Re: [PATCH v9 15/17] x86/split_lock: Add documentation for split lock detection interface

Thomas Gleixner
2019-06-26T21:52:19Z

On Tue, 18 Jun 2019, Fenghua Yu wrote:

> It is useful for development and debugging to document the new debugfs
> interface /sys/kernel/debug/x86/split_lock_detect.
>
> A new debugfs documentation is created to describe the split lock detection
> interface. In the future, more entries may be added in the documentation to
> describe other interfaces under /sys/kernel/debug/x86 directory.
>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> ---
> Documentation/ABI/testing/debugfs-x86 | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
> create mode 100644 Documentation/ABI/testing/debugfs-x86
>
> diff --git a/Documentation/ABI/testing/debugfs-x86 b/Documentation/ABI/testing/debugfs-x86
> new file mode 100644
> index 000000000000..17a1e9ed6712
> --- /dev/null
> +++ b/Documentation/ABI/testing/debugfs-x86
> @@ -0,0 +1,21 @@
> +What: /sys/kernel/debugfs/x86/split_lock_detect
> +Date: May 2019
> +Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
> +Description: (RW) Control split lock detection on Intel Tremont and
> + future CPUs
> +
> + Reads return split lock detection status:
> + 0: disabled
> + 1: enabled
> +
> + Writes enable or disable split lock detection:
> + The first character is one of 'Nn0' or [oO][fF] for off
> + disables the feature.
> + The first character is one of 'Yy1' or [oO][nN] for on
> + enables the feature.
> +
> + Please note the interface only shows or controls global setting.
> + During run time, split lock detection on one CPU may be
> + disabled if split lock operation in kernel code happens on
> + the CPU. The interface doesn't show or control split lock
> + detection on individual CPU.

But it should show that the debug output for the kernel has been globally
disabled instead of merily stating 'enabled' while it's already disabled on
a bunch on CPUs. I fundamentally despise inconsistent information. Even in
debugfs files inconsistency is a pain because it make debugging via mail/
bugzille etc. unnecessarily cumbersome.

Thanks,

tglx