Re: [Kernel Bug] INFO: task hung in show_cons_active

[Greg KH]

On Tue, Jun 30, 2026 at 08:30:39PM +0800, Longxing Li wrote:
>  Dear maintainers,
> 
> Here's my fix and patch of the bug.
> 
> Fix Summary:
> 
>   The deadlock occurs because unregister_console() holds console_list_lock
>   while __pr_flush() blocks on console_sem. show_cons_active() has the same
>   lock -> sem ordering (holds mutex, waits for sem), creating a potential
>   ABBA when any printer path needs the mutex.
> 
>   Fix: restructure unregister_console() into three phases:
> 
>     Phase 1 (list lock):   Disable console (clear CON_ENABLED).
>     Phase 2 (NO lock):     __pr_flush() waits for pending output.
>                            Safe because console is already disabled.
>     Phase 3 (list lock):   Remove from list + cleanup.
> 
>   This ensures __pr_flush() is never called while holding console_list_lock,
>   eliminating the lock inversion.
> 
>   Full patch is as follows and also attached in the link.
> 
> =====================================================
> From: Longxing Li <coregee2000@xxxxxxxxx>
> Date: Tue, 30 Jun 2026
> Subject: [PATCH] printk: fix potential deadlock in unregister_console()
> 
> unregister_console() holds console_list_lock while calling __pr_flush(),
> which blocks on console_sem. show_cons_active() holds console_mutex (the
> same lock) while also waiting for console_sem. This creates a potential
> ABBA deadlock when any console output path needs console_mutex.
> 
> Fix by restructuring unregister_console() so __pr_flush() is called WITHOUT
> holding console_list_lock:
> 
>   Phase 1 (list lock):    Disable console (clear CON_ENABLED).
>   Phase 2 (no lock):      __pr_flush() drains pending output.
>   Phase 3 (list lock):    Remove from list + cleanup.
> 
> Reported-by: Longxing Li

You are the author, noneed for a reported-by

> Suggested-by: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>

I did?

> Signed-off-by: Longxing Li <coregee2000@xxxxxxxxx>
> ---
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -4235,28 +4235,15 @@
>   struct console *c;
>   int res;
> 
>   lockdep_assert_console_list_lock_held();
> 
> - con_printk(KERN_INFO, console, "disabled\n");
> -

Patch is corruupted and can not be applied :(