linux-kernel - Re: [RFC PATCH 05/11] drivers/acpi: convert seqno counter

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Date:   Thu, 24 Sep 2020 13:13:21 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 05/11] drivers/acpi: convert seqno counter_atomic

On Wed, Sep 23, 2020 at 3:44 AM Shuah Khan <skhan@...uxfoundation.org> wrote:
>
> counter_atomic is introduced to be used when a variable is used as
> a simple counter and doesn't guard object lifetimes. This clearly
> differentiates atomic_t usages that guard object lifetimes.
>
> counter_atomic variables will wrap around to 0 when it overflows and
> should not be used to guard resource lifetimes, device usage and
> open counts that control state changes, and pm states.
>
> seqno is a sequence number counter for logging. This counter gets
> incremented. Unsure if there is a chance of this overflowing. It
> doesn't look like overflowing causes any problems since it is used
> to tag the log messages and nothing more.
>
> Convert it to use counter_atomic.
>
> This conversion doesn't change the oveflow wrap around behavior.
>
> Signed-off-by: Shuah Khan <skhan@...uxfoundation.org>

Both this change and the next patch are fine by me.

Thanks!

> ---
>  drivers/acpi/acpi_extlog.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/acpi_extlog.c b/drivers/acpi/acpi_extlog.c
> index f138e12b7b82..23b696b7eb14 100644
> --- a/drivers/acpi/acpi_extlog.c
> +++ b/drivers/acpi/acpi_extlog.c
> @@ -12,6 +12,7 @@
>  #include <linux/ratelimit.h>
>  #include <linux/edac.h>
>  #include <linux/ras.h>
> +#include <linux/counters.h>
>  #include <asm/cpu.h>
>  #include <asm/mce.h>
>
> @@ -93,7 +94,7 @@ static struct acpi_hest_generic_status *extlog_elog_entry_check(int cpu, int ban
>  static void __print_extlog_rcd(const char *pfx,
>                                struct acpi_hest_generic_status *estatus, int cpu)
>  {
> -       static atomic_t seqno;
> +       static struct counter_atomic seqno;
>         unsigned int curr_seqno;
>         char pfx_seq[64];
>
> @@ -103,7 +104,7 @@ static void __print_extlog_rcd(const char *pfx,
>                 else
>                         pfx = KERN_ERR;
>         }
> -       curr_seqno = atomic_inc_return(&seqno);
> +       curr_seqno = counter_atomic_inc_return(&seqno);
>         snprintf(pfx_seq, sizeof(pfx_seq), "%s{%u}", pfx, curr_seqno);
>         printk("%s""Hardware error detected on CPU%d\n", pfx_seq, cpu);
>         cper_estatus_print(pfx_seq, estatus);
> --
> 2.25.1
>