linux-kernel - [PATCH] [RESEND] x86/smpboot: avoid warning messages while hot-removing physical cpu

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Message-ID: <de21ed2c-2efe-87be-01ca-a613c78c1027@gmail.com>
Date:   Mon, 5 Feb 2018 08:51:50 -0500
From:   Masayoshi Mizuma <msys.mizuma@...il.com>
To:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] [RESEND] x86/smpboot: avoid warning messages while
 hot-removing physical cpu

From: Masayoshi Mizuma <m.mizuma@...fujitsu.com>

When a physical cpu is hot-removed, the following warning message
are shown while the uncore device is removing in uncore_pci_remove().

WARNING: CPU: 120 PID: 5 at arch/x86/events/intel/uncore.c:988
uncore_pci_remove+0xf1/0x110
...
CPU: 120 PID: 5 Comm: kworker/u1024:0 Not tainted 4.15.0-rc8 #1
Workqueue: kacpi_hotplug acpi_hotplug_work_fn
...
Call Trace:
pci_device_remove+0x36/0xb0
device_release_driver_internal+0x145/0x210
pci_stop_bus_device+0x76/0xa0
pci_stop_root_bus+0x44/0x60
acpi_pci_root_remove+0x1f/0x80
acpi_bus_trim+0x54/0x90
acpi_bus_trim+0x2e/0x90
acpi_device_hotplug+0x2bc/0x4b0
acpi_hotplug_work_fn+0x1a/0x30
process_one_work+0x141/0x340
worker_thread+0x47/0x3e0
kthread+0xf5/0x130

When uncore_pci_remove() runs, it tries to get package id to
clear the value of uncore_extra_pci_dev[].dev[] by using
topology_phys_to_logical_pkg(). The warning messesage are
shown because topology_phys_to_logical_pkg() returns -1.

  arch/x86/events/intel/uncore.c:
  static void uncore_pci_remove(struct pci_dev *pdev)
  {
  ...
          phys_id = uncore_pcibus_to_physid(pdev->bus);
  ...
                  pkg = topology_phys_to_logical_pkg(phys_id); //returns -1
                  for (i = 0; i < UNCORE_EXTRA_PCI_DEV_MAX; i++) {
                          if (uncore_extra_pci_dev[pkg].dev[i] == pdev) {
                                  uncore_extra_pci_dev[pkg].dev[i] = NULL;
                                  break;
                          }
                  }
                  WARN_ON_ONCE(i >= UNCORE_EXTRA_PCI_DEV_MAX); //HERE!!

topology_phys_to_logical_pkg() tries to find
cpuinfo_x86->phys_proc_id that matches the phys_pkg argument.

  arch/x86/kernel/smpboot.c:
  int topology_phys_to_logical_pkg(unsigned int phys_pkg)
  {
          int cpu;

          for_each_possible_cpu(cpu) {
                  struct cpuinfo_x86 *c = &cpu_data(cpu);

                  if (c->initialized && c->phys_proc_id == phys_pkg)
                          return c->logical_proc_id;
          }
          return -1;
  }

However, the phys_proc_id is already set to 0 by remove_siblinginfo()
when the cpu was offlined.
So, topology_phys_to_logical_pkg() cannot find correct the
logical_proc_id and always returns -1.
As the result, uncore_pci_remove() calls WARN_ON_ONCE() and the warning
messages are shown.

To avoid this, remove the setting from remove_siblinginfo().
There is no influence about the removing because phys_proc_id is not
used after it is hot-removed and it is re-set while hot-addeding.

Signed-off-by: Masayoshi Mizuma <m.mizuma@...fujitsu.com>

---
 arch/x86/kernel/smpboot.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ed556d5..844279c 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1431,7 +1431,6 @@ static void remove_siblinginfo(int cpu)
 	cpumask_clear(cpu_llc_shared_mask(cpu));
 	cpumask_clear(topology_sibling_cpumask(cpu));
 	cpumask_clear(topology_core_cpumask(cpu));
-	c->phys_proc_id = 0;
 	c->cpu_core_id = 0;
 	cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
 	recompute_smt_state();
-- 
1.8.3.1

- Masayoshi