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    Subject[PATCH 5.10 461/563] PCI: pciehp: Use down_read/write_nested(reset_lock) to fix lockdep errors
    Date
    From: Hans de Goede <hdegoede@redhat.com>

    commit 085a9f43433f30cbe8a1ade62d9d7827c3217f4d 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>
    ---
    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
    @@ -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;
    --- 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))
    @@ -880,7 +880,7 @@ 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;
    @@ -936,6 +936,20 @@ 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;
    @@ -949,6 +963,7 @@ 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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