Re: resctrl mount fail on v6.13-rc1

[Ming Lei <ming.lei@redhat.com>]

On Mon, Dec 02, 2024 at 06:47:38PM -0800, 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

[linux]# make -C tools/testing/selftests TARGETS=resctrl run_tests
make: Entering directory '/root/git/linux/tools/testing/selftests'
make[1]: Nothing to be done for 'all'.
TAP version 13
1..1
# timeout set to 120
# selftests: resctrl: resctrl_tests
# TAP version 13
# # Fail: Check kernel supports resctrl filesystem
# 1..0 # SKIP resctrl FS does not exist. Enable X86_CPU_RESCTRL config option.
ok 1 selftests: resctrl: resctrl_tests # SKIP
make: Leaving directory '/root/git/linux/tools/testing/selftests'

[linux]# grep X86_CPU_RESCTRL .config
CONFIG_X86_CPU_RESCTRL=y

Can you share how to make /sys/fs/resctrl so that I can check if the
recent changes in block tree can avoid this warning? 

> > > 
> > > 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 am also not running with any btrfs filesystems. 
> > 
> > Is this your usual setup in which you are seeing this the first time? Is it
> > perhaps possible for you to bisect?
> 
> Bisection says:
> 
> $ git bisect bad
> f1be1788a32e8fa63416ad4518bbd1a85a825c9d is the first bad commit
> commit f1be1788a32e8fa63416ad4518bbd1a85a825c9d
> Author: Ming Lei <ming.lei@redhat.com>
> Date:   Fri Oct 25 08:37:20 2024 +0800
> 
>     block: model freeze & enter queue as lock for supporting lockdep
> 
> > 
> > The subject states "resctrl mount fail" - could you please confirm if
> > resctrl cannot be mounted in addition to the lockdep warning?

It seems one lockdep false positive, but it shouldn't cause 'resctrl
mount fail', I will take a look at the lock chains and see if some of
them can be cut.


Thanks,
Ming