On Fri, Dec 17, 2021 at 03:17:09PM +0100, Hans de Goede wrote:
> 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:
>
> [ 28.583853] pcieport 0000:06:01.0: pciehp: Slot(1): Link Down
> [ 28.583891] pcieport 0000:06:01.0: pciehp: Slot(1): Card not present
> [ 28.584849] ============================================
> [ 28.584854] WARNING: possible recursive locking detected
> [ 28.584858] 5.16.0-rc2+ #621 Not tainted
> [ 28.584864] --------------------------------------------
> [ 28.584867] irq/124-pciehp/86 is trying to acquire lock:
> [ 28.584873] ffff8e5ac4299ef8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_check_presence+0x23/0x80
> [ 28.584904]
> but task is already holding lock:
> [ 28.584908] ffff8e5ac4298af8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_ist+0xf3/0x180
> [ 28.584929]
> other info that might help us debug this:
> [ 28.584933] Possible unsafe locking scenario:
>
> [ 28.584936] CPU0
> [ 28.584939] ----
> [ 28.584942] lock(&ctrl->reset_lock);
> [ 28.584949] lock(&ctrl->reset_lock);
> [ 28.584955]
> *** DEADLOCK ***
>
> [ 28.584959] May be due to missing lock nesting notation
>
> [ 28.584963] 3 locks held by irq/124-pciehp/86:
> [ 28.584970] #0: ffff8e5ac4298af8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_ist+0xf3/0x180
> [ 28.584991] #1: ffffffffa3b024e8 (pci_rescan_remove_lock){+.+.}-{3:3}, at: pciehp_unconfigure_device+0x31/0x110
> [ 28.585012] #2: ffff8e5ac1ee2248 (&dev->mutex){....}-{3:3}, at: device_release_driver+0x1c/0x40
> [ 28.585037]
> stack backtrace:
> [ 28.585042] CPU: 4 PID: 86 Comm: irq/124-pciehp Not tainted 5.16.0-rc2+ #621
> [ 28.585052] Hardware name: LENOVO 20U90SIT19/20U90SIT19, BIOS N2WET30W (1.20 ) 08/26/2021
> [ 28.585059] Call Trace:
> [ 28.585064] <TASK>
> [ 28.585073] dump_stack_lvl+0x59/0x73
> [ 28.585087] __lock_acquire.cold+0xc5/0x2c6
> [ 28.585106] ? find_held_lock+0x2b/0x80
> [ 28.585124] lock_acquire+0xb5/0x2b0
> [ 28.585132] ? pciehp_check_presence+0x23/0x80
> [ 28.585144] ? lock_is_held_type+0xa8/0x120
> [ 28.585161] down_read+0x3e/0x50
> [ 28.585172] ? pciehp_check_presence+0x23/0x80
> [ 28.585183] pciehp_check_presence+0x23/0x80
> [ 28.585194] pciehp_runtime_resume+0x5c/0xa0
> [ 28.585206] ? pci_msix_init+0x60/0x60
> [ 28.585214] device_for_each_child+0x45/0x70
> [ 28.585227] pcie_port_device_runtime_resume+0x20/0x30
> [ 28.585236] pci_pm_runtime_resume+0xa7/0xc0
> [ 28.585246] ? pci_pm_freeze_noirq+0x100/0x100
> [ 28.585257] __rpm_callback+0x41/0x110
> [ 28.585271] ? pci_pm_freeze_noirq+0x100/0x100
> [ 28.585281] rpm_callback+0x59/0x70
> [ 28.585293] rpm_resume+0x512/0x7b0
> [ 28.585309] __pm_runtime_resume+0x4a/0x90
> [ 28.585322] __device_release_driver+0x28/0x240
> [ 28.585338] device_release_driver+0x26/0x40
> [ 28.585351] pci_stop_bus_device+0x68/0x90
> [ 28.585363] pci_stop_bus_device+0x2c/0x90
> [ 28.585373] pci_stop_and_remove_bus_device+0xe/0x20
> [ 28.585384] pciehp_unconfigure_device+0x6c/0x110
> [ 28.585396] ? __pm_runtime_resume+0x58/0x90
> [ 28.585409] pciehp_disable_slot+0x5b/0xe0
> [ 28.585421] pciehp_handle_presence_or_link_change+0xc3/0x2f0
> [ 28.585436] pciehp_ist+0x179/0x180
> [ 28.585449] ? disable_irq_nosync+0x10/0x10
> [ 28.585460] irq_thread_fn+0x1d/0x60
> [ 28.585470] ? irq_thread+0x81/0x1a0
> [ 28.585480] irq_thread+0xcb/0x1a0
> [ 28.585491] ? irq_thread_fn+0x60/0x60
> [ 28.585502] ? irq_thread_check_affinity+0xb0/0xb0
> [ 28.585514] kthread+0x165/0x190
> [ 28.585522] ? set_kthread_struct+0x40/0x40
> [ 28.585531] ret_from_fork+0x1f/0x30
> [ 28.585554] </TASK>
>
> 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@xxxxxxx/
> Link: https://lore.kernel.org/linux-pci/de684a28-9038-8fc6-27ca-3f6f2f6400d7@xxxxxxxxxx/
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: "Theodore Ts'o" <tytso@xxxxxxx>
> Reviewed-by: Lukas Wunner <lukas@xxxxxxxxx>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Applied to pci/hotplug for v5.17, thanks, Hans!
> ---
> Changes in v2:
> - Only use a subclass for each hotplug capable port/parent in the path to
> the PCI root bus, instead of one for each level in the PCI hierarchy,
> to avoid hitting MAX_LOCKDEP_SUBCLASSES
> - Drop the "PCI: Add a pci_dev_depth() helper function" since we now need
> a special version of this to only count hotplug ports
> - Various commit message improvements
> ---
> drivers/pci/hotplug/pciehp.h | 3 +++
> drivers/pci/hotplug/pciehp_core.c | 2 +-
> drivers/pci/hotplug/pciehp_hpc.c | 21 ++++++++++++++++++---
> 3 files changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
> index 918dccbc74b6..e0a614acee05 100644
> --- a/drivers/pci/hotplug/pciehp.h
> +++ b/drivers/pci/hotplug/pciehp.h
> @@ -75,6 +75,8 @@ 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,
> @@ -106,6 +108,7 @@ 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;
> diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
> index f34114d45259..4042d87d539d 100644
> --- a/drivers/pci/hotplug/pciehp_core.c
> +++ b/drivers/pci/hotplug/pciehp_core.c
> @@ -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);
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 83a0fa119cae..963fb50528da 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -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))
> @@ -906,7 +906,7 @@ int pciehp_reset_slot(struct hotplug_slot *hotplug_slot, bool 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;
> @@ -962,6 +962,20 @@ 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;
> @@ -975,6 +989,7 @@ 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)
> --
> 2.33.1
>
