From: Lukas Wunner lukas@wunner.de
commit 3e487d2e4aa466decd226353755c9d423e8fbacc upstream.
David Hoyer reports that powering pciehp slots up or down via sysfs may hang: The call to wait_event() in pciehp_sysfs_enable_slot() and _disable_slot() does not return because ctrl->ist_running remains true.
This flag, which was introduced by commit 157c1062fcd8 ("PCI: pciehp: Avoid returning prematurely from sysfs requests"), signifies that the IRQ thread pciehp_ist() is running. It is set to true at the top of pciehp_ist() and reset to false at the end. However there are two additional return statements in pciehp_ist() before which the commit neglected to reset the flag to false and wake up waiters for the flag.
That omission opens up the following race when powering up the slot:
* pciehp_ist() runs because a PCI_EXP_SLTSTA_PDC event was requested by pciehp_sysfs_enable_slot()
* pciehp_ist() turns on slot power via the following call stack: pciehp_handle_presence_or_link_change() -> pciehp_enable_slot() -> __pciehp_enable_slot() -> board_added() -> pciehp_power_on_slot()
* after slot power is turned on, the link comes up, resulting in a PCI_EXP_SLTSTA_DLLSC event
* the IRQ handler pciehp_isr() stores the event in ctrl->pending_events and returns IRQ_WAKE_THREAD
* the IRQ thread is already woken (it's bringing up the slot), but the genirq code remembers to re-run the IRQ thread after it has finished (such that it can deal with the new event) by setting IRQTF_RUNTHREAD via __handle_irq_event_percpu() -> __irq_wake_thread()
* the IRQ thread removes PCI_EXP_SLTSTA_DLLSC from ctrl->pending_events via board_added() -> pciehp_check_link_status() in order to deal with presence and link flaps per commit 6c35a1ac3da6 ("PCI: pciehp: Tolerate initially unstable link")
* after pciehp_ist() has successfully brought up the slot, it resets ctrl->ist_running to false and wakes up the sysfs requester
* the genirq code re-runs pciehp_ist(), which sets ctrl->ist_running to true but then returns with IRQ_NONE because ctrl->pending_events is empty
* pciehp_sysfs_enable_slot() is finally woken but notices that ctrl->ist_running is true, hence continues waiting
The only way to get the hung task going again is to trigger a hotplug event which brings down the slot, e.g. by yanking out the card.
The same race exists when powering down the slot because remove_board() likewise clears link or presence changes in ctrl->pending_events per commit 3943af9d01e9 ("PCI: pciehp: Ignore Link State Changes after powering off a slot") and thereby may cause a re-run of pciehp_ist() which returns with IRQ_NONE without resetting ctrl->ist_running to false.
Fix by adding a goto label before the teardown steps at the end of pciehp_ist() and jumping to that label from the two return statements which currently neglect to reset the ctrl->ist_running flag.
Fixes: 157c1062fcd8 ("PCI: pciehp: Avoid returning prematurely from sysfs requests") Link: https://lore.kernel.org/r/cca1effa488065cb055120aa01b65719094bdcb5.158453032... Reported-by: David Hoyer David.Hoyer@netapp.com Signed-off-by: Lukas Wunner lukas@wunner.de Signed-off-by: Bjorn Helgaas bhelgaas@google.com Reviewed-by: Keith Busch kbusch@kernel.org Cc: stable@vger.kernel.org # v4.19+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/pci/hotplug/pciehp_hpc.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
--- a/drivers/pci/hotplug/pciehp_hpc.c +++ b/drivers/pci/hotplug/pciehp_hpc.c @@ -625,17 +625,15 @@ static irqreturn_t pciehp_ist(int irq, v if (atomic_fetch_and(~RERUN_ISR, &ctrl->pending_events) & RERUN_ISR) { ret = pciehp_isr(irq, dev_id); enable_irq(irq); - if (ret != IRQ_WAKE_THREAD) { - pci_config_pm_runtime_put(pdev); - return ret; - } + if (ret != IRQ_WAKE_THREAD) + goto out; }
synchronize_hardirq(irq); events = atomic_xchg(&ctrl->pending_events, 0); if (!events) { - pci_config_pm_runtime_put(pdev); - return IRQ_NONE; + ret = IRQ_NONE; + goto out; }
/* Check Attention Button Pressed */ @@ -664,10 +662,12 @@ static irqreturn_t pciehp_ist(int irq, v pciehp_handle_presence_or_link_change(ctrl, events); up_read(&ctrl->reset_lock);
+ ret = IRQ_HANDLED; +out: pci_config_pm_runtime_put(pdev); ctrl->ist_running = false; wake_up(&ctrl->requester); - return IRQ_HANDLED; + return ret; }
static int pciehp_poll(void *data)