From: Ivan Boule <ivan.boule@6wind.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>,
"Ananyev, Konstantin" <konstantin.ananyev@intel.com>
Cc: "Pattan, Reshma" <reshma.pattan@intel.com>, 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 14:15:09 +0200 [thread overview]
Message-ID: <576146CD.8060008@6wind.com> (raw)
In-Reply-To: <2907169.iIEIeOfXh7@xps13>
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 !
2) As a consequence of 1), RX callbacks can be invoked/executed
while/after being removed.
If the application must free resources that it dynamically allocated to
be used by the RX callback being removed, how to guarantee that the last
invocation of that RX callback has been completed and that such a
callback will never be invoked again, so that the resources can safely
be freed?
This is an example of a well-known more generic object deletion problem
which must arrange to guarantee that a deleted object is not used and
not accessible for use anymore before being actually deleted (freed, for
instance).
Note that a lock cannot be used in the execution path of the
rte_eth_rx_burst() function to address this issue, as locks MUST NEVER
be introduced in the RX/TX path of the DPDK framework.
Of course, the same issues stand for TX callbacks.
Regards,
Ivan
--
Ivan Boule
6WIND Development Engineer
next prev parent reply other threads:[~2016-06-15 12:15 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 [this message]
2016-06-15 12:40 ` Ananyev, Konstantin
2016-06-15 13:29 ` Bruce Richardson
2016-06-15 14:07 ` Ivan Boule
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=576146CD.8060008@6wind.com \
--to=ivan.boule@6wind.com \
--cc=dev@dpdk.org \
--cc=konstantin.ananyev@intel.com \
--cc=reshma.pattan@intel.com \
--cc=thomas.monjalon@6wind.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).