From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Vincent MAILHOL <mailhol.vincent@wanadoo.fr>,
Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Jakub Kicinski <kuba@kernel.org>,
Eric Dumazet <edumazet@google.com>,
netdev <netdev@vger.kernel.org>,
David Miller <davem@davemloft.net>,
linux-can <linux-can@vger.kernel.org>,
kernel@pengutronix.de
Subject: Re: [net 05/27] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context
Date: Thu, 5 Nov 2020 08:44:31 +0100 [thread overview]
Message-ID: <02c5f3c7-7b6a-a487-39fc-50b5fad0eebc@pengutronix.de> (raw)
In-Reply-To: <CAMZ6RqK=oEn3pgHb2byMC_SOVdG3Bbsfzssu9Fd-jDpSzEbrwQ@mail.gmail.com>
[-- Attachment #1.1: Type: text/plain, Size: 2236 bytes --]
On 11/5/20 5:47 AM, Vincent MAILHOL wrote:
>>> Okay, we can take this as a quick fix but to me it seems a little
>>> strange to be dropping what is effectively locally generated frames.
>
> For those who are not familiar with SocketCAN and to make sure that we
> are all aligned here, let me give a bit of context of how the echo on CAN
> skbs is usually implement in the drivers:
> * In the xmit() branch, the driver would queue the skb using
> can_put_echo_skb().
> * Whenever the driver gets notified of a successful TX, it will loopback
> the skb using can_get_echo_skb().
>
> This is why the loopback is usually done in hardware IRQ context (but
> drivers are also free to skip the second step and directly loopback the
> skb in the xmit() branch).
>
>> Thanks! So this patch doesn't hinder Marc's PR :-)
>>
>>> Can we use a NAPI poll model here and back pressure TX if the echo
>>> is not keeping up?
>>
>> Some of the CAN network drivers already support NAPI.
And some drivers (i.e. flexcan and mcp251xfd) already queue the ech_skb via NAPI.
> I had a quick look at NAPI in the past and my understanding is that it
> requires the ability to turn off hardware interrupts meaning that it can
> be only used on some NIC, not but not, for example, on USB devices.
>
> It would be nice to extend the NAPI with skb loopback for drivers which
> already supports it but I am not sure how to include the other drivers.
>
>> @Marc: Can we also use NAPI for echo'ing the skbs?
The flexcan driver does:
https://elixir.bootlin.com/linux/v5.10-rc2/source/drivers/net/can/flexcan.c#L1080
In the interrupt handler, the driver pushes the echo_skb into the rx-offload
queue and triggers NAPI. The rx-offload pushed the skb into the networking stack
via NAPI.
Here the code in the mcp251xfd driver:
https://elixir.bootlin.com/linux/v5.10-rc2/source/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c#L1237
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
next prev parent reply other threads:[~2020-11-05 7:44 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-03 22:06 pull-request: can 2020-11-03 Marc Kleine-Budde
2020-11-03 22:06 ` [net 01/27] dt-bindings: can: add can-controller.yaml Marc Kleine-Budde
2020-11-03 22:06 ` [net 02/27] dt-bindings: can: flexcan: convert fsl,*flexcan bindings to yaml Marc Kleine-Budde
2020-11-03 22:06 ` [net 03/27] can: proc: can_remove_proc(): silence remove_proc_entry warning Marc Kleine-Budde
2020-11-03 22:06 ` [net 04/27] can: rx-offload: don't call kfree_skb() from IRQ context Marc Kleine-Budde
2020-11-03 22:06 ` [net 05/27] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard " Marc Kleine-Budde
2020-11-04 1:21 ` Jakub Kicinski
2020-11-04 4:29 ` Vincent MAILHOL
2020-11-04 8:16 ` Eric Dumazet
2020-11-04 14:59 ` Oliver Hartkopp
2020-11-04 16:02 ` Jakub Kicinski
2020-11-04 17:46 ` Oliver Hartkopp
2020-11-05 4:47 ` Vincent MAILHOL
2020-11-05 7:44 ` Marc Kleine-Budde [this message]
2020-11-03 22:06 ` [net 06/27] can: dev: __can_get_echo_skb(): fix real payload length return value for RTR frames Marc Kleine-Budde
2020-11-03 22:06 ` [net 07/27] can: can_create_echo_skb(): fix echo skb generation: always use skb_clone() Marc Kleine-Budde
2020-11-03 22:06 ` [net 08/27] can: j1939: rename jacd tool Marc Kleine-Budde
2020-11-03 22:06 ` [net 09/27] can: j1939: fix syntax and spelling Marc Kleine-Budde
2020-11-03 22:06 ` [net 10/27] can: j1939: swap addr and pgn in the send example Marc Kleine-Budde
2020-11-03 22:06 ` [net 11/27] can: j1939: use backquotes for code samples Marc Kleine-Budde
2020-11-03 22:06 ` [net 12/27] can: j1939: j1939_sk_bind(): return failure if netdev is down Marc Kleine-Budde
2020-11-03 22:06 ` [net 13/27] can: isotp: Explain PDU in CAN_ISOTP help text Marc Kleine-Budde
2020-11-03 22:06 ` [net 14/27] can: isotp: isotp_rcv_cf(): enable RX timeout handling in listen-only mode Marc Kleine-Budde
2020-11-03 22:06 ` [net 15/27] can: isotp: padlen(): make const array static, makes object smaller Marc Kleine-Budde
2020-11-03 22:06 ` [net 16/27] can: ti_hecc: ti_hecc_probe(): add missed clk_disable_unprepare() in error path Marc Kleine-Budde
2020-11-03 22:06 ` [net 17/27] can: xilinx_can: handle failure cases of pm_runtime_get_sync Marc Kleine-Budde
2020-11-03 22:06 ` [net 18/27] can: peak_usb: add range checking in decode operations Marc Kleine-Budde
2020-11-03 22:06 ` [net 19/27] can: peak_usb: peak_usb_get_ts_time(): fix timestamp wrapping Marc Kleine-Budde
2020-11-03 22:06 ` [net 20/27] can: peak_canfd: pucan_handle_can_rx(): fix echo management when loopback is on Marc Kleine-Budde
2020-11-03 22:06 ` [net 21/27] can: mcp251xfd: mcp251xfd_regmap_crc_read(): increase severity of CRC read error messages Marc Kleine-Budde
2020-11-05 16:24 ` Manivannan Sadhasivam
2020-11-05 16:39 ` Marc Kleine-Budde
2020-11-05 18:14 ` Manivannan Sadhasivam
2020-11-06 8:35 ` Marc Kleine-Budde
2020-11-03 22:06 ` [net 22/27] can: mcp251xfd: mcp251xfd_regmap_nocrc_read(): fix semicolon.cocci warnings Marc Kleine-Budde
2020-11-03 22:06 ` [net 23/27] can: mcp251xfd: remove unneeded break Marc Kleine-Budde
2020-11-03 22:06 ` [net 24/27] can: flexcan: remove FLEXCAN_QUIRK_DISABLE_MECR quirk for LS1021A Marc Kleine-Budde
2020-11-03 22:06 ` [net 25/27] can: flexcan: add ECC initialization for LX2160A Marc Kleine-Budde
2020-11-03 22:06 ` [net 26/27] can: flexcan: add ECC initialization for VF610 Marc Kleine-Budde
2020-11-03 22:06 ` [net 27/27] can: flexcan: flexcan_remove(): disable wakeup completely Marc Kleine-Budde
2020-11-04 18:43 ` pull-request: can 2020-11-03 Jakub Kicinski
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=02c5f3c7-7b6a-a487-39fc-50b5fad0eebc@pengutronix.de \
--to=mkl@pengutronix.de \
--cc=davem@davemloft.net \
--cc=edumazet@google.com \
--cc=kernel@pengutronix.de \
--cc=kuba@kernel.org \
--cc=linux-can@vger.kernel.org \
--cc=mailhol.vincent@wanadoo.fr \
--cc=netdev@vger.kernel.org \
--cc=socketcan@hartkopp.net \
/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).