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

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 (local)
Reported-by: Sargun Dhillon <redacted>
Signed-off-by: Jon Pan-Doh <redacted>
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.
+	 */
  	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",
+					   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);