On 11.05.2022 15:24:00, Oliver Hartkopp wrote: > > Another use where skb->sk breaks is sending CAN frames with SO_TXTIME > > with the sched_etf. > > > > I have a patched version of cangen that uses SO_TXTIME. It attaches a > > time to transmit to a CAN frame when sending it. If you send 10 frames, > > each 100ms after the other and then exit the program, the first CAN > > frames show up as TX'ed while the others (after closing the socket) show > > up as RX'ed CAN frames in candump. > > Hm, this could be an argument for the origin flag. > > But I'm more scared about your described behaviour. What happens if > the socket is still open? SO_TXTIME makes an existing race window really, really, really wide. The race window is between sendmsg() returning to user space and can_put_echo_skb() -> can_create_echo_skb() -> can_skb_set_owner(). In can_skb_set_owner() a reference to the socket is taken, if the socket is not closed: | https://elixir.bootlin.com/linux/v5.17.6/source/include/linux/can/skb.h#L75 If the socket closes _after_ sendmsg(), but _before_ the driver calls can_put_echo_skb() the CAN frame will have no socket reference and show up as RX'ed. > There obviously must be some instance removing the sk reference, right?? No. That's all fine. We fixes that in: | https://lore.kernel.org/all/20210226092456.27126-1-o.rempel@xxxxxxxxxxxxxx/ 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 |
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