linux/drivers/pci
Thomas Gleixner 1ddd45f8d7 PCI: Use cpu_hotplug_disable() instead of get_online_cpus()
Converting the hotplug locking, i.e. get_online_cpus(), to a percpu rwsem
unearthed a circular lock dependency which was hidden from lockdep due to
the lockdep annotation of get_online_cpus() which prevents lockdep from
creating full dependency chains. There are several variants of this. And
example is:

Chain exists of:

cpu_hotplug_lock.rw_sem --> drm_global_mutex --> &item->mutex

CPU0                    CPU1
----                    ----
lock(&item->mutex);
                        lock(drm_global_mutex);
                        lock(&item->mutex);
lock(cpu_hotplug_lock.rw_sem);

because there are dependencies through workqueues. The call chain is:

	get_online_cpus
	apply_workqueue_attrs
	__alloc_workqueue_key
	ttm_mem_global_init
	ast_ttm_mem_global_init
	drm_global_item_ref
	ast_mm_init
	ast_driver_load
	drm_dev_register
	drm_get_pci_dev
	ast_pci_probe
	local_pci_probe
	work_for_cpu_fn
	process_one_work
	worker_thread

This is not a problem of get_online_cpus() recursion, it's a possible
deadlock undetected by lockdep so far.

The cure is to use cpu_hotplug_disable() instead of get_online_cpus() to
protect the PCI probing.

There is a side effect to this: cpu_hotplug_disable() makes a concurrent
cpu hotplug attempt via the sysfs interfaces fail with -EBUSY, but PCI
probing usually happens during the boot process where no interaction is
possible. Any later invocations are infrequent enough and concurrent
hotplug attempts are so unlikely that the danger of user space visible
regressions is very close to zero. Anyway, thats preferrable over a real
deadlock.


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-pci@vger.kernel.org
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170524081548.691198590@linutronix.de
2017-05-26 10:10:43 +02:00
..
dwc pci-v4.12-changes 2017-05-08 19:03:25 -07:00
endpoint PCI: endpoint: functions: Add an EP function to test PCI 2017-04-11 14:18:37 -05:00
host PCI: Don't allow unbinding host controllers that aren't prepared 2017-04-28 10:38:00 -05:00
hotplug Annotation of module parameters that specify device settings 2017-05-10 19:13:03 -07:00
pcie Merge branch 'pci/enumeration' into next 2017-04-28 10:33:55 -05:00
switch switchtec: Add IOCTLs to the Switchtec driver 2017-04-12 12:23:37 -05:00
Kconfig Merge branch 'pci/switchtec' into next 2017-04-28 10:33:41 -05:00
Makefile Merge branch 'pci/resource-mmap' into next 2017-04-28 10:34:34 -05:00
access.c Merge branch 'pci/misc' into next 2017-04-28 10:34:14 -05:00
ats.c PCI: Remove pci_ats_enabled() 2015-08-13 15:59:59 -05:00
bus.c PCI: Autosense device removal in pci_bridge_d3_update() 2016-11-17 18:44:56 -06:00
ecam.c PCI: ECAM: Map config region with pci_remap_cfgspace() 2017-04-24 13:53:14 -05:00
host-bridge.c cxl: use pcibios_free_controller_deferred() when removing vPHBs 2016-08-22 11:09:33 +10:00
hotplug-pci.c
htirq.c x86/htirq: Use hierarchical irqdomain to manage Hypertransport interrupts 2015-04-24 15:36:50 +02:00
iov.c PCI: Add sysfs sriov_drivers_autoprobe to control VF driver binding 2017-04-20 08:53:51 -05:00
irq.c pci-v4.12-changes 2017-05-08 19:03:25 -07:00
mmap.c PCI: Add I/O BAR support to generic pci_mmap_resource_range() 2017-04-20 08:47:47 -05:00
msi.c pci-v4.12-changes 2017-05-08 19:03:25 -07:00
of.c PCI/MSI: Use of_msi_get_domain instead of open-coded "msi-parent" parsing 2015-10-16 13:07:14 +01:00
pci-acpi.c Merge branch 'pci/pm' into next 2016-12-12 11:25:04 -06:00
pci-driver.c PCI: Use cpu_hotplug_disable() instead of get_online_cpus() 2017-05-26 10:10:43 +02:00
pci-label.c PCI: Fix broken URL for Dell biosdevname 2016-02-29 12:03:19 -06:00
pci-mid.c pci-v4.10-changes 2016-12-15 12:46:48 -08:00
pci-stub.c
pci-sysfs.c Merge branch 'pci/virtualization' into next 2017-04-28 10:36:12 -05:00
pci.c Merge branch 'pci/virtualization' into next 2017-04-28 10:36:12 -05:00
pci.h pci-v4.12-changes 2017-05-08 19:03:25 -07:00
probe.c IOMMU Updates for Linux v4.12 2017-05-09 15:15:47 -07:00
proc.c PCI: Add BAR index argument to pci_mmap_page_range() 2017-04-20 08:47:47 -05:00
quirks.c Merge branch 'pci/virtualization' into next 2017-04-28 10:36:12 -05:00
remove.c PCI: Autosense device removal in pci_bridge_d3_update() 2016-11-17 18:44:56 -06:00
rom.c PCI: Add comments about ROM BAR updating 2016-11-29 18:05:09 -06:00
search.c PCI: Add device flag PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT 2017-04-13 18:49:50 -05:00
setup-bus.c PCI: Fix calculation of bridge window's size and alignment 2017-04-18 14:47:20 -05:00
setup-irq.c PCI: Export symbols required for loadable host driver modules 2015-04-08 14:17:10 -05:00
setup-res.c PCI: Make PCI_ROM_ADDRESS_MASK a 32-bit constant 2017-04-18 14:46:57 -05:00
slot.c locking/atomic, kref: Add kref_read() 2017-01-14 11:37:18 +01:00
syscall.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
vc.c PCI: Fix unaligned accesses in VC code 2016-06-20 13:24:20 -05:00
vpd.c
xen-pcifront.c xen: make use of xenbus_read_unsigned() in xen-pcifront 2016-11-07 13:55:26 +01:00