linux-kernel - Re: [PATCH 1/6] x86: mce: no need to check return value of debugfs

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Date:   Tue, 22 Jan 2019 22:53:26 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
        Tony Luck <tony.luck@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Pu Wen <puwen@...on.cn>
Subject: Re: [PATCH 1/6] x86: mce: no need to check return value of
 debugfs_create functions

On Tue, Jan 22, 2019 at 03:35:37PM +0100, Greg Kroah-Hartman wrote:
> When calling debugfs functions, there is no need to ever check the
> return value.  The function can work or not, but the code logic should
> never do something different based on this.
> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: <x86@...nel.org>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Vishal Verma <vishal.l.verma@...el.com>
> Cc: Pu Wen <puwen@...on.cn>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  arch/x86/kernel/cpu/mce/core.c     | 15 ++++---------
>  arch/x86/kernel/cpu/mce/inject.c   | 34 +++++-------------------------
>  arch/x86/kernel/cpu/mce/severity.c | 14 +++---------
>  3 files changed, 12 insertions(+), 51 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 672c7225cb1b..1f13f9032a8a 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -2457,22 +2457,15 @@ static int fake_panic_set(void *data, u64 val)
>  DEFINE_SIMPLE_ATTRIBUTE(fake_panic_fops, fake_panic_get,
>  			fake_panic_set, "%llu\n");
>  
> -static int __init mcheck_debugfs_init(void)
> +static void __init mcheck_debugfs_init(void)
>  {
> -	struct dentry *dmce, *ffake_panic;
> +	struct dentry *dmce;
>  
>  	dmce = mce_get_debugfs_dir();
> -	if (!dmce)
> -		return -ENOMEM;
> -	ffake_panic = debugfs_create_file("fake_panic", 0444, dmce, NULL,
> -					  &fake_panic_fops);
> -	if (!ffake_panic)
> -		return -ENOMEM;
> -
> -	return 0;
> +	debugfs_create_file("fake_panic", 0444, dmce, NULL, &fake_panic_fops);

Right, for that I don't care if it fails or not...

>  #else
> -static int __init mcheck_debugfs_init(void) { return -EINVAL; }
> +static void __init mcheck_debugfs_init(void) { }
>  #endif
>  
>  DEFINE_STATIC_KEY_FALSE(mcsafe_key);
> diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
> index 8492ef7d9015..0f5b6c57ffde 100644
> --- a/arch/x86/kernel/cpu/mce/inject.c
> +++ b/arch/x86/kernel/cpu/mce/inject.c
> @@ -648,7 +648,6 @@ static const struct file_operations readme_fops = {
>  
>  static struct dfs_node {
>  	char *name;
> -	struct dentry *d;
>  	const struct file_operations *fops;
>  	umode_t perm;
>  } dfs_fls[] = {
> @@ -662,7 +661,7 @@ static struct dfs_node {
>  	{ .name = "README",	.fops = &readme_fops, .perm = S_IRUSR | S_IRGRP | S_IROTH },
>  };
>  
> -static int __init debugfs_init(void)
> +static void __init debugfs_init(void)
>  {
>  	unsigned int i;
>  	u64 cap;
> @@ -671,30 +670,11 @@ static int __init debugfs_init(void)
>  	n_banks = cap & MCG_BANKCNT_MASK;
>  
>  	dfs_inj = debugfs_create_dir("mce-inject", NULL);
> -	if (!dfs_inj)
> -		return -EINVAL;
> -
> -	for (i = 0; i < ARRAY_SIZE(dfs_fls); i++) {
> -		dfs_fls[i].d = debugfs_create_file(dfs_fls[i].name,
> -						    dfs_fls[i].perm,
> -						    dfs_inj,
> -						    &i_mce,
> -						    dfs_fls[i].fops);
> -
> -		if (!dfs_fls[i].d)
> -			goto err_dfs_add;
> -	}
> -
> -	return 0;
>  
> -err_dfs_add:
> -	while (i-- > 0)
> -		debugfs_remove(dfs_fls[i].d);
> +	for (i = 0; i < ARRAY_SIZE(dfs_fls); i++)
> +		debugfs_create_file(dfs_fls[i].name, dfs_fls[i].perm, dfs_inj,
> +				    &i_mce, dfs_fls[i].fops);

... but that matters: if any of those debugfs files cannot be created
for whatever reason, that injector module is useless because I can't
inject MCEs properly.

I mean, I like the simplification but ...

-- 
Regards/Gruss,
    Boris.

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