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Re: [PATCH 2/5] x86/intel_rdt: Add diagnostics when writing the schemata file

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On Mon, 18 Sep 2017, Luck, Tony wrote:
> @@ -208,14 +241,19 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
>  	char *tok, *resname;
>  	int closid, ret = 0;
>  
> +	seq_buf_clear(&last_cmd_status);
> +
>  	/* Valid input requires a trailing newline */
> -	if (nbytes == 0 || buf[nbytes - 1] != '\n')
> +	if (nbytes == 0 || buf[nbytes - 1] != '\n') {
> +		seq_buf_puts(&last_cmd_status, "no trailing newline\n");
>  		return -EINVAL;
> +	}
>  	buf[nbytes - 1] = '\0';

In all other instances you access last_cmd_status within the
rdtgroup_kn_lock_live() protected section, which also serializes the show()
function via rdtgroup_mutex. Here you do it outside for obvious reasons,
but that opens a can of evil worms ...

Can you please provide and use two helpers - last_cmd_buf_clear() and
last_cmd_buf_puts() - which both have a
lockdep_assert_held(&rdtgroup_mutex) inside to make sure that we don't end
up with unprotected access accidentally?

Thanks,

	tglx

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[RFC 0/5] x86/intel_rdt: Better diagnostics "Luck, Tony" <tony.luck@intel.com> - 2017-09-19 00:20 +0200
  [PATCH 2/5] x86/intel_rdt: Add diagnostics when writing the schemata file "Luck, Tony" <tony.luck@intel.com> - 2017-09-19 00:20 +0200
    Re: [PATCH 2/5] x86/intel_rdt: Add diagnostics when writing the  schemata file Thomas Gleixner <tglx@linutronix.de> - 2017-09-25 16:10 +0200
      Re: [PATCH 2/5] x86/intel_rdt: Add diagnostics when writing the  schemata file "Luck, Tony" <tony.luck@intel.com> - 2017-09-25 23:40 +0200
        RE: [PATCH 2/5] x86/intel_rdt: Add diagnostics when writing the  schemata file "Luck, Tony" <tony.luck@intel.com> - 2017-09-26 00:20 +0200
        Re: [PATCH 2/5] x86/intel_rdt: Add diagnostics when writing the  schemata file Thomas Gleixner <tglx@linutronix.de> - 2017-09-26 00:20 +0200
  Re: [RFC 0/5] x86/intel_rdt: Better diagnostics Steven Rostedt <rostedt@goodmis.org> - 2017-09-19 03:20 +0200
  [PATCH 6/5] x86/intel_rdt: Add documentation for "info/last_cmd_status" "Luck, Tony" <tony.luck@intel.com> - 2017-09-20 01:20 +0200
  Re: [RFC 0/5] x86/intel_rdt: Better diagnostics Borislav Petkov <bp@suse.de> - 2017-09-21 14:10 +0200

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