From: Jakub Kicinski <kuba@kernel.org>
To: Liang Chen <liangchen.linux@gmail.com>
Cc: ilias.apalodimas@linaro.org, edumazet@google.com,
hawk@kernel.org, davem@davemloft.net, pabeni@redhat.com,
netdev@vger.kernel.org, alexander.duyck@gmail.com,
linyunsheng@huawei.com
Subject: Re: [PATCH v3] skbuff: Fix a race between coalescing and releasing SKBs
Date: Wed, 12 Apr 2023 21:08:16 -0700 [thread overview]
Message-ID: <20230412210816.072b5fe3@kernel.org> (raw)
In-Reply-To: <20230411022640.8453-1-liangchen.linux@gmail.com>
On Tue, 11 Apr 2023 10:26:40 +0800 Liang Chen wrote:
> /* In general, avoid mixing slab allocated and page_pool allocated
> - * pages within the same SKB. However when @to is not pp_recycle and
> - * @from is cloned, we can transition frag pages from page_pool to
> - * reference counted.
> - *
> - * On the other hand, don't allow coalescing two pp_recycle SKBs if
> - * @from is cloned, in case the SKB is using page_pool fragment
> - * references (PP_FLAG_PAGE_FRAG). Since we only take full page
> - * references for cloned SKBs at the moment that would result in
> - * inconsistent reference counts.
> + * pages within the same SKB. However don't allow coalescing two
The word 'however' no longer works here because there's no
contradiction, it's an additional rule.
> + * pp_recycle SKBs if @from is cloned, in case the SKB is using
> + * page_pool fragment references (PP_FLAG_PAGE_FRAG). Since we only
> + * take full page references for cloned SKBs at the moment that would
> + * result in inconsistent reference counts.
> */
> - if (to->pp_recycle != (from->pp_recycle && !skb_cloned(from)))
> + if (to->pp_recycle != from->pp_recycle ||
> + (from->pp_recycle && skb_cloned(from)))
How about we change the comment to:
/* In general, avoid mixing page_pool and non-page_pool allocated
* pages within the same SKB. Additionally avoid dealing with clones
* containing page_pool pages, in case the SKB is using page_pool fragment
* references (PP_FLAG_PAGE_FRAG). Since we only take full page
* references for cloned SKBs at the moment that would result in
* inconsistent reference counts.
* In theory we could take full references if from is cloned and
* !@to->pp_recycle but its tricky (due to potential race with the clone
* disappearing) and rare, so not worth dealing with.
*/
Please also add:
Fixes: 53e0961da1c7 ("page_pool: add frag page recycling support in page pool")
and Eric's review tag.
prev parent reply other threads:[~2023-04-13 4:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-11 2:26 [PATCH v3] skbuff: Fix a race between coalescing and releasing SKBs Liang Chen
2023-04-12 14:04 ` Eric Dumazet
2023-04-13 4:08 ` Jakub Kicinski [this message]
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