linux-kernel - Re: [PATCH v6 2/2] acpi: apei: Do not panic() on PCIe errors reported through GHES

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Date:   Tue, 22 May 2018 11:02:16 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Alexandru Gagniuc <mr.nuke.me@...il.com>
Cc:     Borislav Petkov <bp@...en8.de>, alex_gagniuc@...lteam.com,
        austin_bolen@...l.com, shyam_iyer@...l.com,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Tyler Baicar <tbaicar@...eaurora.org>,
        Will Deacon <will.deacon@....com>,
        James Morse <james.morse@....com>,
        Shiju Jose <shiju.jose@...wei.com>,
        "Jonathan (Zhixiong) Zhang" <zjzhang@...eaurora.org>,
        Dongjiu Geng <gengdongjiu@...wei.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 2/2] acpi: apei: Do not panic() on PCIe errors reported
 through GHES

On Mon, May 21, 2018 at 3:49 PM, Alexandru Gagniuc <mr.nuke.me@...il.com> wrote:
> The policy was to panic() when GHES said that an error is "Fatal".
> This logic is wrong for several reasons, as it doesn't account for the
> cause of the error.
>
> PCIe fatal errors indicate that the link to a device is either
> unstable or unusable. They don't indicate that the machine is on fire,

But they very well may indicate just that AFAICS.

> and they are not severe enough to justify a panic(). Do not blindly
> rely on firmware to evaluate the severity for us. Instead, look at
> the error severity based on what caused the error (GHES subsections).

Which bit also comes from the firmware, right?  So why is it regarded
as a better source of information?

Or are you trying to say that both of the pieces of information in
question should be consistent with each other?  But if they aren't,
which one should we trust more and why?

> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
> ---
>  drivers/acpi/apei/ghes.c | 48 +++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 45 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 7c1a16b106ba..9baaab798020 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -425,8 +425,7 @@ static void ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata, int
>   * GHES_SEV_RECOVERABLE -> AER_NONFATAL
>   * GHES_SEV_RECOVERABLE && CPER_SEC_RESET -> AER_FATAL
>   *     These both need to be reported and recovered from by the AER driver.
> - * GHES_SEV_PANIC does not make it to this handling since the kernel must
> - *     panic.
> + * GHES_SEV_PANIC -> AER_FATAL
>   */
>  static void ghes_handle_aer(struct acpi_hest_generic_data *gdata)
>  {
> @@ -459,6 +458,49 @@ static void ghes_handle_aer(struct acpi_hest_generic_data *gdata)
>  #endif
>  }
>
> +/* PCIe errors should not cause a panic. */

This comment is not sufficient and it should go inside of the function.

> +static int ghes_sec_pcie_severity(struct acpi_hest_generic_data *gdata)
> +{
> +       struct cper_sec_pcie *pcie_err = acpi_hest_get_payload(gdata);
> +
> +       if (pcie_err->validation_bits & CPER_PCIE_VALID_DEVICE_ID &&
> +           pcie_err->validation_bits & CPER_PCIE_VALID_AER_INFO &&
> +           IS_ENABLED(CONFIG_ACPI_APEI_PCIEAER))
> +               return GHES_SEV_RECOVERABLE;

You have not explained convincingly enough why the above condition
makes sense at all.

> +
> +       return ghes_cper_severity(gdata->error_severity);
> +}
> +
> +/*
> + * The severity field in the status block is an unreliable metric for the
> + * severity. A more reliable way is to look at each subsection and see how safe
> + * it is to call the approproate error handler.
> + * We're not conerned with handling the error. We're concerned with being able
> + * to notify an error handler by crossing the NMI/IRQ boundary, being able to
> + * schedule_work, and so forth.
> + *   - SEC_PCIE: All PCIe errors can be handled by AER.

Make this comment a proper kerneldoc or move it inside of the function.

> + */
> +static int ghes_severity(struct ghes *ghes)
> +{
> +       int worst_sev, sec_sev;
> +       struct acpi_hest_generic_data *gdata;
> +       const guid_t *section_type;
> +       const struct acpi_hest_generic_status *estatus = ghes->estatus;
> +
> +       worst_sev = GHES_SEV_NO;
> +       apei_estatus_for_each_section(estatus, gdata) {
> +               section_type = (guid_t *)gdata->section_type;
> +               sec_sev = ghes_cper_severity(gdata->error_severity);
> +
> +               if (guid_equal(section_type, &CPER_SEC_PCIE))
> +                       sec_sev = ghes_sec_pcie_severity(gdata);
> +
> +               worst_sev = max(worst_sev, sec_sev);
> +       }
> +
> +       return worst_sev;
> +}
> +
>  static void ghes_do_proc(struct ghes *ghes,
>                          const struct acpi_hest_generic_status *estatus)
>  {
> @@ -944,7 +986,7 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
>                         ret = NMI_HANDLED;
>                 }
>
> -               sev = ghes_cper_severity(ghes->estatus->error_severity);
> +               sev = ghes_severity(ghes);
>                 if (sev >= GHES_SEV_PANIC) {
>                         oops_begin();
>                         ghes_print_queued_estatus();
> --