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Thunderbird Subject: Re: [PATCH] can: j1939: fix potential race condition in BAM segmentation To: Oleksij Rempel Cc: Marc Kleine-Budde , Markus Koeniger , robin@protonic.nl, linux-kernel@vger.kernel.org, kernel@pengutronix.de, linux-can@vger.kernel.org References: <20260610090619.70626-1-alexander.hoelzl@gmx.net> <20261001-bison-of-undeniable-art-5bcb84-mkl@pengutronix.de> <9da1ca76-4c89-4109-ba78-c08cfe69ea19@gmx.net> Content-Language: en-US From: =?UTF-8?Q?H=C3=B6lzl=2C_Alexander?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:Vezb9FmUeLGeBT+85rYVFr45SwevobX6KK3JSWn+7J0X4oe2lRs gXSTkGI4i6B3ghBMJefBb4Gd7bUJGtWz7OKuTRKZEoq66G+zu12AjK0x/WioiXbgnPQhLMF 6jgQdsnwxA0VrRMqvEzk8n87wQL3Q9bB9QHUWjjG81bekptg8BK4EwoGUy5/5+h7uZGxrfv Ji2UhkyX/HyWZtB4uv+HA== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:2XZvFp5n9jg=;6whI5/EBDtkKEQCcFa2PUAoE1C2 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um 12:57 schrieb Marc Kleine-Budde: >>> On 01.10.2026 12:42:21, Markus Koeniger wrote: >>>> I really appreciate your solution to schedule the TX timer for a BAM >>>> transfer after receiving the looped-back frame. >>> >> Glad that I could help. >> >>>> We use external CAN controllers in our system, which introduce some >>>> jitter into the transmit path. As a result, messages were sent from >>>> time to time too quickly and violated the 50 ms minimum interval. You= r >>>> patch solves this problem. >>>> >>>> Tested-by: Markus Koeniger markus.koeniger@liebherr.com >>> >>> Thanks for testing, however I'm not sure if we can get this patch >>> upstream if sashiko complains about it. >>> >> I wasn't planning on letting this patch stall. Next week I'll try to ad= dress >> sashiko comment's as well as the other patch I still have open. >=20 > Nice, thx. >=20 > I'm working right now on j1939 selftests for core functionality. Hope > it will be ready this week. If not, next week i'll be in Prag on E-OSS > conference... >=20 Ah that's good to know. In the CTS hold patch I've also implemented=20 some tests (https://lkml.org/lkml/2026/7/7/85) but I guess they'll=20 mostly be superfluous then?>> Additionally while I'm at it I just wanted= =20 to ask, is it intended behavior >> that the kernel implementation strictly serializes all J1939 sessions. = E.g >> when sending a segmented message directed to destination address A it i= s not >> possible to have a second session open targeting destination address B. >> According to the standard this is allowed and not >> being able to do so can result in very low performance in some use-case= s. >> This especially true if one of the sessions is a BAM session transmitti= ng a >> longer message, as there are 50ms pauses between each frame. >=20 > Is it not working with a separate socket? If I remember it correctly, > this behavior should be supported if two sockets send to separate > addresses. Withing one socket, frames should be serialized. >=20 I've never tried it with multiple sockets but if you say so I'm sure=20 it'll work :). For my use case specifically this quite inconvenient=20 behavior but I guess I might be abusing the stack a little bit :). I've written a patch which allows interleaved tx-sessions per socket but= =20 if the kernel behaves as designed then that's probably not something=20 which I should try to get into the mainline.