 [inline]
>                     __rcu_process_callbacks kernel/rcu/tree.c:2847 [inline]
>                     rcu_process_callbacks+0xf23/0x2670
> kernel/rcu/tree.c:2864
>                     __do_softirq+0x30b/0xad8 kernel/softirq.c:292
>                     invoke_softirq kernel/softirq.c:372 [inline]
>                     irq_exit+0x17f/0x1c0 kernel/softirq.c:412
>                     exiting_irq arch/x86/include/asm/apic.h:536 [inline]
>                     smp_apic_timer_interrupt+0x1cb/0x760
> arch/x86/kernel/apic/apic.c:1056
>                     apic_timer_interrupt+0xf/0x20
> arch/x86/entry/entry_64.S:864
>                     native_safe_halt+0x6/0x10
> arch/x86/include/asm/irqflags.h:57
>                     arch_safe_halt arch/x86/include/asm/paravirt.h:94
> [inline]
>                     default_idle+0xbf/0x490 arch/x86/kernel/process.c:498
>                     arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:489
>                     default_idle_call+0x6d/0x90 kernel/sched/idle.c:93
>                     cpuidle_idle_call kernel/sched/idle.c:153 [inline]
>                     do_idle+0x3db/0x5b0 kernel/sched/idle.c:262
>                     cpu_startup_entry+0x10c/0x120 kernel/sched/idle.c:368
>                     rest_init+0xe2/0xe5 init/main.c:442
>                     start_kernel+0x8f4/0x92f init/main.c:739
>                     x86_64_start_reservations+0x29/0x2b
> arch/x86/kernel/head64.c:452
>                     x86_64_start_kernel+0x76/0x79
> arch/x86/kernel/head64.c:433
>                     secondary_startup_64+0xa4/0xb0
> arch/x86/kernel/head_64.S:242
>    INITIAL USE at:
>                    lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3901
>                    __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128
> [inline]
>                    _raw_spin_lock_irq+0x61/0x80
> kernel/locking/spinlock.c:160
>                    spin_lock_irq include/linux/spinlock.h:354 [inline]
>                    aio_poll+0x738/0x1420 fs/aio.c:1746
>                    io_submit_one+0xab8/0x1090 fs/aio.c:1850
>                    __do_sys_io_submit fs/aio.c:1916 [inline]
>                    __se_sys_io_submit fs/aio.c:1887 [inline]
>                    __x64_sys_io_submit+0x1b9/0x5d0 fs/aio.c:1887
>                    do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>                    entry_SYSCALL_64_after_hwframe+0x49/0xbe
>  }
>  ... key      at: [<ffffffff8b3dc960>] __key.50120+0x0/0x40
>  ... acquired at:
>    mark_lock_irq kernel/locking/lockdep.c:2756 [inline]
>    mark_lock+0xa6b/0x1cb0 kernel/locking/lockdep.c:3128
>    mark_irqflags kernel/locking/lockdep.c:3006 [inline]
>    __lock_acquire+0x15f8/0x4ec0 kernel/locking/lockdep.c:3369
>    lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3901
>    __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
>    _raw_spin_lock_irq+0x61/0x80 kernel/locking/spinlock.c:160
>    spin_lock_irq include/linux/spinlock.h:354 [inline]
>    free_ioctx_users+0xbc/0x710 fs/aio.c:603
>    percpu_ref_put_many include/linux/percpu-refcount.h:284 [inline]
>    percpu_ref_put include/linux/percpu-refcount.h:300 [inline]
>    percpu_ref_call_confirm_rcu lib/percpu-refcount.c:123 [inline]
>    percpu_ref_switch_to_atomic_rcu+0x62c/0x820 lib/percpu-refcount.c:158
>    __rcu_reclaim kernel/rcu/rcu.h:236 [inline]
>    rcu_do_batch kernel/rcu/tree.c:2576 [inline]
>    invoke_rcu_callbacks kernel/rcu/tree.c:2880 [inline]
>    __rcu_process_callbacks kernel/rcu/tree.c:2847 [inline]
>    rcu_process_callbacks+0xf23/0x2670 kernel/rcu/tree.c:2864
>    __do_softirq+0x30b/0xad8 kernel/softirq.c:292
>    invoke_softirq kernel/softirq.c:372 [inline]
>    irq_exit+0x17f/0x1c0 kernel/softirq.c:412
>    exiting_irq arch/x86/include/asm/apic.h:536 [inline]
>    smp_apic_timer_interrupt+0x1cb/0x760 arch/x86/kernel/apic/apic.c:1056
>    apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:864
>    native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:57
>    arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
>    default_idle+0xbf/0x490 arch/x86/kernel/process.c:498
>    arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:489
>    default_idle_call+0x6d/0x90 kernel/sched/idle.c:93
>    cpuidle_idle_call kernel/sched/idle.c:153 [inline]
>    do_idle+0x3db/0x5b0 kernel/sched/idle.c:262
>    cpu_startup_entry+0x10c/0x120 kernel/sched/idle.c:368
>    rest_init+0xe2/0xe5 init/main.c:442
>    start_kernel+0x8f4/0x92f init/main.c:739
>    x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:452
>    x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:433
>    secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:242
> 
> 
> stack backtrace:
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.19.0-rc2+ #229
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
>  print_irq_inversion_bug.part.35+0x2c7/0x2d6 kernel/locking/lockdep.c:2622
>  print_irq_inversion_bug kernel/locking/lockdep.c:2625 [inline]
>  check_usage_forwards.cold.57+0x20/0x29 kernel/locking/lockdep.c:2647
>  mark_lock_irq kernel/locking/lockdep.c:2756 [inline]
>  mark_lock+0xa6b/0x1cb0 kernel/locking/lockdep.c:3128
>  mark_irqflags kernel/locking/lockdep.c:3006 [inline]
>  __lock_acquire+0x15f8/0x4ec0 kernel/locking/lockdep.c:3369
>  lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3901
>  __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
>  _raw_spin_lock_irq+0x61/0x80 kernel/locking/spinlock.c:160
>  spin_lock_irq include/linux/spinlock.h:354 [inline]
>  free_ioctx_users+0xbc/0x710 fs/aio.c:603
>  percpu_ref_put_many include/linux/percpu-refcount.h:284 [inline]
>  percpu_ref_put include/linux/percpu-refcount.h:300 [inline]
>  percpu_ref_call_confirm_rcu lib/percpu-refcount.c:123 [inline]
>  percpu_ref_switch_to_atomic_rcu+0x62c/0x820 lib/percpu-refcount.c:158
>  __rcu_reclaim kernel/rcu/rcu.h:236 [inline]
>  rcu_do_batch kernel/rcu/tree.c:2576 [inline]
>  invoke_rcu_callbacks kernel/rcu/tree.c:2880 [inline]
>  __rcu_process_callbacks kernel/rcu/tree.c:2847 [inline]
>  rcu_process_callbacks+0xf23/0x2670 kernel/rcu/tree.c:2864
>  __do_softirq+0x30b/0xad8 kernel/softirq.c:292
>  invoke_softirq kernel/softirq.c:372 [inline]
>  irq_exit+0x17f/0x1c0 kernel/softirq.c:412
>  exiting_irq arch/x86/include/asm/apic.h:536 [inline]
>  smp_apic_timer_interrupt+0x1cb/0x760 arch/x86/kernel/apic/apic.c:1056
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:864
>  </IRQ>
> RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:57
> Code: e9 2c ff ff ff 48 89 c7 48 89 45 d8 e8 43 b9 02 fa 48 8b 45 d8 e9 ca
> fe ff ff 48 89 df e8 32 b9 02 fa eb 82 55 48 89 e5 fb f4 <5d> c3 0f 1f 84 00
> 00 00 00 00 55 48 89 e5 f4 5d c3 90 90 90 90 90
> RSP: 0018:ffffffff89407bb8 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
> RAX: dffffc0000000000 RBX: 1ffffffff1280f7b RCX: 0000000000000000
> RDX: 1ffffffff12a4538 RSI: 0000000000000001 RDI: ffffffff895229c0
> RBP: ffffffff89407bb8 R08: ffffffff89475fc0 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff89407c78
> R13: ffffffff8a3149a0 R14: 0000000000000000 R15: 0000000000000000
>  arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
>  default_idle+0xbf/0x490 arch/x86/kernel/process.c:498
>  arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:489
>  default_idle_call+0x6d/0x90 kernel/sched/idle.c:93
>  cpuidle_idle_call kernel/sched/idle.c:153 [inline]
>  do_idle+0x3db/0x5b0 kernel/sched/idle.c:262
>  cpu_startup_entry+0x10c/0x120 kernel/sched/idle.c:368
>  rest_init+0xe2/0xe5 init/main.c:442
>  start_kernel+0x8f4/0x92f init/main.c:739
>  ? early_idt_handler_common+
> 
> 
> ---
> This bug 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 bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches