[PATCH v2] pciehp: fix a race between pciehp and removing operations by sysfs

From: Xiongfeng Wang
Date: Mon Aug 05 2019 - 08:35:42 EST

Next message: David Sterba: "Re: [PATCH][btrfs-next] btrfs: fix spelling mistake "aliged" -> "aligned""
Previous message: Etienne Carriere: "Re: [PATCH v2 6/6] firmware: arm_scmi: Check if platform has released shmem before using"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

When I unplug a pcie slot and remove the pcie device by 'sysfs' at the
same time, I got the following calltrace.

INFO: task irq/746-pciehp:41551 blocked for more than 120 seconds.
Tainted: P W OE 4.19.25-vhulk1901.1.0.h111.aarch64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
irq/746-pciehp D 0 41551 2 0x00000228
Call trace:
__switch_to+0x94/0xe8
__schedule+0x270/0x8b0
schedule+0x2c/0x88
schedule_preempt_disabled+0x14/0x20
__mutex_lock.isra.1+0x1fc/0x540
__mutex_lock_slowpath+0x24/0x30
mutex_lock+0x80/0xa8
pci_lock_rescan_remove+0x20/0x28
pciehp_configure_device+0x30/0x140
pciehp_handle_presence_or_link_change+0x35c/0x4b0
pciehp_ist+0x1cc/0x1d0
irq_thread_fn+0x30/0x80
irq_thread+0x128/0x200
kthread+0x134/0x138
ret_from_fork+0x10/0x18
INFO: task bash:6424 blocked for more than 120 seconds.
Tainted: P W OE 4.19.25-vhulk1901.1.0.h111.aarch64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
bash D 0 6424 2231 0x00000200
Call trace:
__switch_to+0x94/0xe8
__schedule+0x270/0x8b0
schedule+0x2c/0x88
schedule_timeout+0x224/0x448
wait_for_common+0x198/0x2a0
wait_for_completion+0x28/0x38
kthread_stop+0x60/0x190
__free_irq+0x1c0/0x348
free_irq+0x40/0x88
pcie_shutdown_notification+0x54/0x80
pciehp_remove+0x30/0x50
pcie_port_remove_service+0x3c/0x58
device_release_driver_internal+0x1b4/0x250
device_release_driver+0x28/0x38
bus_remove_device+0xd4/0x160
device_del+0x128/0x348
device_unregister+0x24/0x78
remove_iter+0x48/0x58
device_for_each_child+0x6c/0xb8
pcie_port_device_remove+0x2c/0x48
pcie_portdrv_remove+0x5c/0x68
pci_device_remove+0x48/0xd8
device_release_driver_internal+0x1b4/0x250
device_release_driver+0x28/0x38
pci_stop_bus_device+0x84/0xb8
pci_stop_and_remove_bus_device_locked+0x24/0x40
remove_store+0xa4/0xb8
dev_attr_store+0x44/0x60
sysfs_kf_write+0x58/0x80
kernfs_fop_write+0xe8/0x1f0
__vfs_write+0x60/0x190
vfs_write+0xac/0x1c0
ksys_write+0x6c/0xd8
__arm64_sys_write+0x24/0x30
el0_svc_common+0xa0/0x180
el0_svc_handler+0x38/0x78
el0_svc+0x8/0xc

When we remove a slot by sysfs.
'pci_stop_and_remove_bus_device_locked()' will be called. This function
will get the global mutex lock 'pci_rescan_remove_lock', and remove the
slot. If the irq thread 'pciehp_ist' is still running, we will wait
until it exits.

If a pciehp interrupt happens immediately after we remove the slot by
sysfs, but before we free the pciehp irq in
'pci_stop_and_remove_bus_device_locked()'. 'pciehp_ist' will hung
because the global mutex lock 'pci_rescan_remove_lock' is held by the
sysfs operation. But the sysfs operation is waiting for the pciehp irq
thread 'pciehp_ist' ends. Then a hung task occurs.

So this two kinds of operation, removing the slot triggered by pciehp
interrupt and removing through 'sysfs', should not be excuted at the
same time. This patch add a global variable to mark that one of these
operations is under processing. When this variable is set, if another
operation is requested, it will be rejected.

Signed-off-by: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
---
drivers/pci/hotplug/pciehp.h | 3 +++
drivers/pci/hotplug/pciehp_ctrl.c | 13 ++++++++++
drivers/pci/hotplug/pciehp_hpc.c | 52 +++++++++++++++++++++++++++++++++++----
drivers/pci/pci-sysfs.c | 7 ++++++
drivers/pci/remove.c | 5 ++++
include/linux/pci.h | 3 +++
6 files changed, 78 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
index 8c51a04..b8983c1 100644
--- a/drivers/pci/hotplug/pciehp.h
+++ b/drivers/pci/hotplug/pciehp.h
@@ -58,6 +58,8 @@
* used for synchronous writes to the Slot Control register
* @pending_events: used by the IRQ handler to save events retrieved from the
* Slot Status register for later consumption by the IRQ thread
+ * @delayed_events: when we delay an event handling because the slot is being
+ * removed or rescanned, we use this member to pass the delayed event
* @notification_enabled: whether the IRQ was requested successfully
* @power_fault_detected: whether a power fault was detected by the hardware
* that has not yet been cleared by the user
@@ -91,6 +93,7 @@ struct controller {
wait_queue_head_t queue;

atomic_t pending_events; /* event handling */
+ int delayed_events;
unsigned int notification_enabled:1;
unsigned int power_fault_detected;
struct task_struct *poll_thread;
diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
index 631ced0..f8b1212 100644
--- a/drivers/pci/hotplug/pciehp_ctrl.c
+++ b/drivers/pci/hotplug/pciehp_ctrl.c
@@ -141,6 +141,7 @@ void pciehp_queue_pushbutton_work(struct work_struct *work)
{
struct controller *ctrl = container_of(work, struct controller,
button_work.work);
+ int events = ctrl->delayed_events;

mutex_lock(&ctrl->state_lock);
switch (ctrl->state) {
@@ -151,6 +152,12 @@ void pciehp_queue_pushbutton_work(struct work_struct *work)
pciehp_request(ctrl, PCI_EXP_SLTSTA_PDC);
break;
default:
+ if (events) {
+ atomic_or(events, &ctrl->pending_events);
+ if (!pciehp_poll_mode)
+ irq_wake_thread(ctrl->pcie->irq, ctrl);
+ } else
+ slot_being_removed_rescanned = 0;
break;
}
mutex_unlock(&ctrl->state_lock);
@@ -174,6 +181,7 @@ void pciehp_handle_button_press(struct controller *ctrl)
/* blink green LED and turn off amber */
pciehp_green_led_blink(ctrl);
pciehp_set_attention_status(ctrl, 0);
+ ctrl->delayed_events = 0;
schedule_delayed_work(&ctrl->button_work, 5 * HZ);
break;
case BLINKINGOFF_STATE:
@@ -195,10 +203,12 @@ void pciehp_handle_button_press(struct controller *ctrl)
pciehp_set_attention_status(ctrl, 0);
ctrl_info(ctrl, "Slot(%s): Action canceled due to button press\n",
slot_name(ctrl));
+ slot_being_removed_rescanned = 0;
break;
default:
ctrl_err(ctrl, "Slot(%s): Ignoring invalid state %#x\n",
slot_name(ctrl), ctrl->state);
+ slot_being_removed_rescanned = 0;
break;
}
mutex_unlock(&ctrl->state_lock);
@@ -217,6 +227,7 @@ void pciehp_handle_disable_request(struct controller *ctrl)
mutex_unlock(&ctrl->state_lock);

ctrl->request_result = pciehp_disable_slot(ctrl, SAFE_REMOVAL);
+ slot_being_removed_rescanned = 0;
}

void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
@@ -254,6 +265,7 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
link_active = pciehp_check_link_active(ctrl);
if (!present && !link_active) {
mutex_unlock(&ctrl->state_lock);
+ slot_being_removed_rescanned = 0;
return;
}

@@ -276,6 +288,7 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
mutex_unlock(&ctrl->state_lock);
break;
}
+ slot_being_removed_rescanned = 0;
}

static int __pciehp_enable_slot(struct controller *ctrl)
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index bd990e3..2db4731 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -631,7 +631,16 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
if (events & PCI_EXP_SLTSTA_ABP) {
ctrl_info(ctrl, "Slot(%s): Attention button pressed\n",
slot_name(ctrl));
- pciehp_handle_button_press(ctrl);
+ if (!test_and_set_bit(0, &slot_being_removed_rescanned))
+ pciehp_handle_button_press(ctrl);
+ else {
+ if (ctrl->state == BLINKINGOFF_STATE ||
+ ctrl->state == BLINKINGON_STATE)
+ pciehp_handle_button_press(ctrl);
+ else
+ ctrl_info(ctrl, "Slot(%s): Slot operation failed because a remove or rescan operation is under processing, please try later!\n",
+ slot_name(ctrl));
+ }
}

/* Check Power Fault Detected */
@@ -647,10 +656,43 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
* or Data Link Layer State Changed events.
*/
down_read(&ctrl->reset_lock);
- if (events & DISABLE_SLOT)
- pciehp_handle_disable_request(ctrl);
- else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC))
- pciehp_handle_presence_or_link_change(ctrl, events);
+ if (events & DISABLE_SLOT) {
+ if (!test_and_set_bit(0, &slot_being_removed_rescanned))
+ pciehp_handle_disable_request(ctrl);
+ else {
+ if (ctrl->state == BLINKINGOFF_STATE ||
+ ctrl->state == BLINKINGON_STATE)
+ pciehp_handle_disable_request(ctrl);
+ /*
+ * If 'button_work.timer' is pending, delay the work
+ * will cause BUG_ON() in add_timer().
+ */
+ else if (!timer_pending(&ctrl->button_work.timer)) {
+
+ ctrl->delayed_events = DISABLE_SLOT;
+ schedule_delayed_work(&ctrl->button_work,
+ 3 * HZ);
+ }
+ }
+ } else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC)) {
+ if (!test_and_set_bit(0, &slot_being_removed_rescanned))
+ pciehp_handle_presence_or_link_change(ctrl, events);
+ else {
+ if (ctrl->state == BLINKINGOFF_STATE ||
+ ctrl->state == BLINKINGON_STATE)
+ pciehp_handle_presence_or_link_change(ctrl,
+ events);
+ else if (!timer_pending(&ctrl->button_work.timer)) {
+ ctrl_info(ctrl, "Slot(%s): Surprise link down/up in remove or rescan process!\n",
+ slot_name(ctrl));
+ ctrl->delayed_events = events &
+ (PCI_EXP_SLTSTA_PDC |
+ PCI_EXP_SLTSTA_DLLSC);
+ schedule_delayed_work(&ctrl->button_work,
+ 3 * HZ);
+ }
+ }
+ }
up_read(&ctrl->reset_lock);

pci_config_pm_runtime_put(pdev);
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 965c721..8ddfd0d 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -473,11 +473,18 @@ static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
{
unsigned long val;

+ if (test_and_set_bit(0, &slot_being_removed_rescanned)) {
+ pr_info("Slot is being removed or rescanned, please try later!\n");
+ return -EINVAL;
+ }
+
if (kstrtoul(buf, 0, &val) < 0)
return -EINVAL;

if (val && device_remove_file_self(dev, attr))
pci_stop_and_remove_bus_device_locked(to_pci_dev(dev));
+
+ slot_being_removed_rescanned = 0;
return count;
}
static struct device_attribute dev_remove_attr = __ATTR_IGNORE_LOCKDEP(remove,
diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
index e9c6b12..6d15ad0 100644
--- a/drivers/pci/remove.c
+++ b/drivers/pci/remove.c
@@ -3,6 +3,11 @@
#include <linux/module.h>
#include "pci.h"

+/*
+ * When a slot is being removed/rescanned, this flag is set.
+ */
+unsigned long slot_being_removed_rescanned;
+
static void pci_free_resources(struct pci_dev *dev)
{
int i;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 9e700d9..92575ee 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -952,6 +952,9 @@ enum pcie_bus_config_types {
/* Do NOT directly access these two variables, unless you are arch-specific PCI
* code, or PCI core code. */
extern struct list_head pci_root_buses; /* List of all known PCI buses */
+
+extern unsigned long slot_being_removed_rescanned;
+
/* Some device drivers need know if PCI is initiated */
int no_pci_devices(void);

--
1.7.12.4

Next message: David Sterba: "Re: [PATCH][btrfs-next] btrfs: fix spelling mistake "aliged" -> "aligned""
Previous message: Etienne Carriere: "Re: [PATCH v2 6/6] firmware: arm_scmi: Check if platform has released shmem before using"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]