Re: [PATCH V3] kdb: Fix the deadlock issue in KDB debugging.

Greg KH
2024-03-21T07:38:04Z

On Thu, Mar 21, 2024 at 10:26:04AM +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, namex/10450
> lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1
> ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000
> ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20
> Call Trace:
> [<ffffffff81479e6d>] ? __schedule+0x16d/0xac0
> [<ffffffff8147a7fc>] ? schedule+0x3c/0x90
> [<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120
> [<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10
> [<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0
> [<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20
> [<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0
> [<ffffffff8108c540>] ? wake_up_q+0x70/0x70
> [<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0
> [<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75
> CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1
> Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019
> 0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000
> ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980
> 000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0
> Call Trace:
> <#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2
> [<ffffffff810a7f7f>] spin_dump+0x7f/0x100
> [<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150
> [<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20
> [<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0
> [<ffffffff8108c4c5>] wake_up_process+0x15/0x20
> [<ffffffff8107b371>] insert_work+0x81/0xc0
> [<ffffffff8107b4e5>] __queue_work+0x135/0x390
> [<ffffffff8107b786>] queue_work_on+0x46/0x90
> [<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70
> [<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610
> [<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0
> [<ffffffff81054e21>] __kgdb_notify+0x71/0xd0
> [<ffffffff81054eb5>] kgdb_notify+0x35/0x70
> [<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70
> [<ffffffff8108304d>] notify_die+0x3d/0x50
> [<ffffffff81017219>] do_int3+0x89/0x120
> [<ffffffff81480fb4>] int3+0x44/0x80
>
> Signed-off-by: LiuYe <liu.yeC@h3c.com>
> Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org>
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> ---
> drivers/tty/serial/kgdboc.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index 7ce7bb164..161b25ecc 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -22,6 +22,7 @@
> #include <linux/module.h>
> #include <linux/platform_device.h>
> #include <linux/serial_core.h>
> +#include <linux/irq_work.h>
>
> #define MAX_CONFIG_LEN 40
>
> @@ -99,10 +100,17 @@ 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 +141,7 @@ 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 */
> --
> 2.25.1
>
>

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him
a patch that has triggered this response. He used to manually respond
to these common problems, but in order to save his sanity (he kept
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created. Hopefully you will not take offence and will fix the problem
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Please read the section entitled "The canonical patch format" in the
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