linux-kernel - [Patch v1 2/3] PCI: prevent work_on_cpu's probe to execute on isolated CPUs

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Date:   Wed, 10 Jun 2020 12:12:25 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        frederic@...nel.org, mtosatti@...hat.com, juri.lelli@...hat.com,
        abelits@...vell.com, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, rostedt@...dmis.org, mingo@...nel.org,
        peterz@...radead.org, tglx@...utronix.de
Subject: [Patch v1 2/3] PCI: prevent work_on_cpu's probe to execute on isolated CPUs

From: Alex Belits <abelits@...vell.com>

pci_call_probe() prevents the nesting of work_on_cpu()
for a scenario where a VF device is probed from work_on_cpu()
of the Physical device.
This patch replaces the cpumask used in pci_call_probe()
from all online CPUs to only housekeeping CPUs. This is to
ensure that there are no additional latency overheads
caused due to the pinning of jobs on isolated CPUs.

Signed-off-by: Alex Belits <abelits@...vell.com>
Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
---
 drivers/pci/pci-driver.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index da6510af1221..449466f71040 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -12,6 +12,7 @@
 #include <linux/string.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
+#include <linux/sched/isolation.h>
 #include <linux/cpu.h>
 #include <linux/pm_runtime.h>
 #include <linux/suspend.h>
@@ -333,6 +334,7 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
 			  const struct pci_device_id *id)
 {
 	int error, node, cpu;
+	int hk_flags = HK_FLAG_DOMAIN | HK_FLAG_WQ;
 	struct drv_dev_and_id ddi = { drv, dev, id };
 
 	/*
@@ -353,7 +355,8 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
 	    pci_physfn_is_probed(dev))
 		cpu = nr_cpu_ids;
 	else
-		cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
+		cpu = cpumask_any_and(cpumask_of_node(node),
+				      housekeeping_cpumask(hk_flags));
 
 	if (cpu < nr_cpu_ids)
 		error = work_on_cpu(cpu, local_pci_probe, &ddi);
-- 
2.18.4