netdev - Re: [PATCH v2 0/4] bugfix: Introduce sendpages_ok() to check sendpage

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Date: Mon, 3 Jun 2024 11:07:57 +0200
From: Hannes Reinecke <hare@...e.de>
To: Jakub Kicinski <kuba@...nel.org>, Ofir Gal <ofir.gal@...umez.com>
Cc: davem@...emloft.net, linux-block@...r.kernel.org,
 linux-nvme@...ts.infradead.org, netdev@...r.kernel.org,
 ceph-devel@...r.kernel.org, dhowells@...hat.com, edumazet@...gle.com,
 pabeni@...hat.com, kbusch@...nel.org, axboe@...nel.dk, hch@....de,
 sagi@...mberg.me, philipp.reisner@...bit.com, lars.ellenberg@...bit.com,
 christoph.boehmwalder@...bit.com, idryomov@...il.com, xiubli@...hat.com
Subject: Re: [PATCH v2 0/4] bugfix: Introduce sendpages_ok() to check
 sendpage_ok() on contiguous pages

On 6/2/24 00:34, Jakub Kicinski wrote:
> On Thu, 30 May 2024 17:24:10 +0300 Ofir Gal wrote:
>> skbuff: before sendpage_ok - i: 0. page: 0x654eccd7 (pfn: 120755)
>> skbuff: before sendpage_ok - i: 1. page: 0x1666a4da (pfn: 120756)
>> skbuff: before sendpage_ok - i: 2. page: 0x54f9f140 (pfn: 120757)
> 
> noob question, how do you get 3 contiguous pages, the third of which
> is slab? is_slab doesn't mean what I think it does, or we got extremely
> lucky with kmalloc?
> 
I guess it's not slab which triggered; the actual code is:

static inline bool sendpage_ok(struct page *page)
{
         return !PageSlab(page) && page_count(page) >= 1;
}

My bet is on 'page_count()' triggering.

Cheers,

Hannes