Re: [PATCH 1/6] x86: mce: no need to check return value of debugfs_create functions

Borislav Petkov
2019-01-22T21:53:31Z

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@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: <x86@kernel.org>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Pu Wen <puwen@hygon.cn>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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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