| Message ID | cca1effa488065cb055120aa01b65719094bdcb5.1584530321.git.lukas@wunner.de |
|---|---|
| State | New |
| Headers | show |
| Series | PCI: pciehp: Fix indefinite wait on sysfs requests | expand |
On Wed, Mar 18, 2020 at 12:33:12PM +0100, Lukas Wunner wrote: > Fixes: 54ecb8f7028c ("PCI: pciehp: Avoid returning prematurely from sysfs requests") > Reported-by: David Hoyer <David.Hoyer@netapp.com> > Signed-off-by: Lukas Wunner <lukas@wunner.de> > Cc: stable@vger.kernel.org # v4.19+ > Cc: Keith Busch <kbusch@kernel.org> Looks good to me. Reviewed-by: Keith Busch <kbusch@kernel.org> > drivers/pci/hotplug/pciehp_hpc.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c > index e4627c68b30f..5f1a27bfcb19 100644 > --- a/drivers/pci/hotplug/pciehp_hpc.c > +++ b/drivers/pci/hotplug/pciehp_hpc.c > @@ -663,17 +663,15 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) > 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 */ > @@ -702,10 +700,12 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) > 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) > -- > 2.25.0 >
On Wed, Mar 18, 2020 at 12:33:12PM +0100, Lukas Wunner wrote: > 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 54ecb8f7028c ("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: 54ecb8f7028c ("PCI: pciehp: Avoid returning prematurely from sysfs requests") > Reported-by: David Hoyer <David.Hoyer@netapp.com> > Signed-off-by: Lukas Wunner <lukas@wunner.de> > Cc: stable@vger.kernel.org # v4.19+ > Cc: Keith Busch <kbusch@kernel.org> Applied to pci/hotplug for v5.7, thanks! > --- > drivers/pci/hotplug/pciehp_hpc.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c > index e4627c68b30f..5f1a27bfcb19 100644 > --- a/drivers/pci/hotplug/pciehp_hpc.c > +++ b/drivers/pci/hotplug/pciehp_hpc.c > @@ -663,17 +663,15 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) > 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 */ > @@ -702,10 +700,12 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) > 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) > -- > 2.25.0 >
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c index e4627c68b30f..5f1a27bfcb19 100644 --- a/drivers/pci/hotplug/pciehp_hpc.c +++ b/drivers/pci/hotplug/pciehp_hpc.c @@ -663,17 +663,15 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) 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 */ @@ -702,10 +700,12 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) 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)
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 54ecb8f7028c ("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: 54ecb8f7028c ("PCI: pciehp: Avoid returning prematurely from sysfs requests") Reported-by: David Hoyer <David.Hoyer@netapp.com> Signed-off-by: Lukas Wunner <lukas@wunner.de> Cc: stable@vger.kernel.org # v4.19+ Cc: Keith Busch <kbusch@kernel.org> --- drivers/pci/hotplug/pciehp_hpc.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)