| Message ID | 20240410020615.2885000-1-liu.yec@h3c.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [V10] kdb: Fix the deadlock issue in KDB debugging. | expand |
On Wed, Apr 10, 2024 at 10:06:15AM +0800, liu.yec@h3c.com wrote: > From: LiuYe <liu.yeC@h3c.com> > > Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will > attempt to use schedule_work() to provoke a keyboard reset when > transitioning out of the debugger and back to normal operation. > This can cause deadlock because schedule_work() is not NMI-safe. > > The stack trace below shows an example of the problem. In this > case the master cpu is not running from NMI but it has parked > the slave CPUs using an NMI and the parked CPUs is holding > spinlocks needed by schedule_work(). > > Example: > BUG: spinlock lockup suspected on CPU#0. owner_cpu: 1 > CPU1: Call Trace: > __schedule > schedule > schedule_hrtimeout_range_clock > mutex_unlock > ep_scan_ready_list > schedule_hrtimeout_range > ep_poll > wake_up_q > SyS_epoll_wait > entry_SYSCALL_64_fastpath > > CPU0: Call Trace: > dump_stack > spin_dump > do_raw_spin_lock > _raw_spin_lock > try_to_wake_up > wake_up_process > insert_work > __queue_work > queue_work_on > kgdboc_post_exp_handler > kgdb_cpu_enter > kgdb_handle_exception > __kgdb_notify > kgdb_notify > notifier_call_chain > notify_die > do_int3 > int3 > > We fix the problem by using irq_work to call schedule_work() > instead of calling it directly. This is because we cannot > resynchronize the keyboard state from the hardirq context > provided by irq_work. This must be done from the task context > in order to call the input subsystem. > > Therefore, we have to defer the work twice. First, safely > switch from the debug trap context (similar to NMI) to the > hardirq, and then switch from the hardirq to the system work queue. > > Signed-off-by: LiuYe <liu.yeC@h3c.com> > Co-developed-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Greg KH <gregkh@linuxfoundation.org> I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. greg k-h
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index 7ce7bb164..32410fec7 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -19,6 +19,7 @@ #include <linux/console.h> #include <linux/vt_kern.h> #include <linux/input.h> +#include <linux/irq_work.h> #include <linux/module.h> #include <linux/platform_device.h> #include <linux/serial_core.h> @@ -82,6 +83,19 @@ static struct input_handler kgdboc_reset_handler = { static DEFINE_MUTEX(kgdboc_reset_mutex); +/* + * This code ensures that the keyboard state, which is changed during kdb + * execution, is resynchronized when we leave the debug trap. The resync + * logic calls into the input subsystem to force a reset. The calls into + * the input subsystem must be executed from normal task context. + * + * We need to trigger the resync from the debug trap, which executes in an + * NMI (or similar) context. To make it safe to call into the input + * subsystem we end up having use two deferred execution techniques. + * Firstly, we use irq_work, which is NMI-safe, to provoke a callback from + * hardirq context. Then, from the hardirq callback we use the system + * workqueue to provoke the callback that actually performs the resync. + */ static void kgdboc_restore_input_helper(struct work_struct *dummy) { /* @@ -99,10 +113,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy) static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper); +static void kgdboc_queue_restore_input_helper(struct irq_work *unused) +{ + schedule_work(&kgdboc_restore_input_work); +} + +static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper); + static void kgdboc_restore_input(void) { if (likely(system_state == SYSTEM_RUNNING)) - schedule_work(&kgdboc_restore_input_work); + irq_work_queue(&kgdboc_restore_input_irq_work); } static int kgdboc_register_kbd(char **cptr) @@ -133,6 +154,7 @@ static void kgdboc_unregister_kbd(void) i--; } } + irq_work_sync(&kgdboc_restore_input_irq_work); flush_work(&kgdboc_restore_input_work); } #else /* ! CONFIG_KDB_KEYBOARD */