A last minute revert in 6.7-final introduced a potential deadlock when enabling ASPM during probe of Qualcomm PCIe controllers as reported by lockdep:

============================================ WARNING: possible recursive locking detected 6.7.0 #40 Not tainted -------------------------------------------- kworker/u16:5/90 is trying to acquire lock: ffffacfa78ced000 (pci_bus_sem){++++}-{3:3}, at: pcie_aspm_pm_state_change+0x58/0xdc

but task is already holding lock: ffffacfa78ced000 (pci_bus_sem){++++}-{3:3}, at: pci_walk_bus+0x34/0xbc

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

CPU0 ---- lock(pci_bus_sem); lock(pci_bus_sem);

*** DEADLOCK ***

Call trace: print_deadlock_bug+0x25c/0x348 __lock_acquire+0x10a4/0x2064 lock_acquire+0x1e8/0x318 down_read+0x60/0x184 pcie_aspm_pm_state_change+0x58/0xdc pci_set_full_power_state+0xa8/0x114 pci_set_power_state+0xc4/0x120 qcom_pcie_enable_aspm+0x1c/0x3c [pcie_qcom] pci_walk_bus+0x64/0xbc qcom_pcie_host_post_init_2_7_0+0x28/0x34 [pcie_qcom]

The deadlock can easily be reproduced on machines like the Lenovo ThinkPad X13s by adding a delay to increase the race window during asynchronous probe where another thread can take a write lock.

Add a new pci_set_power_state_locked() and associated helper functions that can be called with the PCI bus semaphore held to avoid taking the read lock twice.

Fixes: f93e71aea6c6 ("Revert "PCI/ASPM: Remove pcie_aspm_pm_state_change()"") Cc: stable@vger.kernel.org # 6.7 Link: https://lore.kernel.org/r/ZZu0qx2cmn7IwTyQ@hovoldconsulting.com Signed-off-by: Johan Hovold johan+linaro@kernel.org --- drivers/pci/bus.c | 50 +++++++++++------ drivers/pci/controller/dwc/pcie-qcom.c | 2 +- drivers/pci/pci.c | 78 +++++++++++++++++--------- drivers/pci/pci.h | 4 +- drivers/pci/pcie/aspm.c | 13 +++-- include/linux/pci.h | 5 ++ 6 files changed, 102 insertions(+), 50 deletions(-)

diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c index 9c2137dae429..116415f91195 100644 --- a/drivers/pci/bus.c +++ b/drivers/pci/bus.c @@ -386,21 +386,8 @@ void pci_bus_add_devices(const struct pci_bus *bus) } EXPORT_SYMBOL(pci_bus_add_devices);

-/** pci_walk_bus - walk devices on/under bus, calling callback. - * @top bus whose devices should be walked - * @cb callback to be called for each device found - * @userdata arbitrary pointer to be passed to callback. - * - * Walk the given bus, including any bridged devices - * on buses under this bus. Call the provided callback - * on each device found. - * - * We check the return of @cb each time. If it returns anything - * other than 0, we break out. - * - */ -void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), - void *userdata) +static void __pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), + void *userdata, bool locked) { struct pci_dev *dev; struct pci_bus *bus; @@ -408,7 +395,8 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), int retval;

bus = top; - down_read(&pci_bus_sem); + if (!locked) + down_read(&pci_bus_sem); next = top->devices.next; for (;;) { if (next == &bus->devices) { @@ -431,10 +419,38 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), if (retval) break; } - up_read(&pci_bus_sem); + if (!locked) + up_read(&pci_bus_sem); +} + +/** + * pci_walk_bus - walk devices on/under bus, calling callback. + * @top bus whose devices should be walked + * @cb callback to be called for each device found + * @userdata arbitrary pointer to be passed to callback. + * + * Walk the given bus, including any bridged devices + * on buses under this bus. Call the provided callback + * on each device found. + * + * We check the return of @cb each time. If it returns anything + * other than 0, we break out. + * + */ +void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), void *userdata) +{ + __pci_walk_bus(top, cb, userdata, false); } EXPORT_SYMBOL_GPL(pci_walk_bus);

+void pci_walk_bus_locked(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), void *userdata) +{ + lockdep_assert_held(&pci_bus_sem); + + __pci_walk_bus(top, cb, userdata, true); +} +EXPORT_SYMBOL_GPL(pci_walk_bus_locked); + struct pci_bus *pci_bus_get(struct pci_bus *bus) { if (bus) diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c index 10f2d0bb86be..2ce2a3bd932b 100644 --- a/drivers/pci/controller/dwc/pcie-qcom.c +++ b/drivers/pci/controller/dwc/pcie-qcom.c @@ -972,7 +972,7 @@ static int qcom_pcie_enable_aspm(struct pci_dev *pdev, void *userdata) * Downstream devices need to be in D0 state before enabling PCI PM * substates. */ - pci_set_power_state(pdev, PCI_D0); + pci_set_power_state_locked(pdev, PCI_D0); pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);

return 0; diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index d8f11a078924..9ab9b1008d8b 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -1354,6 +1354,7 @@ int pci_power_up(struct pci_dev *dev) /** * pci_set_full_power_state - Put a PCI device into D0 and update its state * @dev: PCI device to power up + * @locked: whether pci_bus_sem is held * * Call pci_power_up() to put @dev into D0, read from its PCI_PM_CTRL register * to confirm the state change, restore its BARs if they might be lost and @@ -1363,7 +1364,7 @@ int pci_power_up(struct pci_dev *dev) * to D0, it is more efficient to use pci_power_up() directly instead of this * function. */ -static int pci_set_full_power_state(struct pci_dev *dev) +static int pci_set_full_power_state(struct pci_dev *dev, bool locked) { u16 pmcsr; int ret; @@ -1399,7 +1400,7 @@ static int pci_set_full_power_state(struct pci_dev *dev) }

if (dev->bus->self) - pcie_aspm_pm_state_change(dev->bus->self); + pcie_aspm_pm_state_change(dev->bus->self, locked);

return 0; } @@ -1428,10 +1429,22 @@ void pci_bus_set_current_state(struct pci_bus *bus, pci_power_t state) pci_walk_bus(bus, __pci_dev_set_current_state, &state); }

+static void __pci_bus_set_current_state(struct pci_bus *bus, pci_power_t state, bool locked) +{ + if (!bus) + return; + + if (locked) + pci_walk_bus_locked(bus, __pci_dev_set_current_state, &state); + else + pci_walk_bus(bus, __pci_dev_set_current_state, &state); +} + /** * pci_set_low_power_state - Put a PCI device into a low-power state. * @dev: PCI device to handle. * @state: PCI power state (D1, D2, D3hot) to put the device into. + * @locked: whether pci_bus_sem is held * * Use the device's PCI_PM_CTRL register to put it into a low-power state. * @@ -1442,7 +1455,7 @@ void pci_bus_set_current_state(struct pci_bus *bus, pci_power_t state) * 0 if device already is in the requested state. * 0 if device's power state has been successfully changed. */ -static int pci_set_low_power_state(struct pci_dev *dev, pci_power_t state) +static int pci_set_low_power_state(struct pci_dev *dev, pci_power_t state, bool locked) { u16 pmcsr;

@@ -1496,29 +1509,12 @@ static int pci_set_low_power_state(struct pci_dev *dev, pci_power_t state) pci_power_name(state));

if (dev->bus->self) - pcie_aspm_pm_state_change(dev->bus->self); + pcie_aspm_pm_state_change(dev->bus->self, locked);

return 0; }

-/** - * pci_set_power_state - Set the power state of a PCI device - * @dev: PCI device to handle. - * @state: PCI power state (D0, D1, D2, D3hot) to put the device into. - * - * Transition a device to a new power state, using the platform firmware and/or - * the device's PCI PM registers. - * - * RETURN VALUE: - * -EINVAL if the requested state is invalid. - * -EIO if device does not support PCI PM or its PM capabilities register has a - * wrong version, or device doesn't support the requested state. - * 0 if the transition is to D1 or D2 but D1 and D2 are not supported. - * 0 if device already is in the requested state. - * 0 if the transition is to D3 but D3 is not supported. - * 0 if device's power state has been successfully changed. - */ -int pci_set_power_state(struct pci_dev *dev, pci_power_t state) +static int __pci_set_power_state(struct pci_dev *dev, pci_power_t state, bool locked) { int error;

@@ -1542,7 +1538,7 @@ int pci_set_power_state(struct pci_dev *dev, pci_power_t state) return 0;

if (state == PCI_D0) - return pci_set_full_power_state(dev); + return pci_set_full_power_state(dev, locked);

/* * This device is quirked not to be put into D3, so don't put it in @@ -1556,16 +1552,16 @@ int pci_set_power_state(struct pci_dev *dev, pci_power_t state) * To put the device in D3cold, put it into D3hot in the native * way, then put it into D3cold using platform ops. */ - error = pci_set_low_power_state(dev, PCI_D3hot); + error = pci_set_low_power_state(dev, PCI_D3hot, locked);

if (pci_platform_power_transition(dev, PCI_D3cold)) return error;

/* Powering off a bridge may power off the whole hierarchy */ if (dev->current_state == PCI_D3cold) - pci_bus_set_current_state(dev->subordinate, PCI_D3cold); + __pci_bus_set_current_state(dev->subordinate, PCI_D3cold, locked); } else { - error = pci_set_low_power_state(dev, state); + error = pci_set_low_power_state(dev, state, locked);

if (pci_platform_power_transition(dev, state)) return error; @@ -1573,8 +1569,38 @@ int pci_set_power_state(struct pci_dev *dev, pci_power_t state)

return 0; } + +/** + * pci_set_power_state - Set the power state of a PCI device + * @dev: PCI device to handle. + * @state: PCI power state (D0, D1, D2, D3hot) to put the device into. + * + * Transition a device to a new power state, using the platform firmware and/or + * the device's PCI PM registers. + * + * RETURN VALUE: + * -EINVAL if the requested state is invalid. + * -EIO if device does not support PCI PM or its PM capabilities register has a + * wrong version, or device doesn't support the requested state. + * 0 if the transition is to D1 or D2 but D1 and D2 are not supported. + * 0 if device already is in the requested state. + * 0 if the transition is to D3 but D3 is not supported. + * 0 if device's power state has been successfully changed. + */ +int pci_set_power_state(struct pci_dev *dev, pci_power_t state) +{ + return __pci_set_power_state(dev, state, false); +} EXPORT_SYMBOL(pci_set_power_state);

+int pci_set_power_state_locked(struct pci_dev *dev, pci_power_t state) +{ + lockdep_assert_held(&pci_bus_sem); + + return __pci_set_power_state(dev, state, true); +} +EXPORT_SYMBOL(pci_set_power_state_locked); + #define PCI_EXP_SAVE_REGS 7

static struct pci_cap_saved_state *_pci_find_saved_cap(struct pci_dev *pci_dev, diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h index 2336a8d1edab..e9750b1b19ba 100644 --- a/drivers/pci/pci.h +++ b/drivers/pci/pci.h @@ -571,12 +571,12 @@ int pcie_retrain_link(struct pci_dev *pdev, bool use_lt); #ifdef CONFIG_PCIEASPM void pcie_aspm_init_link_state(struct pci_dev *pdev); void pcie_aspm_exit_link_state(struct pci_dev *pdev); -void pcie_aspm_pm_state_change(struct pci_dev *pdev); +void pcie_aspm_pm_state_change(struct pci_dev *pdev, bool locked); void pcie_aspm_powersave_config_link(struct pci_dev *pdev); #else static inline void pcie_aspm_init_link_state(struct pci_dev *pdev) { } static inline void pcie_aspm_exit_link_state(struct pci_dev *pdev) { } -static inline void pcie_aspm_pm_state_change(struct pci_dev *pdev) { } +static inline void pcie_aspm_pm_state_change(struct pci_dev *pdev, bool locked) { } static inline void pcie_aspm_powersave_config_link(struct pci_dev *pdev) { } #endif

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c index 5a0066ecc3c5..bc0bd86695ec 100644 --- a/drivers/pci/pcie/aspm.c +++ b/drivers/pci/pcie/aspm.c @@ -1003,8 +1003,11 @@ void pcie_aspm_exit_link_state(struct pci_dev *pdev) up_read(&pci_bus_sem); }

-/* @pdev: the root port or switch downstream port */ -void pcie_aspm_pm_state_change(struct pci_dev *pdev) +/* + * @pdev: the root port or switch downstream port + * @locked: whether pci_bus_sem is held + */ +void pcie_aspm_pm_state_change(struct pci_dev *pdev, bool locked) { struct pcie_link_state *link = pdev->link_state;

@@ -1014,12 +1017,14 @@ void pcie_aspm_pm_state_change(struct pci_dev *pdev) * Devices changed PM state, we should recheck if latency * meets all functions' requirement */ - down_read(&pci_bus_sem); + if (!locked) + down_read(&pci_bus_sem); mutex_lock(&aspm_lock); pcie_update_aspm_capable(link->root); pcie_config_aspm_path(link); mutex_unlock(&aspm_lock); - up_read(&pci_bus_sem); + if (!locked) + up_read(&pci_bus_sem); }

void pcie_aspm_powersave_config_link(struct pci_dev *pdev) diff --git a/include/linux/pci.h b/include/linux/pci.h index add9368e6314..7ab0d13672da 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -1422,6 +1422,7 @@ int pci_load_and_free_saved_state(struct pci_dev *dev, struct pci_saved_state **state); int pci_platform_power_transition(struct pci_dev *dev, pci_power_t state); int pci_set_power_state(struct pci_dev *dev, pci_power_t state); +int pci_set_power_state_locked(struct pci_dev *dev, pci_power_t state); pci_power_t pci_choose_state(struct pci_dev *dev, pm_message_t state); bool pci_pme_capable(struct pci_dev *dev, pci_power_t state); void pci_pme_active(struct pci_dev *dev, bool enable); @@ -1625,6 +1626,8 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,

void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), void *userdata); +void pci_walk_bus_locked(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), + void *userdata); int pci_cfg_space_size(struct pci_dev *dev); unsigned char pci_bus_max_busnr(struct pci_bus *bus); void pci_setup_bridge(struct pci_bus *bus); @@ -2025,6 +2028,8 @@ static inline int pci_save_state(struct pci_dev *dev) { return 0; } static inline void pci_restore_state(struct pci_dev *dev) { } static inline int pci_set_power_state(struct pci_dev *dev, pci_power_t state) { return 0; } +static inline int pci_set_power_state_locked(struct pci_dev *dev, pci_power_t state) +{ return 0; } static inline int pci_wake_from_d3(struct pci_dev *dev, bool enable) { return 0; } static inline pci_power_t pci_choose_state(struct pci_dev *dev,