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

[Catalin Marinas <catalin.marinas@arm.com>]

On Wed, Aug 13, 2025 at 04:53:10PM +0800, Gu Bowen 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].
> 
> [1]
> https://lore.kernel.org/all/20250730094914.566582-1-gubowen5@huawei.com/
> [2]
> https://lore.kernel.org/all/5ca375cd-4a20-4807-b897-68b289626550@redhat.com/
> [3]
> https://lore.kernel.org/all/aJCir5Wh362XzLSx@arm.com/
> ====================
> 
> Cc: stable@vger.kernel.org # 5.10
> Signed-off-by: Gu Bowen <gubowen5@huawei.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>