This is a note to let you know that I've just added the patch titled PCI: pciehp: Avoid returning prematurely from sysfs requests to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: pci-pciehp-avoid-returning-prematurely-from-sysfs-requests.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 157c1062fcd86ade3c674503705033051fd3d401 Mon Sep 17 00:00:00 2001 From: Lukas Wunner <lukas@xxxxxxxxx> Date: Fri, 9 Aug 2019 12:28:43 +0200 Subject: PCI: pciehp: Avoid returning prematurely from sysfs requests From: Lukas Wunner <lukas@xxxxxxxxx> commit 157c1062fcd86ade3c674503705033051fd3d401 upstream. A sysfs request to enable or disable a PCIe hotplug slot should not return before it has been carried out. That is sought to be achieved by waiting until the controller's "pending_events" have been cleared. However the IRQ thread pciehp_ist() clears the "pending_events" before it acts on them. If pciehp_sysfs_enable_slot() / _disable_slot() happen to check the "pending_events" after they have been cleared but while pciehp_ist() is still running, the functions may return prematurely with an incorrect return value. Fix by introducing an "ist_running" flag which must be false before a sysfs request is allowed to return. Fixes: 32a8cef274fe ("PCI: pciehp: Enable/disable exclusively from IRQ thread") Link: https://lore.kernel.org/linux-pci/1562226638-54134-1-git-send-email-wangxiongfeng2@xxxxxxxxxx Link: https://lore.kernel.org/r/4174210466e27eb7e2243dd1d801d5f75baaffd8.1565345211.git.lukas@xxxxxxxxx Reported-and-tested-by: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # v4.19+ Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/pci/hotplug/pciehp.h | 2 ++ drivers/pci/hotplug/pciehp_ctrl.c | 6 ++++-- drivers/pci/hotplug/pciehp_hpc.c | 2 ++ 3 files changed, 8 insertions(+), 2 deletions(-) --- a/drivers/pci/hotplug/pciehp.h +++ b/drivers/pci/hotplug/pciehp.h @@ -72,6 +72,7 @@ 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 + * @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, * used for synchronous slot enable/disable request via sysfs @@ -101,6 +102,7 @@ struct controller { struct hotplug_slot hotplug_slot; /* hotplug core interface */ struct rw_semaphore reset_lock; + unsigned int ist_running; int request_result; wait_queue_head_t requester; }; --- a/drivers/pci/hotplug/pciehp_ctrl.c +++ b/drivers/pci/hotplug/pciehp_ctrl.c @@ -375,7 +375,8 @@ int pciehp_sysfs_enable_slot(struct hotp ctrl->request_result = -ENODEV; pciehp_request(ctrl, PCI_EXP_SLTSTA_PDC); wait_event(ctrl->requester, - !atomic_read(&ctrl->pending_events)); + !atomic_read(&ctrl->pending_events) && + !ctrl->ist_running); return ctrl->request_result; case POWERON_STATE: ctrl_info(ctrl, "Slot(%s): Already in powering on state\n", @@ -408,7 +409,8 @@ int pciehp_sysfs_disable_slot(struct hot mutex_unlock(&ctrl->state_lock); pciehp_request(ctrl, DISABLE_SLOT); wait_event(ctrl->requester, - !atomic_read(&ctrl->pending_events)); + !atomic_read(&ctrl->pending_events) && + !ctrl->ist_running); return ctrl->request_result; case POWEROFF_STATE: ctrl_info(ctrl, "Slot(%s): Already in powering off state\n", --- a/drivers/pci/hotplug/pciehp_hpc.c +++ b/drivers/pci/hotplug/pciehp_hpc.c @@ -583,6 +583,7 @@ static irqreturn_t pciehp_ist(int irq, v irqreturn_t ret; u32 events; + ctrl->ist_running = true; pci_config_pm_runtime_get(pdev); /* rerun pciehp_isr() if the port was inaccessible on interrupt */ @@ -629,6 +630,7 @@ static irqreturn_t pciehp_ist(int irq, v up_read(&ctrl->reset_lock); pci_config_pm_runtime_put(pdev); + ctrl->ist_running = false; wake_up(&ctrl->requester); return IRQ_HANDLED; } Patches currently in stable-queue which might be from lukas@xxxxxxxxx are queue-5.4/pci-pciehp-avoid-returning-prematurely-from-sysfs-requests.patch