Re: resctrl mount fail on v6.13-rc1

[Fenghua Yu <fenghua.yu@intel.com>]

Hi, Tony and Reinette,

On 12/2/24 14:46, Luck, Tony wrote:
> On Mon, Dec 02, 2024 at 02:26:48PM -0800, Reinette Chatre wrote:
>> Hi Tony,
>>
>> On 12/2/24 1:42 PM, Luck, Tony wrote:
>>> Anyone better a decoding lockdep dumps then me make sense of this?
>>>
>>> All I did was build v6.13-rc1 with (among others)
>>>
>>> CONFIG_PROVE_LOCKING=y
>>> CONFIG_PROVE_RAW_LOCK_NESTING=y
>>> CONFIG_PROVE_RCU=y
>>>
>>> and then mount the resctrl filesystem:
>>>
>>> $ sudo mount -t resctrl resctrl /sys/fs/resctrl
>>>
>>> There are only trivial changes to the resctrl code between
>>> v6.12 (which works) and v6.13-rc1:
>>>
>>> $ git log --oneline v6.13-rc1 ^v6.12 -- arch/x86/kernel/cpu/resctrl
>>> 5a4b3fbb4849 Merge tag 'x86_cache_for_v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
>>> 9bce6e94c4b3 x86/resctrl: Support Sub-NUMA cluster mode SNC6
>>> 29eaa7958367 x86/resctrl: Slightly clean-up mbm_config_show()
>>>
>>> So something in kernfs? Or the way resctrl uses kernfs?
>>
>> I am not seeing this but that may be because I am not testing with
>> selinux enabled. My test kernel has:
>> # CONFIG_SECURITY_SELINUX is not set
> 
> I did have SELINUX configured. Disabling this CONFIG option
> makes the lockdep splat go away.
>>
>> I am also not running with any btrfs filesystems.
> 
> My root and home filesystems are btrfs, so difficult to
> check if this is also connected.
>>
>> Is this your usual setup in which you are seeing this the first time? Is it
>> perhaps possible for you to bisect?
>>
>> The subject states "resctrl mount fail" - could you please confirm if
>> resctrl cannot be mounted in addition to the lockdep warning?
> 
> The filesystem did get mounted despite all the lockdep noise.
> 
>>
>> Reinette
> 
> -Tony

I did see a similar warning on ksoftirqd before mount resctrl during 
boot time:

[   65.611812] WARNING: possible circular locking dependency detected
[   65.611813] 6.13.0-rc1-dsa+ #62 Not tainted
[   65.611814] ------------------------------------------------------
[   65.611815] ksoftirqd/4/44 is trying to acquire lock:
[   65.611817] ffffffffa787fbb8 ((console_sem).lock){....}-{2:2}, at: 
down_trylock+0x13/0x40
[   65.611829]
                but task is already holding lock:
[   65.611830] ff4ed95eefb32898 (&rq->__lock){-.-.}-{2:2}, at: 
raw_spin_rq_lock_nested+0x27/0x40
[   65.643035]
                which lock already depends on the new lock.

But I did not see the locking warning when mount resctrl. I don't use brtfs.

Thanks.

-Fenghua