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PCI: pciehp: Use down_read/write_nested(reset_lock) to fix lockdep errors

Browse source 
commit 085a9f4343 upstream.

Use down_read_nested() and down_write_nested() when taking the
ctrl->reset_lock rw-sem, passing the number of PCIe hotplug controllers in
the path to the PCI root bus as lock subclass parameter.

This fixes the following false-positive lockdep report when unplugging a
Lenovo X1C8 from a Lenovo 2nd gen TB3 dock:

  pcieport 0000:06:01.0: pciehp: Slot(1): Link Down
  pcieport 0000:06:01.0: pciehp: Slot(1): Card not present
  ============================================
  WARNING: possible recursive locking detected
  5.16.0-rc2+ #621 Not tainted
  --------------------------------------------
  irq/124-pciehp/86 is trying to acquire lock:
  ffff8e5ac4299ef8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_check_presence+0x23/0x80

  but task is already holding lock:
  ffff8e5ac4298af8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_ist+0xf3/0x180

   other info that might help us debug this:
   Possible unsafe locking scenario:

	 CPU0
	 ----
    lock(&ctrl->reset_lock);
    lock(&ctrl->reset_lock);

   *** DEADLOCK ***

   May be due to missing lock nesting notation

  3 locks held by irq/124-pciehp/86:
   #0: ffff8e5ac4298af8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_ist+0xf3/0x180
   #1: ffffffffa3b024e8 (pci_rescan_remove_lock){+.+.}-{3:3}, at: pciehp_unconfigure_device+0x31/0x110
   #2: ffff8e5ac1ee2248 (&dev->mutex){....}-{3:3}, at: device_release_driver+0x1c/0x40

  stack backtrace:
  CPU: 4 PID: 86 Comm: irq/124-pciehp Not tainted 5.16.0-rc2+ #621
  Hardware name: LENOVO 20U90SIT19/20U90SIT19, BIOS N2WET30W (1.20 ) 08/26/2021
  Call Trace:
   <TASK>
   dump_stack_lvl+0x59/0x73
   __lock_acquire.cold+0xc5/0x2c6
   lock_acquire+0xb5/0x2b0
   down_read+0x3e/0x50
   pciehp_check_presence+0x23/0x80
   pciehp_runtime_resume+0x5c/0xa0
   device_for_each_child+0x45/0x70
   pcie_port_device_runtime_resume+0x20/0x30
   pci_pm_runtime_resume+0xa7/0xc0
   __rpm_callback+0x41/0x110
   rpm_callback+0x59/0x70
   rpm_resume+0x512/0x7b0
   __pm_runtime_resume+0x4a/0x90
   __device_release_driver+0x28/0x240
   device_release_driver+0x26/0x40
   pci_stop_bus_device+0x68/0x90
   pci_stop_bus_device+0x2c/0x90
   pci_stop_and_remove_bus_device+0xe/0x20
   pciehp_unconfigure_device+0x6c/0x110
   pciehp_disable_slot+0x5b/0xe0
   pciehp_handle_presence_or_link_change+0xc3/0x2f0
   pciehp_ist+0x179/0x180

This lockdep warning is triggered because with Thunderbolt, hotplug ports
are nested. When removing multiple devices in a daisy-chain, each hotplug
port's reset_lock may be acquired recursively. It's never the same lock, so
the lockdep splat is a false positive.

Because locks at the same hierarchy level are never acquired recursively, a
per-level lockdep class is sufficient to fix the lockdep warning.

The choice to use one lockdep subclass per pcie-hotplug controller in the
path to the root-bus was made to conserve class keys because their number
is limited and the complexity grows quadratically with number of keys
according to Documentation/locking/lockdep-design.rst.

Link: https://lore.kernel.org/linux-pci/20190402021933.GA2966@mit.edu/
Link: https://lore.kernel.org/linux-pci/de684a28-9038-8fc6-27ca-3f6f2f6400d7@redhat.com/
Link: https://lore.kernel.org/r/20211217141709.379663-1-hdegoede@redhat.com
Link: https://bugzilla.kernel.org/show_bug.cgi?id=208855
Reported-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Hans de Goede 2021-12-17 15:17:09 +01:00 • committed by Greg Kroah-Hartman
commit def2825b09
3 changed files with 22 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

3
drivers/pci/hotplug/pciehp.h
View file

@ -72,6 +72,8 @@ extern int pciehp_poll_time;
* @reset_lock: prevents access to the Data Link Layer Link Active bit in the
* Link Status register and to the Presence Detect State bit in the Slot
* Status register during a slot reset which may cause them to flap
* @depth: Number of additional hotplug ports in the path to the root bus,
* used as lock subclass for @reset_lock
* @ist_running: flag to keep user request waiting while IRQ thread is running
* @request_result: result of last user request submitted to the IRQ thread
* @requester: wait queue to wake up on completion of user request,
@ -103,6 +105,7 @@ struct controller {
struct hotplug_slot hotplug_slot; /* hotplug core interface */
struct rw_semaphore reset_lock;
unsigned int depth;
unsigned int ist_running;
int request_result;
wait_queue_head_t requester;

2
drivers/pci/hotplug/pciehp_core.c
View file

@ -166,7 +166,7 @@ static void pciehp_check_presence(struct controller *ctrl)
{
int occupied;
down_read(&ctrl->reset_lock);
down_read_nested(&ctrl->reset_lock, ctrl->depth);
mutex_lock(&ctrl->state_lock);
occupied = pciehp_card_present_or_link_active(ctrl);

21
drivers/pci/hotplug/pciehp_hpc.c
View file

@ -583,7 +583,7 @@ static void pciehp_ignore_dpc_link_change(struct controller *ctrl,
* the corresponding link change may have been ignored above.
* Synthesize it to ensure that it is acted on.
*/
down_read(&ctrl->reset_lock);
down_read_nested(&ctrl->reset_lock, ctrl->depth);
if (!pciehp_check_link_active(ctrl))
pciehp_request(ctrl, PCI_EXP_SLTSTA_DLLSC);
up_read(&ctrl->reset_lock);
@ -746,7 +746,7 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
* Disable requests have higher priority than Presence Detect Changed
* or Data Link Layer State Changed events.
*/
down_read(&ctrl->reset_lock);
down_read_nested(&ctrl->reset_lock, ctrl->depth);
if (events & DISABLE_SLOT)
pciehp_handle_disable_request(ctrl);
else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC))
@ -880,7 +880,7 @@ int pciehp_reset_slot(struct hotplug_slot *hotplug_slot, int probe)
if (probe)
return 0;
down_write(&ctrl->reset_lock);
down_write_nested(&ctrl->reset_lock, ctrl->depth);
if (!ATTN_BUTTN(ctrl)) {
ctrl_mask |= PCI_EXP_SLTCTL_PDCE;
@ -936,6 +936,20 @@ static inline void dbg_ctrl(struct controller *ctrl)
#define FLAG(x, y) (((x) & (y)) ? '+' : '-')
static inline int pcie_hotplug_depth(struct pci_dev *dev)
{
struct pci_bus *bus = dev->bus;
int depth = 0;
while (bus->parent) {
bus = bus->parent;
if (bus->self && bus->self->is_hotplug_bridge)
depth++;
}
return depth;
}
struct controller *pcie_init(struct pcie_device *dev)
{
struct controller *ctrl;
@ -949,6 +963,7 @@ struct controller *pcie_init(struct pcie_device *dev)
return NULL;
ctrl->pcie = dev;
ctrl->depth = pcie_hotplug_depth(dev->port);
pcie_capability_read_dword(pdev, PCI_EXP_SLTCAP, &slot_cap);
if (pdev->hotplug_user_indicators)