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

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

On Wed, 30 Jul 2025 17:49:14 +0800 Gu Bowen <gubowen5@huawei.com> wrote:

> 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.
> 
> Our syztester report the following lockdep error:
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.10.0-22221-gca646a51dd00 #16 Not tainted
> ------------------------------------------------------
> 
> ...
>
> Chain exists of:
>   console_owner --> &port->lock --> kmemleak_lock
> 
> Cc: stable@vger.kernel.org # 5.10
> Signed-off-by: Gu Bowen <gubowen5@huawei.com>
> ---
>  mm/kmemleak.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 4801751cb6b6..d322897a1de1 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -390,9 +390,11 @@ static struct kmemleak_object *lookup_object(unsigned long ptr, int alias)
>  		else if (object->pointer == ptr || alias)
>  			return object;
>  		else {
> +			__printk_safe_enter();
>  			kmemleak_warn("Found object by alias at 0x%08lx\n",
>  				      ptr);
>  			dump_object_info(object);
> +			__printk_safe_exit();
>  			break;
>  		}
>  	}

umm,

--- a/mm/kmemleak.c~a
+++ a/mm/kmemleak.c
@@ -103,6 +103,8 @@
 #include <linux/kmemleak.h>
 #include <linux/memory_hotplug.h>
 
+#include "../kernel/printk/internal.h"		/* __printk_safe_enter */
+
 /*
  * Kmemleak configuration and common defines.
  */


I'm not sure we're allowed to do that.  Is there an official way?