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Date: Tue, 25 Jan 2022 06:23:23 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
Theodore Tso <tytso@....edu>,
Hans de Goede <hdegoede@...hat.com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Lukas Wunner <lukas@...ner.de>
Subject: Re: [PATCH 5.16 0873/1039] PCI: pciehp: Use
down_read/write_nested(reset_lock) to fix lockdep errors
On Mon, Jan 24, 2022 at 07:44:22PM +0100, Greg Kroah-Hartman wrote:
> From: Hans de Goede <hdegoede@...hat.com>
>
> commit 085a9f43433f30cbe8a1ade62d9d7827c3217f4d upstream.
I would hold off on backporting the pciehp changes until we resolve
this regression in v5.17-rc1:
https://bugzilla.kernel.org/show_bug.cgi?id=215525
> 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@....edu>
> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> Reviewed-by: Lukas Wunner <lukas@...ner.de>
> Cc: stable@...r.kernel.org
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
> 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(-)
>
> --- 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;
> --- a/drivers/pci/hotplug/pciehp_core.c
> +++ b/drivers/pci/hotplug/pciehp_core.c
> @@ -166,7 +166,7 @@ static void pciehp_check_presence(struct
> {
> 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);
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -583,7 +583,7 @@ static void pciehp_ignore_dpc_link_chang
> * 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, v
> * 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_slo
> 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 contr
>
> #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
> 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)
>
>
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