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    SubjectRe: [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@redhat.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@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>
    > ---
    > 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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