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Wed, 12 Jun 2024 11:10:41 -0700 Received: from twshared16022.02.ash9.facebook.com (2620:10d:c085:208::11) by mail.thefacebook.com (2620:10d:c08b:78::2ac9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.1544.11; Wed, 12 Jun 2024 18:10:40 +0000 Received: by devbig638.nha1.facebook.com (Postfix, from userid 544533) id 94E9FF5FBC44; Wed, 12 Jun 2024 11:10:25 -0700 (PDT) From: Keith Busch To: , , CC: Keith Busch Subject: [PATCH 1/2] PCI: pciehp: fix concurrent sub-tree removal deadlock Date: Wed, 12 Jun 2024 11:10:23 -0700 Message-ID: <20240612181024.3577119-2-kbusch@meta.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240612181024.3577119-1-kbusch@meta.com> References: <20240612181024.3577119-1-kbusch@meta.com> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-GUID: S2J3V43L-8f6RrKZQ-GvxSoeY778pbnU X-Proofpoint-ORIG-GUID: S2J3V43L-8f6RrKZQ-GvxSoeY778pbnU X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-06-12_09,2024-06-12_02,2024-05-17_01 From: Keith Busch PCIe hotplug events modify the topology in their IRQ thread once it can acquire the global pci_rescan_remove_lock. If a different removal event happens to acquire that lock first, and that removal event is for the parent device of the bridge processing the other hotplug event, then we are deadlocked: the parent removal will wait indefinitely on the child's IRQ thread because the parent is holding the global lock the child thread needs to make forward progress. Introduce a new locking function that aborts if the device is being removed. The following are stack traces of the deadlock: Task A: pciehp_unconfigure_device+0x41/0x120 pciehp_disable_slot+0x3c/0xc0 pciehp_handle_presence_or_link_change+0x28f/0x3e0 pciehp_ist+0xc3/0x210 irq_thread_fn+0x19/0x40 Task B: __synchronize_irq+0x5b/0x90 free_irq+0x192/0x2e0 pcie_shutdown_notification+0x3b/0x40 pciehp_remove+0x23/0x50 pcie_port_remove_service+0x2c/0x40 device_release_driver_internal+0x11f/0x180 bus_remove_device+0xc5/0x110 device_del+0x126/0x340 device_unregister+0x13/0x50 remove_iter+0x17/0x20 device_for_each_child+0x4a/0x70 pcie_portdrv_remove+0x23/0x40 pci_device_remove+0x24/0x60 device_release_driver_internal+0x11f/0x180 pci_stop_bus_device+0x57/0x80 pci_stop_bus_device+0x2c/0x80 pci_stop_and_remove_bus_device+0xe/0x20 pciehp_unconfigure_device+0x76/0x120 pciehp_disable_slot+0x3c/0xc0 pciehp_handle_presence_or_link_change+0x28f/0x3e0 pciehp_ist+0xc3/0x210 irq_thread_fn+0x19/0x40 Signed-off-by: Keith Busch --- drivers/pci/hotplug/pciehp_pci.c | 12 +++++++++--- drivers/pci/pci.h | 1 + drivers/pci/probe.c | 24 ++++++++++++++++++++++++ include/linux/pci.h | 2 ++ 4 files changed, 36 insertions(+), 3 deletions(-) diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c index ad12515a4a121..ca6237b0732c8 100644 --- a/drivers/pci/hotplug/pciehp_pci.c +++ b/drivers/pci/hotplug/pciehp_pci.c @@ -34,9 +34,12 @@ int pciehp_configure_device(struct controller *ctrl) struct pci_dev *dev; struct pci_dev *bridge = ctrl->pcie->port; struct pci_bus *parent = bridge->subordinate; - int num, ret = 0; + int num, ret; - pci_lock_rescan_remove(); + ret = pci_trylock_rescan_remove(bridge); + if (!ret) + return -ENODEV; + ret = 0; dev = pci_get_slot(parent, PCI_DEVFN(0, 0)); if (dev) { @@ -93,6 +96,7 @@ void pciehp_unconfigure_device(struct controller *ctrl, bool presence) struct pci_dev *dev, *temp; struct pci_bus *parent = ctrl->pcie->port->subordinate; u16 command; + int ret; ctrl_dbg(ctrl, "%s: domain:bus:dev = %04x:%02x:00\n", __func__, pci_domain_nr(parent), parent->number); @@ -100,7 +104,9 @@ void pciehp_unconfigure_device(struct controller *ctrl, bool presence) if (!presence) pci_walk_bus(parent, pci_dev_set_disconnected, NULL); - pci_lock_rescan_remove(); + ret = pci_trylock_rescan_remove(parent->self); + if (!ret) + return; /* * Stopping an SR-IOV PF device removes all the associated VFs, diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h index fd44565c47562..f525490a02122 100644 --- a/drivers/pci/pci.h +++ b/drivers/pci/pci.h @@ -370,6 +370,7 @@ static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused) { pci_dev_set_io_state(dev, pci_channel_io_perm_failure); pci_doe_disconnected(dev); + pci_notify_disconnected(); return 0; } diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c index 5fbabb4e3425f..d2e19a1d1a45b 100644 --- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c @@ -3302,6 +3302,7 @@ EXPORT_SYMBOL_GPL(pci_rescan_bus); * routines should always be executed under this mutex. */ static DEFINE_MUTEX(pci_rescan_remove_lock); +static DECLARE_WAIT_QUEUE_HEAD(pci_lock_wq); void pci_lock_rescan_remove(void) { @@ -3309,12 +3310,35 @@ void pci_lock_rescan_remove(void) } EXPORT_SYMBOL_GPL(pci_lock_rescan_remove); +/* + * pci_trylock_rescan_remove() - keep trying to take the lock until successful + * or notified the device is disconnected + * + * Returns 1 if the lock was successfully taken, 0 otherwise. + */ +bool pci_trylock_rescan_remove(struct pci_dev *dev) +{ + int ret; + + wait_event(pci_lock_wq, + (ret = mutex_trylock(&pci_rescan_remove_lock)) == 1 || + pci_dev_is_disconnected(dev)); + + return ret; +} + void pci_unlock_rescan_remove(void) { mutex_unlock(&pci_rescan_remove_lock); + wake_up_all(&pci_lock_wq); } EXPORT_SYMBOL_GPL(pci_unlock_rescan_remove); +void pci_notify_disconnected(void) +{ + wake_up_all(&pci_lock_wq); +} + static int __init pci_sort_bf_cmp(const struct device *d_a, const struct device *d_b) { diff --git a/include/linux/pci.h b/include/linux/pci.h index cafc5ab1cbcb4..b05aaf9aac6c8 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -1442,7 +1442,9 @@ void set_pcie_hotplug_bridge(struct pci_dev *pdev); unsigned int pci_rescan_bus_bridge_resize(struct pci_dev *bridge); unsigned int pci_rescan_bus(struct pci_bus *bus); void pci_lock_rescan_remove(void); +bool pci_trylock_rescan_remove(struct pci_dev *dev); void pci_unlock_rescan_remove(void); +void pci_notify_disconnected(void); /* Vital Product Data routines */ ssize_t pci_read_vpd(struct pci_dev *dev, loff_t pos, size_t count, void *buf);