Re: [PATCH v2] mm: Fix possible deadlock in console_trylock_spinning

[Gu Bowen <gubowen5@huawei.com>]

On 8/7/2025 11:11 PM, Catalin Marinas wrote:
> 
>> @@ -433,8 +439,15 @@ static struct kmemleak_object *mem_pool_alloc(gfp_t gfp)
>>   		list_del(&object->object_list);
>>   	else if (mem_pool_free_count)
>>   		object = &mem_pool[--mem_pool_free_count];
>> -	else
>> +	else {
>> +		/*
>> +		 * Printk deferring due to the kmemleak_lock held.
>> +		 * This is done to avoid deadlock.
>> +		 */
>> +		printk_deferred_enter();
>>   		pr_warn_once("Memory pool empty, consider increasing CONFIG_DEBUG_KMEMLEAK_MEM_POOL_SIZE\n");
>> +		printk_deferred_exit();
>> +	}
>>   	raw_spin_unlock_irqrestore(&kmemleak_lock, flags);
> 
> I wouldn't bother with printk deferring here, just set a bool warn
> variable and report it after unlocking. We recently merged another patch
> that does this.
> 

That's fine, I will send another patch that does not include this part.

>>   
>>   	return object;
>> @@ -632,6 +645,11 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
>>   		else if (parent->pointer + parent->size <= ptr)
>>   			link = &parent->rb_node.rb_right;
>>   		else {
>> +			/*
>> +			 * Printk deferring due to the kmemleak_lock held.
>> +			 * This is done to avoid deadlock.
>> +			 */
>> +			printk_deferred_enter();
>>   			kmemleak_stop("Cannot insert 0x%lx into the object search tree (overlaps existing)\n",
>>   				      ptr);
>>   			/*
>> @@ -639,6 +657,7 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
>>   			 * be freed while the kmemleak_lock is held.
>>   			 */
>>   			dump_object_info(parent);
>> +			printk_deferred_exit();
> 
> This is part of __link_object(), called with the lock held, so easier to
> defer the printing as above.
> 
> BTW, the function names in the diff don't match mainline. Which kernel
> version is this patch based on?
> 
The kernel version of this patch is stable-5.10. This part of the code 
exists in function __link_object() in the mainline.