Re: [PATCH v3] mm: Fix possible deadlock in console_trylock_spinning

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 13 Aug 2025 16:53:10 +0800 Gu Bowen <gubowen5@huawei.com> wrote:

> Our syztester report the lockdep WARNING [1]. kmemleak_scan_thread()
> invokes scan_block() which may invoke a nomal printk() to print warning
> message. This can cause a deadlock in the scenario reported below:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(kmemleak_lock);
>                                lock(&port->lock);
>                                lock(kmemleak_lock);
>   lock(console_owner);
> 
> To solve this problem, switch to printk_safe mode before printing warning
> message, this will redirect all printk()-s to a special per-CPU buffer,
> which will be flushed later from a safe context (irq work), and this
> deadlock problem can be avoided. The proper API to use should be
> printk_deferred_enter()/printk_deferred_exit() if we want to deferred the
> printing [2].
> 
> This patch also fixes other similar case that need to use the printk
> deferring [3].
> 
> ...
>
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c

I'm not sure which kernel version this was against, but kmemleak.c has
changed quite a lot.

Could we please see a patch against a latest kernel version?  Linus
mainline will suit.

Thanks.