From: Ivan Boule <ivan.boule@6wind.com>
To: Bruce Richardson <bruce.richardson@intel.com>,
"Ananyev, Konstantin" <konstantin.ananyev@intel.com>
Cc: Thomas Monjalon <thomas.monjalon@6wind.com>,
"Pattan, Reshma" <reshma.pattan@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH v9 1/8] ethdev: use locks to protect Rx/Tx callback lists
Date: Wed, 15 Jun 2016 16:07:20 +0200 [thread overview]
Message-ID: <57616118.7080806@6wind.com> (raw)
In-Reply-To: <20160615132928.GA11536@bricha3-MOBL3>
On 06/15/2016 03:29 PM, Bruce Richardson wrote:
> On Wed, Jun 15, 2016 at 12:40:16PM +0000, Ananyev, Konstantin wrote:
>> Hi Ivan,
>>
>>> -----Original Message-----
>>> From: Ivan Boule [mailto:ivan.boule@6wind.com]
>>> Sent: Wednesday, June 15, 2016 1:15 PM
>>> To: Thomas Monjalon; Ananyev, Konstantin
>>> Cc: Pattan, Reshma; dev@dpdk.org
>>> Subject: Re: [dpdk-dev] [PATCH v9 1/8] ethdev: use locks to protect Rx/Tx callback lists
>>>
>>> On 06/15/2016 10:48 AM, Thomas Monjalon wrote:
>>>
>>>>>
>>>>>> I think the read access would need locking but we do not want it
>>>>>> in fast path.
>>>>>
>>>>> I don't think it would be needed.
>>>>> As I said - read/write interaction didn't change from what we have right now.
>>>>> But if you have some particular scenario in mind that you believe would cause
>>>>> a race condition - please speak up.
>>>>
>>>> If we add/remove a callback during a burst? Is it possible that the next
>>>> pointer would have a wrong value leading to a crash?
>>>> Maybe we need a comment to state that we should not alter burst
>>>> callbacks while running burst functions.
>>>>
>>>
>>> Hi Reshma,
>>>
>>> You claim that the "rte_eth_rx_cb_lock" does not need to be hold in the
>>> function "rte_eth_rx_burst()" while parsing the "post_rx_burst_cbs" list
>>> of RX callbacks associated with the polled RX queue to safely remove RX
>>> callback(s) in parallel.
>>> The problem is not [only] with the setting and the loading of "cb->next"
>>> that you assume to be atomic operations, which is certainly true on most
>>> CPUs.
>>> I see the 2 important following issues:
>>>
>>> 1) the "rte_eth_rxtx_callback" data structure associated with a removed
>>> RX callback could still be accessed in the callback parsing loop of the
>>> function "rte_eth_rx_burst()" after having been freed in parallel.
>>>
>>> BUT SUCH A BAD SITUATION WILL NOT CURRENTLY HAPPEN, THANKS TO THE NICE
>>> MEMORY LEAK BUG in the function "rte_eth_remove_rx_callback()" that
>>> does not free the "rte_eth_rxtx_callback" data structure associated with
>>> the removed callback !
>>
>> Yes, though it is documented behaviour, someone can probably
>> refer it as a feature, not a bug ;)
>>
>
> +1
> This is definitely not a bug, this is absolutely by design. One may argue with
> the design, but it was done for a definite reason, so as to avoid paying the
> penalty of having locks. It pushes more responsibility onto the app, but it
> does allow the app to choose the best solution for managing the freeing of
> memory for its situation. The alternative is to force all apps to pay the cost
> of having locks, even if better options for freeing the memory are available.
>
> /Bruce
>
-1 (not to say 0xFFFFFFFF)
This is definitely an API design bug !
I would say that if you don't know how to free a resource that you
allocate, it is very likely that you are wrong allocating it.
And this is exactly what happens here with RX/TX callback data structures.
This problem can easily be addressed by just changing the API as follows:
Change
void *
rte_eth_add_rx_callback(uint8_t port_id, uint16_t queue_id,
rte_rx_callback_fn fn, void *user_param)
to
int
rte_eth_add_rx_callback(uint8_t port_id, uint16_t queue_id,
struct rte_eth_rxtx_callback *cb)
In addition of solving the problem, this approach makes the API
consistent and let the application allocate "rte_eth_rxtx_callback" data
structures through any appropriate mean.
Regards,
Ivan
--
Ivan Boule
6WIND Development Engineer
next prev parent reply other threads:[~2016-06-15 14:07 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1465487895-5870-1-git-send-email-reshma.pattan@intel.com>
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 0/8] add packet capture framework Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 1/8] librte_ether: protect add/remove of rxtx callbacks with spinlocks Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 2/8] librte_ether: add new api rte_eth_add_first_rx_callback Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 3/8] librte_ether: add new fields to rte_eth_dev_info struct Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 4/8] librte_ether: make rte_eth_dev_get_port_by_name rte_eth_dev_get_name_by_port public Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 5/8] lib/librte_pdump: add new library for packet capturing support Reshma Pattan
2016-06-10 18:48 ` Aaron Conole
2016-06-10 22:14 ` Pattan, Reshma
2016-06-13 13:28 ` Aaron Conole
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 6/8] app/pdump: add pdump tool for packet capturing Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 7/8] app/test-pmd: add pdump initialization uninitialization Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 8/8] doc: update doc for packet capture framework Reshma Pattan
2016-06-10 23:23 ` [dpdk-dev] [PATCH v8 0/8] add " Neil Horman
2016-06-13 8:47 ` Pattan, Reshma
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 " Reshma Pattan
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 1/8] ethdev: use locks to protect Rx/Tx callback lists Reshma Pattan
2016-06-14 19:59 ` Thomas Monjalon
2016-06-15 5:30 ` Pattan, Reshma
2016-06-15 8:19 ` Thomas Monjalon
2016-06-15 8:37 ` Ananyev, Konstantin
2016-06-15 8:48 ` Thomas Monjalon
2016-06-15 9:54 ` Ananyev, Konstantin
2016-06-15 11:17 ` Thomas Monjalon
2016-06-15 13:49 ` Thomas Monjalon
2016-06-15 12:15 ` Ivan Boule
2016-06-15 12:40 ` Ananyev, Konstantin
2016-06-15 13:29 ` Bruce Richardson
2016-06-15 14:07 ` Ivan Boule [this message]
2016-06-15 14:19 ` Bruce Richardson
2016-06-15 14:20 ` Ananyev, Konstantin
2016-06-15 14:22 ` Bruce Richardson
2016-06-15 14:27 ` Ananyev, Konstantin
2016-06-15 15:33 ` Ivan Boule
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 2/8] ethdev: add new api to add Rx callback as head of the list Reshma Pattan
2016-06-14 20:01 ` Thomas Monjalon
2016-06-14 21:43 ` Pattan, Reshma
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 3/8] ethdev: add new fields to ethdev info struct Reshma Pattan
2016-06-14 20:10 ` Thomas Monjalon
2016-06-14 21:57 ` Pattan, Reshma
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 4/8] ethdev: make get port by name and get name by port public Reshma Pattan
2016-06-14 20:23 ` Thomas Monjalon
2016-06-14 21:55 ` Pattan, Reshma
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 5/8] pdump: add new library for packet capturing support Reshma Pattan
2016-06-14 20:28 ` Thomas Monjalon
2016-06-14 21:59 ` Pattan, Reshma
2016-06-15 9:05 ` Mcnamara, John
2016-06-15 9:32 ` Thomas Monjalon
2016-06-15 9:43 ` Bruce Richardson
2016-06-15 15:44 ` Mcnamara, John
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 6/8] app/pdump: add pdump tool for packet capturing Reshma Pattan
2016-06-14 19:56 ` Thomas Monjalon
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 7/8] app/testpmd: add pdump initialization uninitialization Reshma Pattan
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 8/8] doc: update doc for packet capture framework Reshma Pattan
2016-06-14 20:41 ` Thomas Monjalon
2016-06-15 5:44 ` Pattan, Reshma
2016-06-15 8:24 ` Thomas Monjalon
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 0/7] add " Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 1/7] ethdev: use locks to protect Rx/Tx callback lists Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 2/7] ethdev: add new api to add Rx callback as head of the list Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 3/7] ethdev: add new fields to ethdev info struct Reshma Pattan
2016-06-16 19:14 ` Thomas Monjalon
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 4/7] ethdev: make get port by name and get name by port public Reshma Pattan
2016-06-16 20:27 ` Thomas Monjalon
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 5/7] pdump: add new library for packet capturing support Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 6/7] app/pdump: add pdump tool for packet capturing Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 7/7] app/testpmd: add pdump initialization uninitialization Reshma Pattan
2016-06-16 21:55 ` [dpdk-dev] [PATCH v10 0/7] add packet capture framework Thomas Monjalon
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