Re: [RFC PATCH 1/1] page_pool: do not release pool until inflight == 0.

["Jonathan Lemon" <jonathan.lemon@gmail.com>]

On 11 Nov 2019, at 1:21, Jesper Dangaard Brouer wrote:

> On Sun, 10 Nov 2019 22:20:38 -0800
> Jonathan Lemon <jonathan.lemon@gmail.com> wrote:
>
>> diff --git a/net/core/xdp.c b/net/core/xdp.c
>> index 20781ad5f9c3..e334fad0a6b8 100644
>> --- a/net/core/xdp.c
>> +++ b/net/core/xdp.c
>> @@ -70,25 +70,47 @@ static void __xdp_mem_allocator_rcu_free(struct 
>> rcu_head *rcu)
>>
>>  	xa = container_of(rcu, struct xdp_mem_allocator, rcu);
>>
>> -	/* Allocator have indicated safe to remove before this is called */
>> -	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
>> -		page_pool_free(xa->page_pool);
>> -
>>  	/* Allow this ID to be reused */
>>  	ida_simple_remove(&mem_id_pool, xa->mem.id);
>>
>> -	/* Poison memory */
>> -	xa->mem.id = 0xFFFF;
>> -	xa->mem.type = 0xF0F0;
>> -	xa->allocator = (void *)0xDEAD9001;
>> -
>>  	kfree(xa);
>>  }
>
> Can you PLEASE leave the memory poisonings that I have added alone.
> Removing these are irrelevant for current patch. You clearly don't 
> like
> this approach, but I've also clearly told that I disagree.  I'm the
> maintainer of this code and I prefer letting them stay. I'm the one
> that signed up for dealing with hard to find bugs in the code.

As you're the maintainer, I'll put this back.  However, I strongly
feel that this is poor practice; detecting use-after-free in cases
like this should be the job of the page and memory allocator; not
kmemleak (which detects lost memory), but page poisoning and redzone
support.

If this is really useful, it should specifically be under DEBUG
support, rather than in the mainline code.  It's not a performance
issue - just more techdebt, from my POV.
-- 
Jonathan