Re: intel-dmar: possible circular locking dependency detected

[Jan Kiszka]

On 2017-09-27 15:21, Jan Kiszka wrote:
> On 2017-09-27 14:14, Jan Kiszka wrote:
>> Hi,
>>
>> while I'm triggering this with a still out-of-tree module from the
>> Jailhouse project, the potential deadlock appears to me being unrelated
>> to it. Please have a look:
>>
>> ======================================================
>> WARNING: possible circular locking dependency detected
>> 4.14.0-rc2-dbg+ #176 Tainted: G           O
>> ------------------------------------------------------
>> jailhouse/6105 is trying to acquire lock:
>> dmar_pci_bus_notifier+0x4f/0xcb
>>
>> but task is already holding lock:
>> __blocking_notifier_call_chain+0x31/0x65
>>
>> which lock already depends on the new lock.
>>
>>
>> the existing dependency chain (in reverse order) is:
>>
>> -> #1 (&(&priv->bus_notifier)->rwsem){++++}:
>>        __lock_acquire+0xed7/0x113b
>>        lock_acquire+0x148/0x1f6
>>        down_write+0x3b/0x6a
>>        blocking_notifier_chain_register+0x33/0x53
>>        bus_register_notifier+0x1c/0x1e
>>        dmar_dev_scope_init+0x2c6/0x2db
>>        intel_iommu_init+0xec/0x11c2
>>        pci_iommu_init+0x17/0x41
>>        do_one_initcall+0x90/0x143
>>        kernel_init_freeable+0x1cc/0x256
>>        kernel_init+0xe/0xf8
>>        ret_from_fork+0x2a/0x40
>>
>> -> #0 (dmar_global_lock){++++}:
>>        check_prev_add+0x112/0x65f
>>        __lock_acquire+0xed7/0x113b
>>        lock_acquire+0x148/0x1f6
>>        down_write+0x3b/0x6a
>>        dmar_pci_bus_notifier+0x4f/0xcb
>>        notifier_call_chain+0x3c/0x5e
>>        __blocking_notifier_call_chain+0x4c/0x65
>>        blocking_notifier_call_chain+0x14/0x16
>>        device_add+0x40c/0x522
>>        pci_device_add+0x1c0/0x1ce
>>        pci_scan_single_device+0x92/0x9d
>>        pci_scan_slot+0x59/0x10a
>>        jailhouse_pci_do_all_devices+0x74/0x263 [jailhouse]
>>        jailhouse_pci_virtual_root_devices_add+0x40/0x42 [jailhouse]
>>        jailhouse_cmd_enable+0x4fd/0x5e8 [jailhouse]
>>        jailhouse_ioctl+0x28/0x70 [jailhouse]
>>        vfs_ioctl+0x18/0x34
>>        do_vfs_ioctl+0x51b/0x5e3
>>        SyS_ioctl+0x50/0x7b
>>        entry_SYSCALL_64_fastpath+0x1f/0xbe
>>
>> other info that might help us debug this:
>>
>>  Possible unsafe locking scenario:
>>
>>        CPU0                    CPU1
>>        ----                    ----
>>   lock(&(&priv->bus_notifier)->rwsem);
>>                                lock(dmar_global_lock);
>>                                lock(&(&priv->bus_notifier)->rwsem);
>>   lock(dmar_global_lock);
>>
>>  *** DEADLOCK ***
>>
>> 2 locks held by jailhouse/6105:
>> jailhouse_cmd_enable+0x130/0x5e8 [jailhouse]
>> __blocking_notifier_call_chain+0x31/0x65
>>
>> stack backtrace:
>> CPU: 1 PID: 6105 Comm: jailhouse Tainted: G           O
>> 4.14.0-rc2-dbg+ #176
>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
>> rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
>> Call Trace:
>>  dump_stack+0x85/0xbe
>>  print_circular_bug+0x389/0x398
>>  ? add_lock_to_list.isra.23+0x96/0x96
>>  check_prev_add+0x112/0x65f
>>  ? kernel_text_address+0x1c/0x6a
>>  ? add_lock_to_list.isra.23+0x96/0x96
>>  __lock_acquire+0xed7/0x113b
>>  ? __lock_acquire+0xed7/0x113b
>>  lock_acquire+0x148/0x1f6
>>  ? dmar_pci_bus_notifier+0x4f/0xcb
>>  down_write+0x3b/0x6a
>>  ? dmar_pci_bus_notifier+0x4f/0xcb
>>  dmar_pci_bus_notifier+0x4f/0xcb
>>  notifier_call_chain+0x3c/0x5e
>>  __blocking_notifier_call_chain+0x4c/0x65
>>  blocking_notifier_call_chain+0x14/0x16
>>  device_add+0x40c/0x522
>>  pci_device_add+0x1c0/0x1ce
>>  pci_scan_single_device+0x92/0x9d
>>  pci_scan_slot+0x59/0x10a
>>  jailhouse_pci_do_all_devices+0x74/0x263 [jailhouse]
>>  jailhouse_pci_virtual_root_devices_add+0x40/0x42 [jailhouse]
>>  jailhouse_cmd_enable+0x4fd/0x5e8 [jailhouse]
>>  jailhouse_ioctl+0x28/0x70 [jailhouse]
>>  vfs_ioctl+0x18/0x34
>>  do_vfs_ioctl+0x51b/0x5e3
>>  ? kmem_cache_free+0x15b/0x1fa
>>  ? entry_SYSCALL_64_fastpath+0x5/0xbe
>>  ? trace_hardirqs_on_caller+0x180/0x19c
>>  SyS_ioctl+0x50/0x7b
>>  entry_SYSCALL_64_fastpath+0x1f/0xbe
>> RIP: 0033:0x7f8b3b110d87
>> RSP: 002b:00007ffc44b70088 EFLAGS: 00000206 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 0000000000000046 RCX: 00007f8b3b110d87
>> RDX: 0000000000604010 RSI: 0000000040080000 RDI: 0000000000000003
>> RBP: 0000000000604010 R08: 00007f8b3b3ade80 R09: 00000000000885d0
>> R10: 00007ffc44b6fe40 R11: 0000000000000206 R12: 00000000000025d4
>> R13: 0000000000000000 R14: 00007ffc44b714a4 R15: 0000000000000000
>>
>> Thanks,
>> Jan
>>
> 
> Oh, just realized that I already sent this report earlier this year [1]
> but didn't receive any feedback so far.
> 

Looking closer at the locking dmar does, specifically around
dmar_global_lock, it is either unneeded during the initialization path
or even more seriously broken. One example: dmar_table_init is not
consistently protected by dmar_global_lock.

Could someone elaborate on why we need that global lock for during init?

If we could drop the dmar_global_lock around bus_register_notifier in
dmar_dev_scope_init, the issue above would likely be resolved.

Jan
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