Re: [PATCH] can: j1939: fix potential race condition in BAM segmentation

[Oleksij Rempel <o.rempel@pengutronix.de>]

Hi,

On Thu, Oct 01, 2026 at 01:18:27PM +0200, Hölzl, Alexander wrote:
> Hello,
> Am 01.10.2026 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. Your
> > > 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 address
> sashiko comment's as well as the other patch I still have open.

Nice, thx.

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...

> Additionally while I'm at it I just wanted 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 is 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-cases.
> This especially true if one of the sessions is a BAM session transmitting a
> longer message, as there are 50ms pauses between each frame.

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.

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