If there are more than one PCIe switch with hotplug downstream ports
hot-removing them leads to a following deadlock:
INFO: task irq/126-pciehp:198 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
irq/126-pciehp D 0 198 2 0x80000000
Call Trace:
__schedule+0x2a2/0x880
schedule+0x2c/0x80
schedule_timeout+0x246/0x350
? ttwu_do_activate+0x67/0x90
wait_for_completion+0xb7/0x140
? wake_up_q+0x80/0x80
kthread_stop+0x49/0x110
__free_irq+0x15c/0x2a0
free_irq+0x32/0x70
pcie_shutdown_notification+0x2f/0x50
pciehp_remove+0x27/0x50
pcie_port_remove_service+0x36/0x50
device_release_driver_internal+0x18c/0x250
device_release_driver+0x12/0x20
bus_remove_device+0xec/0x160
device_del+0x13b/0x350
? pcie_port_find_device+0x60/0x60
device_unregister+0x1a/0x60
remove_iter+0x1e/0x30
device_for_each_child+0x56/0x90
pcie_port_device_remove+0x22/0x40
pcie_portdrv_remove+0x20/0x60
pci_device_remove+0x3e/0xc0
device_release_driver_internal+0x18c/0x250
device_release_driver+0x12/0x20
pci_stop_bus_device+0x6f/0x90
pci_stop_bus_device+0x31/0x90
pci_stop_and_remove_bus_device+0x12/0x20
pciehp_unconfigure_device+0x88/0x140
pciehp_disable_slot+0x6a/0x110
pciehp_handle_presence_or_link_change+0x263/0x400
pciehp_ist+0x1c9/0x1d0
? irq_forced_thread_fn+0x80/0x80
irq_thread_fn+0x24/0x60
irq_thread+0xeb/0x190
? irq_thread_fn+0x60/0x60
kthread+0x120/0x140
? irq_thread_check_affinity+0xf0/0xf0
? kthread_park+0x90/0x90
ret_from_fork+0x35/0x40
INFO: task irq/190-pciehp:2288 blocked for more than 120 seconds.
irq/190-pciehp D 0 2288 2 0x80000000
Call Trace:
__schedule+0x2a2/0x880
schedule+0x2c/0x80
schedule_preempt_disabled+0xe/0x10
__mutex_lock.isra.9+0x2e0/0x4d0
? __mutex_lock_slowpath+0x13/0x20
__mutex_lock_slowpath+0x13/0x20
mutex_lock+0x2c/0x30
pci_lock_rescan_remove+0x15/0x20
pciehp_unconfigure_device+0x4d/0x140
pciehp_disable_slot+0x6a/0x110
pciehp_handle_presence_or_link_change+0x263/0x400
pciehp_ist+0x1c9/0x1d0
? irq_forced_thread_fn+0x80/0x80
irq_thread_fn+0x24/0x60
irq_thread+0xeb/0x190
? irq_thread_fn+0x60/0x60
kthread+0x120/0x140
? irq_thread_check_affinity+0xf0/0xf0
? kthread_park+0x90/0x90
ret_from_fork+0x35/0x40
What happens here is that the whole hierarchy is runtime resumed and the
parent PCIe downstream port, who got the hot-remove event, starts
removing devices below it taking pci_lock_rescan_remove() lock. When the
child PCIe port is runtime resumed it calls pciehp_check_presence()
which ends up calling pciehp_card_present() and pciehp_check_link_active().
Both of these read their parts of PCIe config space by calling helper
function pcie_capability_read_word(). Now, this function notices that
the underlying device is already gone and returns PCIBIOS_DEVICE_NOT_FOUND
with the capability value set to 0. When pciehp gets this value it
thinks that its child device is also hot-removed and schedules its IRQ
thread to handle the event.
The deadlock happens when the child's IRQ thread runs and tries to
acquire pci_lock_rescan_remove() which is already taken by the parent
and the parent waits for the child's IRQ thread to finish.
We can prevent this from happening by checking the return value of
pcie_capability_read_word() and if it is PCIBIOS_DEVICE_NOT_FOUND stop
performing any hot-removal activities.
Signed-off-by: Mika Westerberg <[email protected]>
Tested-by: Kai-Heng Feng <[email protected]>
---
Changes from v2 (https://patchwork.kernel.org/patch/11089973/):
* Check for ~0 as well
* Added tag from Kai-Heng
* Always log lnk_status in pciehp_check_link_active()
* I also experimented renaming the two functions to pciehp_card_absent()
and pciehp_check_link_down() but it ended up looking odd because now we
check for !pciehp_card_absent() and so on and we still need to take
into account the possible error return value (since we need to deal
with that to avoid accessing hardware upon resume). So instead I added
kernel-doc to both functions mentioning that the card may not be
present after the function has returned.
drivers/pci/hotplug/pciehp.h | 6 ++--
drivers/pci/hotplug/pciehp_core.c | 11 ++++--
drivers/pci/hotplug/pciehp_ctrl.c | 4 +--
drivers/pci/hotplug/pciehp_hpc.c | 59 +++++++++++++++++++++++++------
4 files changed, 61 insertions(+), 19 deletions(-)
diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
index 654c972b8ea0..afea59a3aad2 100644
--- a/drivers/pci/hotplug/pciehp.h
+++ b/drivers/pci/hotplug/pciehp.h
@@ -172,10 +172,10 @@ void pciehp_set_indicators(struct controller *ctrl, int pwr, int attn);
void pciehp_get_latch_status(struct controller *ctrl, u8 *status);
int pciehp_query_power_fault(struct controller *ctrl);
-bool pciehp_card_present(struct controller *ctrl);
-bool pciehp_card_present_or_link_active(struct controller *ctrl);
+int pciehp_card_present(struct controller *ctrl);
+int pciehp_card_present_or_link_active(struct controller *ctrl);
int pciehp_check_link_status(struct controller *ctrl);
-bool pciehp_check_link_active(struct controller *ctrl);
+int pciehp_check_link_active(struct controller *ctrl);
void pciehp_release_ctrl(struct controller *ctrl);
int pciehp_sysfs_enable_slot(struct hotplug_slot *hotplug_slot);
diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
index 56daad828c9e..312cc45c44c7 100644
--- a/drivers/pci/hotplug/pciehp_core.c
+++ b/drivers/pci/hotplug/pciehp_core.c
@@ -139,10 +139,15 @@ static int get_adapter_status(struct hotplug_slot *hotplug_slot, u8 *value)
{
struct controller *ctrl = to_ctrl(hotplug_slot);
struct pci_dev *pdev = ctrl->pcie->port;
+ int ret;
pci_config_pm_runtime_get(pdev);
- *value = pciehp_card_present_or_link_active(ctrl);
+ ret = pciehp_card_present_or_link_active(ctrl);
pci_config_pm_runtime_put(pdev);
+ if (ret < 0)
+ return ret;
+
+ *value = ret;
return 0;
}
@@ -158,13 +163,13 @@ static int get_adapter_status(struct hotplug_slot *hotplug_slot, u8 *value)
*/
static void pciehp_check_presence(struct controller *ctrl)
{
- bool occupied;
+ int occupied;
down_read(&ctrl->reset_lock);
mutex_lock(&ctrl->state_lock);
occupied = pciehp_card_present_or_link_active(ctrl);
- if ((occupied && (ctrl->state == OFF_STATE ||
+ if ((occupied > 0 && (ctrl->state == OFF_STATE ||
ctrl->state == BLINKINGON_STATE)) ||
(!occupied && (ctrl->state == ON_STATE ||
ctrl->state == BLINKINGOFF_STATE)))
diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
index 21af7b16d7a4..c760a13ec7b1 100644
--- a/drivers/pci/hotplug/pciehp_ctrl.c
+++ b/drivers/pci/hotplug/pciehp_ctrl.c
@@ -226,7 +226,7 @@ void pciehp_handle_disable_request(struct controller *ctrl)
void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
{
- bool present, link_active;
+ int present, link_active;
/*
* If the slot is on and presence or link has changed, turn it off.
@@ -257,7 +257,7 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
mutex_lock(&ctrl->state_lock);
present = pciehp_card_present(ctrl);
link_active = pciehp_check_link_active(ctrl);
- if (!present && !link_active) {
+ if (present <= 0 && link_active <= 0) {
mutex_unlock(&ctrl->state_lock);
return;
}
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 1a522c1c4177..526a8f70bac5 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -201,17 +201,29 @@ static void pcie_write_cmd_nowait(struct controller *ctrl, u16 cmd, u16 mask)
pcie_do_write_cmd(ctrl, cmd, mask, false);
}
-bool pciehp_check_link_active(struct controller *ctrl)
+/**
+ * pciehp_check_link_active() - Is the link active
+ * @ctrl: PCIe hotplug controller
+ *
+ * Check whether the downstream link is currently active. Note it is
+ * possible that the card is removed immediately after this so the
+ * caller may need to take it into account.
+ *
+ * If the hotplug controller itself is not available anymore returns
+ * %-ENODEV.
+ */
+int pciehp_check_link_active(struct controller *ctrl)
{
struct pci_dev *pdev = ctrl_dev(ctrl);
u16 lnk_status;
- bool ret;
+ int ret;
- pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
- ret = !!(lnk_status & PCI_EXP_LNKSTA_DLLLA);
+ ret = pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
+ if (ret == PCIBIOS_DEVICE_NOT_FOUND || lnk_status == (u16)~0)
+ return -ENODEV;
- if (ret)
- ctrl_dbg(ctrl, "%s: lnk_status = %x\n", __func__, lnk_status);
+ ret = !!(lnk_status & PCI_EXP_LNKSTA_DLLLA);
+ ctrl_dbg(ctrl, "%s: lnk_status = %x\n", __func__, lnk_status);
return ret;
}
@@ -373,13 +385,29 @@ void pciehp_get_latch_status(struct controller *ctrl, u8 *status)
*status = !!(slot_status & PCI_EXP_SLTSTA_MRLSS);
}
-bool pciehp_card_present(struct controller *ctrl)
+/**
+ * pciehp_card_present() - Is the card present
+ * @ctrl: PCIe hotplug controller
+ *
+ * Function checks whether the card is currently present in the slot and
+ * in that case returns true. Note it is possible that the card is
+ * removed immediately after the check so the caller may need to take
+ * this into account.
+ *
+ * It the hotplug controller itself is not available anymore returns
+ * %-ENODEV.
+ */
+int pciehp_card_present(struct controller *ctrl)
{
struct pci_dev *pdev = ctrl_dev(ctrl);
u16 slot_status;
+ int ret;
- pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
- return slot_status & PCI_EXP_SLTSTA_PDS;
+ ret = pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
+ if (ret == PCIBIOS_DEVICE_NOT_FOUND || slot_status == (u16)~0)
+ return -ENODEV;
+
+ return !!(slot_status & PCI_EXP_SLTSTA_PDS);
}
/**
@@ -390,10 +418,19 @@ bool pciehp_card_present(struct controller *ctrl)
* Presence Detect State bit, this helper also returns true if the Link Active
* bit is set. This is a concession to broken hotplug ports which hardwire
* Presence Detect State to zero, such as Wilocity's [1ae9:0200].
+ *
+ * Returns: %1 if the slot is occupied and %0 if it is not. If the hotplug
+ * port is not present anymore returns %-ENODEV.
*/
-bool pciehp_card_present_or_link_active(struct controller *ctrl)
+int pciehp_card_present_or_link_active(struct controller *ctrl)
{
- return pciehp_card_present(ctrl) || pciehp_check_link_active(ctrl);
+ int ret;
+
+ ret = pciehp_card_present(ctrl);
+ if (ret)
+ return ret;
+
+ return pciehp_check_link_active(ctrl);
}
int pciehp_query_power_fault(struct controller *ctrl)
--
2.23.0
On Tue, Oct 29, 2019 at 08:00:22PM +0300, Mika Westerberg wrote:
> If there are more than one PCIe switch with hotplug downstream ports
> hot-removing them leads to a following deadlock:
Does this happen if two sibling switches are removed simultaneously,
or does this happen when switch A leads to switch B and you remove
switch A (with obviously also removes switch B)? I'm guessing the
latter because it would be easier to reproduce. And I guess that's
obvious from the text below.
> INFO: task irq/126-pciehp:198 blocked for more than 120 seconds.
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> irq/126-pciehp D 0 198 2 0x80000000
> Call Trace:
> __schedule+0x2a2/0x880
> schedule+0x2c/0x80
> schedule_timeout+0x246/0x350
> ? ttwu_do_activate+0x67/0x90
> wait_for_completion+0xb7/0x140
> ? wake_up_q+0x80/0x80
> kthread_stop+0x49/0x110
> __free_irq+0x15c/0x2a0
> free_irq+0x32/0x70
> pcie_shutdown_notification+0x2f/0x50
> pciehp_remove+0x27/0x50
> pcie_port_remove_service+0x36/0x50
> device_release_driver_internal+0x18c/0x250
> device_release_driver+0x12/0x20
> bus_remove_device+0xec/0x160
> device_del+0x13b/0x350
> ? pcie_port_find_device+0x60/0x60
> device_unregister+0x1a/0x60
> remove_iter+0x1e/0x30
> device_for_each_child+0x56/0x90
> pcie_port_device_remove+0x22/0x40
> pcie_portdrv_remove+0x20/0x60
> pci_device_remove+0x3e/0xc0
> device_release_driver_internal+0x18c/0x250
> device_release_driver+0x12/0x20
> pci_stop_bus_device+0x6f/0x90
> pci_stop_bus_device+0x31/0x90
> pci_stop_and_remove_bus_device+0x12/0x20
> pciehp_unconfigure_device+0x88/0x140
> pciehp_disable_slot+0x6a/0x110
> pciehp_handle_presence_or_link_change+0x263/0x400
> pciehp_ist+0x1c9/0x1d0
> ? irq_forced_thread_fn+0x80/0x80
> irq_thread_fn+0x24/0x60
> irq_thread+0xeb/0x190
> ? irq_thread_fn+0x60/0x60
> kthread+0x120/0x140
> ? irq_thread_check_affinity+0xf0/0xf0
> ? kthread_park+0x90/0x90
> ret_from_fork+0x35/0x40
> INFO: task irq/190-pciehp:2288 blocked for more than 120 seconds.
> irq/190-pciehp D 0 2288 2 0x80000000
> Call Trace:
> __schedule+0x2a2/0x880
> schedule+0x2c/0x80
> schedule_preempt_disabled+0xe/0x10
> __mutex_lock.isra.9+0x2e0/0x4d0
> ? __mutex_lock_slowpath+0x13/0x20
> __mutex_lock_slowpath+0x13/0x20
> mutex_lock+0x2c/0x30
> pci_lock_rescan_remove+0x15/0x20
> pciehp_unconfigure_device+0x4d/0x140
> pciehp_disable_slot+0x6a/0x110
> pciehp_handle_presence_or_link_change+0x263/0x400
> pciehp_ist+0x1c9/0x1d0
> ? irq_forced_thread_fn+0x80/0x80
> irq_thread_fn+0x24/0x60
> irq_thread+0xeb/0x190
> ? irq_thread_fn+0x60/0x60
> kthread+0x120/0x140
> ? irq_thread_check_affinity+0xf0/0xf0
> ? kthread_park+0x90/0x90
> ret_from_fork+0x35/0x40
>
> What happens here is that the whole hierarchy is runtime resumed and the
What is the runtime resume connection here? I do see that
pcie_portdrv_remove() may call pm_runtime_forbid(), which looks like
it resumes devices, but I don't see whether that's actually relevant
to the deadlock.
> parent PCIe downstream port, who got the hot-remove event, starts
> removing devices below it taking pci_lock_rescan_remove() lock. When the
> child PCIe port is runtime resumed it calls pciehp_check_presence()
> which ends up calling pciehp_card_present() and pciehp_check_link_active().
Oh, I see, pciehp_resume() calls pciehp_check_presence(), which
schedules the IRQ thread via pciehp_request(). So does this deadlock
only happen if the port(s) have been runtime suspended?
> Both of these read their parts of PCIe config space by calling helper
> function pcie_capability_read_word(). Now, this function notices that
> the underlying device is already gone and returns PCIBIOS_DEVICE_NOT_FOUND
> with the capability value set to 0. When pciehp gets this value it
> thinks that its child device is also hot-removed and schedules its IRQ
> thread to handle the event.
The child device actually *has* been hot-removed, right? :)
In addition to checking for PCIBIOS_DEVICE_NOT_FOUND, you added checks
for ~0:
> + ret = pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
> + if (ret == PCIBIOS_DEVICE_NOT_FOUND || lnk_status == (u16)~0)
> + return -ENODEV;
That makes sense to me and I think it's the right thing to do.
But I do wonder whether pcie_capability_read_word() is doing the wrong
thing when it sets "*val = 0" in the error case. I suspect that just
complicates the callers for no good reason. The callers could
otherwise simply check for ~0 as a "this may be an error response"
value.
> The deadlock happens when the child's IRQ thread runs and tries to
> acquire pci_lock_rescan_remove() which is already taken by the parent
> and the parent waits for the child's IRQ thread to finish.
>
> We can prevent this from happening by checking the return value of
> pcie_capability_read_word() and if it is PCIBIOS_DEVICE_NOT_FOUND stop
> performing any hot-removal activities.
>
> Signed-off-by: Mika Westerberg <[email protected]>
> Tested-by: Kai-Heng Feng <[email protected]>
> ---
> Changes from v2 (https://patchwork.kernel.org/patch/11089973/):
>
> * Check for ~0 as well
> * Added tag from Kai-Heng
> * Always log lnk_status in pciehp_check_link_active()
> * I also experimented renaming the two functions to pciehp_card_absent()
> and pciehp_check_link_down() but it ended up looking odd because now we
> check for !pciehp_card_absent() and so on and we still need to take
> into account the possible error return value (since we need to deal
> with that to avoid accessing hardware upon resume). So instead I added
> kernel-doc to both functions mentioning that the card may not be
> present after the function has returned.
>
> drivers/pci/hotplug/pciehp.h | 6 ++--
> drivers/pci/hotplug/pciehp_core.c | 11 ++++--
> drivers/pci/hotplug/pciehp_ctrl.c | 4 +--
> drivers/pci/hotplug/pciehp_hpc.c | 59 +++++++++++++++++++++++++------
> 4 files changed, 61 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
> index 654c972b8ea0..afea59a3aad2 100644
> --- a/drivers/pci/hotplug/pciehp.h
> +++ b/drivers/pci/hotplug/pciehp.h
> @@ -172,10 +172,10 @@ void pciehp_set_indicators(struct controller *ctrl, int pwr, int attn);
>
> void pciehp_get_latch_status(struct controller *ctrl, u8 *status);
> int pciehp_query_power_fault(struct controller *ctrl);
> -bool pciehp_card_present(struct controller *ctrl);
> -bool pciehp_card_present_or_link_active(struct controller *ctrl);
> +int pciehp_card_present(struct controller *ctrl);
> +int pciehp_card_present_or_link_active(struct controller *ctrl);
> int pciehp_check_link_status(struct controller *ctrl);
> -bool pciehp_check_link_active(struct controller *ctrl);
> +int pciehp_check_link_active(struct controller *ctrl);
> void pciehp_release_ctrl(struct controller *ctrl);
>
> int pciehp_sysfs_enable_slot(struct hotplug_slot *hotplug_slot);
> diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
> index 56daad828c9e..312cc45c44c7 100644
> --- a/drivers/pci/hotplug/pciehp_core.c
> +++ b/drivers/pci/hotplug/pciehp_core.c
> @@ -139,10 +139,15 @@ static int get_adapter_status(struct hotplug_slot *hotplug_slot, u8 *value)
> {
> struct controller *ctrl = to_ctrl(hotplug_slot);
> struct pci_dev *pdev = ctrl->pcie->port;
> + int ret;
>
> pci_config_pm_runtime_get(pdev);
> - *value = pciehp_card_present_or_link_active(ctrl);
> + ret = pciehp_card_present_or_link_active(ctrl);
> pci_config_pm_runtime_put(pdev);
> + if (ret < 0)
> + return ret;
> +
> + *value = ret;
> return 0;
> }
>
> @@ -158,13 +163,13 @@ static int get_adapter_status(struct hotplug_slot *hotplug_slot, u8 *value)
> */
> static void pciehp_check_presence(struct controller *ctrl)
> {
> - bool occupied;
> + int occupied;
>
> down_read(&ctrl->reset_lock);
> mutex_lock(&ctrl->state_lock);
>
> occupied = pciehp_card_present_or_link_active(ctrl);
> - if ((occupied && (ctrl->state == OFF_STATE ||
> + if ((occupied > 0 && (ctrl->state == OFF_STATE ||
> ctrl->state == BLINKINGON_STATE)) ||
> (!occupied && (ctrl->state == ON_STATE ||
> ctrl->state == BLINKINGOFF_STATE)))
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index 21af7b16d7a4..c760a13ec7b1 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -226,7 +226,7 @@ void pciehp_handle_disable_request(struct controller *ctrl)
>
> void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
> {
> - bool present, link_active;
> + int present, link_active;
>
> /*
> * If the slot is on and presence or link has changed, turn it off.
> @@ -257,7 +257,7 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
> mutex_lock(&ctrl->state_lock);
> present = pciehp_card_present(ctrl);
> link_active = pciehp_check_link_active(ctrl);
> - if (!present && !link_active) {
> + if (present <= 0 && link_active <= 0) {
> mutex_unlock(&ctrl->state_lock);
> return;
> }
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 1a522c1c4177..526a8f70bac5 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -201,17 +201,29 @@ static void pcie_write_cmd_nowait(struct controller *ctrl, u16 cmd, u16 mask)
> pcie_do_write_cmd(ctrl, cmd, mask, false);
> }
>
> -bool pciehp_check_link_active(struct controller *ctrl)
> +/**
> + * pciehp_check_link_active() - Is the link active
> + * @ctrl: PCIe hotplug controller
> + *
> + * Check whether the downstream link is currently active. Note it is
> + * possible that the card is removed immediately after this so the
> + * caller may need to take it into account.
> + *
> + * If the hotplug controller itself is not available anymore returns
> + * %-ENODEV.
> + */
> +int pciehp_check_link_active(struct controller *ctrl)
> {
> struct pci_dev *pdev = ctrl_dev(ctrl);
> u16 lnk_status;
> - bool ret;
> + int ret;
>
> - pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
> - ret = !!(lnk_status & PCI_EXP_LNKSTA_DLLLA);
> + ret = pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
> + if (ret == PCIBIOS_DEVICE_NOT_FOUND || lnk_status == (u16)~0)
> + return -ENODEV;
>
> - if (ret)
> - ctrl_dbg(ctrl, "%s: lnk_status = %x\n", __func__, lnk_status);
> + ret = !!(lnk_status & PCI_EXP_LNKSTA_DLLLA);
> + ctrl_dbg(ctrl, "%s: lnk_status = %x\n", __func__, lnk_status);
>
> return ret;
> }
> @@ -373,13 +385,29 @@ void pciehp_get_latch_status(struct controller *ctrl, u8 *status)
> *status = !!(slot_status & PCI_EXP_SLTSTA_MRLSS);
> }
>
> -bool pciehp_card_present(struct controller *ctrl)
> +/**
> + * pciehp_card_present() - Is the card present
> + * @ctrl: PCIe hotplug controller
> + *
> + * Function checks whether the card is currently present in the slot and
> + * in that case returns true. Note it is possible that the card is
> + * removed immediately after the check so the caller may need to take
> + * this into account.
> + *
> + * It the hotplug controller itself is not available anymore returns
> + * %-ENODEV.
> + */
> +int pciehp_card_present(struct controller *ctrl)
> {
> struct pci_dev *pdev = ctrl_dev(ctrl);
> u16 slot_status;
> + int ret;
>
> - pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
> - return slot_status & PCI_EXP_SLTSTA_PDS;
> + ret = pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
> + if (ret == PCIBIOS_DEVICE_NOT_FOUND || slot_status == (u16)~0)
> + return -ENODEV;
> +
> + return !!(slot_status & PCI_EXP_SLTSTA_PDS);
> }
>
> /**
> @@ -390,10 +418,19 @@ bool pciehp_card_present(struct controller *ctrl)
> * Presence Detect State bit, this helper also returns true if the Link Active
> * bit is set. This is a concession to broken hotplug ports which hardwire
> * Presence Detect State to zero, such as Wilocity's [1ae9:0200].
> + *
> + * Returns: %1 if the slot is occupied and %0 if it is not. If the hotplug
> + * port is not present anymore returns %-ENODEV.
> */
> -bool pciehp_card_present_or_link_active(struct controller *ctrl)
> +int pciehp_card_present_or_link_active(struct controller *ctrl)
> {
> - return pciehp_card_present(ctrl) || pciehp_check_link_active(ctrl);
> + int ret;
> +
> + ret = pciehp_card_present(ctrl);
> + if (ret)
> + return ret;
> +
> + return pciehp_check_link_active(ctrl);
> }
>
> int pciehp_query_power_fault(struct controller *ctrl)
> --
> 2.23.0
>
On Tue, Nov 12, 2019 at 09:17:52PM -0600, Bjorn Helgaas wrote:
> On Tue, Oct 29, 2019 at 08:00:22PM +0300, Mika Westerberg wrote:
> > parent PCIe downstream port, who got the hot-remove event, starts
> > removing devices below it taking pci_lock_rescan_remove() lock. When the
> > child PCIe port is runtime resumed it calls pciehp_check_presence()
> > which ends up calling pciehp_card_present() and pciehp_check_link_active().
>
> Oh, I see, pciehp_resume() calls pciehp_check_presence(), which
> schedules the IRQ thread via pciehp_request(). So does this deadlock
> only happen if the port(s) have been runtime suspended?
No, there is a multitude of situations when the deadlock may occur and
this is just one of them. See my comment on v1 of this patch:
https://patchwork.ozlabs.org/patch/1117870/#2230798
Thanks,
Lukas
On Tue, Nov 12, 2019 at 09:17:52PM -0600, Bjorn Helgaas wrote:
> On Tue, Oct 29, 2019 at 08:00:22PM +0300, Mika Westerberg wrote:
> > If there are more than one PCIe switch with hotplug downstream ports
> > hot-removing them leads to a following deadlock:
>
> Does this happen if two sibling switches are removed simultaneously,
> or does this happen when switch A leads to switch B and you remove
> switch A (with obviously also removes switch B)? I'm guessing the
> latter because it would be easier to reproduce. And I guess that's
> obvious from the text below.
Yes, that's right.
> > INFO: task irq/126-pciehp:198 blocked for more than 120 seconds.
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > irq/126-pciehp D 0 198 2 0x80000000
> > Call Trace:
> > __schedule+0x2a2/0x880
> > schedule+0x2c/0x80
> > schedule_timeout+0x246/0x350
> > ? ttwu_do_activate+0x67/0x90
> > wait_for_completion+0xb7/0x140
> > ? wake_up_q+0x80/0x80
> > kthread_stop+0x49/0x110
> > __free_irq+0x15c/0x2a0
> > free_irq+0x32/0x70
> > pcie_shutdown_notification+0x2f/0x50
> > pciehp_remove+0x27/0x50
> > pcie_port_remove_service+0x36/0x50
> > device_release_driver_internal+0x18c/0x250
> > device_release_driver+0x12/0x20
> > bus_remove_device+0xec/0x160
> > device_del+0x13b/0x350
> > ? pcie_port_find_device+0x60/0x60
> > device_unregister+0x1a/0x60
> > remove_iter+0x1e/0x30
> > device_for_each_child+0x56/0x90
> > pcie_port_device_remove+0x22/0x40
> > pcie_portdrv_remove+0x20/0x60
> > pci_device_remove+0x3e/0xc0
> > device_release_driver_internal+0x18c/0x250
> > device_release_driver+0x12/0x20
> > pci_stop_bus_device+0x6f/0x90
> > pci_stop_bus_device+0x31/0x90
> > pci_stop_and_remove_bus_device+0x12/0x20
> > pciehp_unconfigure_device+0x88/0x140
> > pciehp_disable_slot+0x6a/0x110
> > pciehp_handle_presence_or_link_change+0x263/0x400
> > pciehp_ist+0x1c9/0x1d0
> > ? irq_forced_thread_fn+0x80/0x80
> > irq_thread_fn+0x24/0x60
> > irq_thread+0xeb/0x190
> > ? irq_thread_fn+0x60/0x60
> > kthread+0x120/0x140
> > ? irq_thread_check_affinity+0xf0/0xf0
> > ? kthread_park+0x90/0x90
> > ret_from_fork+0x35/0x40
> > INFO: task irq/190-pciehp:2288 blocked for more than 120 seconds.
> > irq/190-pciehp D 0 2288 2 0x80000000
> > Call Trace:
> > __schedule+0x2a2/0x880
> > schedule+0x2c/0x80
> > schedule_preempt_disabled+0xe/0x10
> > __mutex_lock.isra.9+0x2e0/0x4d0
> > ? __mutex_lock_slowpath+0x13/0x20
> > __mutex_lock_slowpath+0x13/0x20
> > mutex_lock+0x2c/0x30
> > pci_lock_rescan_remove+0x15/0x20
> > pciehp_unconfigure_device+0x4d/0x140
> > pciehp_disable_slot+0x6a/0x110
> > pciehp_handle_presence_or_link_change+0x263/0x400
> > pciehp_ist+0x1c9/0x1d0
> > ? irq_forced_thread_fn+0x80/0x80
> > irq_thread_fn+0x24/0x60
> > irq_thread+0xeb/0x190
> > ? irq_thread_fn+0x60/0x60
> > kthread+0x120/0x140
> > ? irq_thread_check_affinity+0xf0/0xf0
> > ? kthread_park+0x90/0x90
> > ret_from_fork+0x35/0x40
> >
> > What happens here is that the whole hierarchy is runtime resumed and the
>
> What is the runtime resume connection here? I do see that
> pcie_portdrv_remove() may call pm_runtime_forbid(), which looks like
> it resumes devices, but I don't see whether that's actually relevant
> to the deadlock.
When the parent port removes its children the driver core
(__device_release_driver) calls pm_runtime_get_sync() for the device
which ends up calling the resume hook of the child pciehp.
> > parent PCIe downstream port, who got the hot-remove event, starts
> > removing devices below it taking pci_lock_rescan_remove() lock. When the
> > child PCIe port is runtime resumed it calls pciehp_check_presence()
> > which ends up calling pciehp_card_present() and pciehp_check_link_active().
>
> Oh, I see, pciehp_resume() calls pciehp_check_presence(), which
> schedules the IRQ thread via pciehp_request(). So does this deadlock
> only happen if the port(s) have been runtime suspended?
I'm aware of two cases where this happens with a real hardware.
First one is that all involved ports are runtime suspended and you
unplug them. This can happen easily if the drivers involved
automatically enable runtime PM (xHCI for example does that).
The other more common case is that you suspend your laptop (close the
lid with the dock + something else connected. Then you unplug the dock
and after some time open the lid. Basically system suspend/resume cycle
so that you unplug the devices when it is suspended.
This patch helps for both cases above.
As Lukas commented there is also a bit more syntetic case where the
removal is done through sysfs in paraller to hot-removing the device. I
believe this one is still unfixed.
> > Both of these read their parts of PCIe config space by calling helper
> > function pcie_capability_read_word(). Now, this function notices that
> > the underlying device is already gone and returns PCIBIOS_DEVICE_NOT_FOUND
> > with the capability value set to 0. When pciehp gets this value it
> > thinks that its child device is also hot-removed and schedules its IRQ
> > thread to handle the event.
>
> The child device actually *has* been hot-removed, right? :)
Yes.
> In addition to checking for PCIBIOS_DEVICE_NOT_FOUND, you added checks
> for ~0:
>
> > + ret = pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
> > + if (ret == PCIBIOS_DEVICE_NOT_FOUND || lnk_status == (u16)~0)
> > + return -ENODEV;
>
> That makes sense to me and I think it's the right thing to do.
So do I :)
> But I do wonder whether pcie_capability_read_word() is doing the wrong
> thing when it sets "*val = 0" in the error case. I suspect that just
> complicates the callers for no good reason. The callers could
> otherwise simply check for ~0 as a "this may be an error response"
> value.
I agree.
We discussed about that in v2 and you said that you would like to
explore removal of "*val = 0" but not in the context of this issue [1].
[1] https://patchwork.kernel.org/patch/11089973/#22961207