Re: Converting dev->mutex into dev->spinlock ?

[Tetsuo Handa]

On 2023/02/07 0:45, Alan Stern wrote:
> On Mon, Feb 06, 2023 at 11:13:38PM +0900, Tetsuo Handa wrote:
>> On 2023/02/05 10:23, Alan Stern wrote:
>>> I suppose we could create separate lockdep classes for every bus_type 
>>> and device_type combination, as well as for the different sorts of 
>>> devices -- treat things like class devices separately from normal 
>>> devices, and so on.  But even then there would be trouble.
>>
>> Sorry, since I'm not familiar with devices, I can't interpret what you
>> are talking about in this response. But why don't you try test5() approach
>> in an example module shown below (i.e. treat all dev->mutex instances
>> independent to each other) ?
>>
>> Sharing mutex_init() (like test2() approach) causes false positives,
>> but allocating a key on each dev->mutex (like test5() approach) should
>> avoid false positives.
> 
> Interesting idea.  I'm doubtful that it will accomplish all that you 
> want.  After all, one of lockdep's biggest advantages is that it can 
> detect the potential for deadlocks without a deadlock actually 
> occurring.  By putting each mutex into its own class, you lose much of 
> this ability.
> 
> But who knows?  Maybe it will be a big help.
> 
> Anyway, below is a patch you can try, based on the code for your test5.  
> Let me know what happens.
> 

It boots, except lockdep_register_key() hit WARN_ON_ONCE() at
device_register(&platform_bus) from platform_bus_init(), for
platform_bus is a static object.

  struct device platform_bus = {
  	.init_name	= "platform",
  };

We need to skip lockdep_register_key()/lockdep_unregister_key() on
static "struct device" instances...

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[    0.550046][    T1] smpboot: Total of 12 processors activated (74513.31 BogoMIPS)
[    0.559082][    T1] devtmpfs: initialized
[    0.560054][    T1] ------------[ cut here ]------------
[    0.562046][    T1] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:1223 lockdep_register_key+0x1a2/0x230
[    0.564046][    T1] Modules linked in:
[    0.565050][    T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.2.0-rc7+ #16
[    0.567046][    T1] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020
[    0.569077][    T1] RIP: 0010:lockdep_register_key+0x1a2/0x230
[    0.571046][    T1] Code: 89 03 4a 89 1c e5 60 b1 e8 84 48 85 c0 0f 84 27 ff ff ff 8b 3d c7 68 f8 01 48 89 58 08 85 ff 0f 85 54 ff ff ff e9 1a ff ff ff <0f> 0b 5b 41 5c 41 5d 41 5e 5d c3 89 c6 48 c7 c7 70 41 05 85 e8 35
[    0.573046][    T1] RSP: 0000:ffffadbb00017e80 EFLAGS: 00010202
[    0.575046][    T1] RAX: 0000000000000001 RBX: ffffffff8443f5d0 RCX: 0000000000000000
[    0.577054][    T1] RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffffffff8443f5d0
[    0.579069][    T1] RBP: ffffadbb00017ea0 R08: 0000000000000003 R09: 0000000000000000
[    0.581069][    T1] R10: d6bf87c490213bdc R11: 0000000000000001 R12: ffffffff8443f5d0
[    0.583069][    T1] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[    0.585058][    T1] FS:  0000000000000000(0000) GS:ffff9b7ef6e00000(0000) knlGS:0000000000000000
[    0.587046][    T1] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.589046][    T1] CR2: ffff9b7df0202000 CR3: 000000012f011001 CR4: 0000000000370ef0
[    0.591046][    T1] Call Trace:
[    0.592310][    T1]  <TASK>
[    0.594046][    T1]  device_initialize+0x5f/0x170
[    0.595046][    T1]  device_register+0xd/0x20
[    0.597046][    T1]  platform_bus_init+0x16/0x4d
[    0.598061][    T1]  driver_init+0x2e/0x3a
[    0.600054][    T1]  kernel_init_freeable+0xc3/0x1d2
[    0.601051][    T1]  ? rest_init+0x190/0x190
[    0.603051][    T1]  kernel_init+0x15/0x120
[    0.604273][    T1]  ret_from_fork+0x1f/0x30
[    0.606058][    T1]  </TASK>
[    0.607069][    T1] irq event stamp: 38345
[    0.608284][    T1] hardirqs last  enabled at (38357): [<ffffffff830d9953>] __up_console_sem+0x53/0x60
[    0.610046][    T1] hardirqs last disabled at (38370): [<ffffffff830d9938>] __up_console_sem+0x38/0x60
[    0.613054][    T1] softirqs last  enabled at (38314): [<ffffffff838d54db>] __do_softirq+0x30b/0x46f
[    0.615061][    T1] softirqs last disabled at (38309): [<ffffffff8306e859>] irq_exit_rcu+0xb9/0xf0
[    0.617059][    T1] ---[ end trace 0000000000000000 ]---
[    0.622102][    T1] ACPI: PM: Registering ACPI NVS region [mem 0xbfeff000-0xbfefffff] (4096 bytes)
[    0.625130][    T1] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275000 ns
----------