Re: [PATCH v6 14/16] PCI/AER: Introduce ratelimit for error logs

Ilpo Järvinen
2025-05-20T11:55:43Z

On Mon, 19 May 2025, Bjorn Helgaas wrote:

> From: Jon Pan-Doh <pandoh@google.com>
>
> Spammy devices can flood kernel logs with AER errors and slow/stall
> execution. Add per-device ratelimits for AER correctable and uncorrectable
> errors that use the kernel defaults (10 per 5s).
>
> There are two AER logging entry points:
>
> - aer_print_error() is used by DPC and native AER
>
> - pci_print_aer() is used by GHES and CXL
>
> The native AER aer_print_error() case includes a loop that may log details
> from multiple devices. This is ratelimited by the union of ratelimits for
> these devices, set by add_error_device(), which collects the devices. If
> no such device is found, the Error Source message is ratelimited by the
> Root Port or RCEC that received the ERR_* message.
>
> The DPC aer_print_error() case is currently not ratelimited.
>
> The GHES and CXL pci_print_aer() cases are ratelimited by the Error Source
> device.
>
> Sargun at Meta reported internally that a flood of AER errors causes RCU
> CPU stall warnings and CSD-lock warnings.
>
> Tested using aer-inject[1]. Sent 11 AER errors. Observed 10 errors logged
> while AER stats (cat /sys/bus/pci/devices/<dev>/aer_dev_correctable) show
> true count of 11.
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/gong.chen/aer-inject.git
>
> [bhelgaas: commit log, factor out trace_aer_event() and aer_print_rp_info()
> changes to previous patches, collect single aer_err_info.ratelimit as union
> of ratelimits of all error source devices]
> Link: https://lore.kernel.org/r/20250321015806.954866-7-pandoh@google.com
> Reported-by: Sargun Dhillon <sargun@meta.com>
> Signed-off-by: Jon Pan-Doh <pandoh@google.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
> drivers/pci/pci.h | 3 ++-
> drivers/pci/pcie/aer.c | 49 ++++++++++++++++++++++++++++++++++++------
> drivers/pci/pcie/dpc.c | 1 +
> 3 files changed, 46 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 705f9ef58acc..65c466279ade 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -593,7 +593,8 @@ struct aer_err_info {
> unsigned int id:16;
>
> unsigned int severity:2; /* 0:NONFATAL | 1:FATAL | 2:COR */
> - unsigned int __pad1:5;
> + unsigned int ratelimit:1; /* 0=skip, 1=print */
> + unsigned int __pad1:4;
> unsigned int multi_error_valid:1;
>
> unsigned int first_error:5;
> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> index da62032bf024..c335e0bb9f51 100644
> --- a/drivers/pci/pcie/aer.c
> +++ b/drivers/pci/pcie/aer.c
> @@ -28,6 +28,7 @@
> #include <linux/interrupt.h>
> #include <linux/delay.h>
> #include <linux/kfifo.h>
> +#include <linux/ratelimit.h>
> #include <linux/slab.h>
> #include <acpi/apei.h>
> #include <acpi/ghes.h>
> @@ -88,6 +89,10 @@ struct aer_report {
> u64 rootport_total_cor_errs;
> u64 rootport_total_fatal_errs;
> u64 rootport_total_nonfatal_errs;
> +
> + /* Ratelimits for errors */
> + struct ratelimit_state cor_log_ratelimit;
> + struct ratelimit_state uncor_log_ratelimit;
> };
>
> #define AER_LOG_TLP_MASKS (PCI_ERR_UNC_POISON_TLP| \
> @@ -379,6 +384,11 @@ void pci_aer_init(struct pci_dev *dev)
>
> dev->aer_report = kzalloc(sizeof(*dev->aer_report), GFP_KERNEL);
>
> + ratelimit_state_init(&dev->aer_report->cor_log_ratelimit,
> + DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);
> + ratelimit_state_init(&dev->aer_report->uncor_log_ratelimit,
> + DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);
> +
> /*
> * We save/restore PCI_ERR_UNCOR_MASK, PCI_ERR_UNCOR_SEVER,
> * PCI_ERR_COR_MASK, and PCI_ERR_CAP. Root and Root Complex Event
> @@ -672,6 +682,18 @@ static void pci_rootport_aer_stats_incr(struct pci_dev *pdev,
> }
> }
>
> +static int aer_ratelimit(struct pci_dev *dev, unsigned int severity)
> +{
> + struct ratelimit_state *ratelimit;
> +
> + if (severity == AER_CORRECTABLE)
> + ratelimit = &dev->aer_report->cor_log_ratelimit;
> + else
> + ratelimit = &dev->aer_report->uncor_log_ratelimit;
> +
> + return __ratelimit(ratelimit);
> +}
> +
> static void __aer_print_error(struct pci_dev *dev, struct aer_err_info *info)
> {
> const char **strings;
> @@ -715,6 +737,9 @@ void aer_print_error(struct pci_dev *dev, struct aer_err_info *info)
>
> pci_dev_aer_stats_incr(dev, info);
>
> + if (!info->ratelimit)
> + return;
> +
> if (!info->status) {
> pci_err(dev, "PCIe Bus Error: severity=%s, type=Inaccessible, (Unregistered Agent ID)\n",
> aer_error_severity_string[info->severity]);
> @@ -785,6 +810,9 @@ void pci_print_aer(struct pci_dev *dev, int aer_severity,
>
> pci_dev_aer_stats_incr(dev, &info);
>
> + if (!aer_ratelimit(dev, info.severity))
> + return;
> +
> layer = AER_GET_LAYER_ERROR(aer_severity, status);
> agent = AER_GET_AGENT(aer_severity, status);
>
> @@ -815,8 +843,14 @@ EXPORT_SYMBOL_NS_GPL(pci_print_aer, "CXL");
> */
> static int add_error_device(struct aer_err_info *e_info, struct pci_dev *dev)
> {
> + /*
> + * Ratelimit AER log messages. Generally we add the Error Source
> + * device, but there are is_error_source() cases that can result in
> + * multiple devices being added here, so we OR them all together.

I can see the code uses OR ;-) but I wasn't helpful because this comment
didn't explain why at all. As this ratelimit thing is using reverse logic
to begin with, this is a very tricky bit.

Perhaps something less vague like:

... we ratelimit if all devices have reached their ratelimit.

Assuming that was the intention here? (I'm not sure.)

> + */
> if (e_info->error_dev_num < AER_MAX_MULTI_ERR_DEVICES) {
> e_info->dev[e_info->error_dev_num] = pci_dev_get(dev);
> + e_info->ratelimit |= aer_ratelimit(dev, e_info->severity);
> e_info->error_dev_num++;
> return 0;
> }
> @@ -914,7 +948,7 @@ static int find_device_iter(struct pci_dev *dev, void *data)
> * e_info->error_dev_num and e_info->dev[], based on the given information.
> */
> static bool find_source_device(struct pci_dev *parent,
> - struct aer_err_info *e_info)
> + struct aer_err_info *e_info)
> {
> struct pci_dev *dev = parent;
> int result;
> @@ -935,10 +969,12 @@ static bool find_source_device(struct pci_dev *parent,
> /*
> * If we didn't find any devices with errors logged in the AER
> * Capability, just print the Error Source ID from the Root Port or
> - * RCEC that received an ERR_* Message.
> + * RCEC that received an ERR_* Message, ratelimited by the RP or
> + * RCEC.
> */
> if (!e_info->error_dev_num) {
> - aer_print_source(parent, e_info, " (no details found)");
> + if (aer_ratelimit(parent, e_info->severity))
> + aer_print_source(parent, e_info, " (no details found)");
> return false;
> }
> return true;
> @@ -1147,9 +1183,10 @@ static void aer_recover_work_func(struct work_struct *work)
> pdev = pci_get_domain_bus_and_slot(entry.domain, entry.bus,
> entry.devfn);
> if (!pdev) {
> - pr_err("no pci_dev for %04x:%02x:%02x.%x\n",
> - entry.domain, entry.bus,
> - PCI_SLOT(entry.devfn), PCI_FUNC(entry.devfn));
> + pr_err_ratelimited("%04x:%02x:%02x.%x: no pci_dev found\n",

This case was not mentioned in the changelog.

> + entry.domain, entry.bus,
> + PCI_SLOT(entry.devfn),
> + PCI_FUNC(entry.devfn));
> continue;
> }
> pci_print_aer(pdev, entry.severity, entry.regs);
> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> index 34af0ea45c0d..597df7790f36 100644
> --- a/drivers/pci/pcie/dpc.c
> +++ b/drivers/pci/pcie/dpc.c
> @@ -301,6 +301,7 @@ void dpc_process_error(struct pci_dev *pdev)
> else if (reason == PCI_EXP_DPC_STATUS_TRIGGER_RSN_UNCOR &&
> dpc_get_aer_uncorrect_severity(pdev, &info) &&
> aer_get_device_error_info(pdev, &info)) {
> + info.ratelimit = 1; /* no ratelimiting */
> aer_print_error(pdev, &info);
> pci_aer_clear_nonfatal_status(pdev);
> pci_aer_clear_fatal_status(pdev);
>

--
i.