Re: [PATCH net] bridge: cfm: do not reschedule TX work when interval is zero

On Fri, Mar 27, 2026 at 4:21 AM Simon Horman <[email protected]> wrote:
>
> On Wed, Mar 25, 2026 at 08:19:57PM -0700, Xiang Mei wrote:
> > ccm_tx_work_expired() uses interval_to_us() to convert the configured
> > exp_interval enum into a microsecond delay, then passes it to
> > queue_delayed_work() to schedule the next iteration. The ccm_tx_dwork
> > callback re-arms the same delayed_work struct at the end of each
> > invocation, forming a repeating timer.
> >
> > interval_to_us() returns 0 for BR_CFM_CCM_INTERVAL_NONE and any
> > out-of-range enum value. When this 0 is passed to queue_delayed_work()
> > as the delay, the work item fires immediately and re-arms itself with
> > zero delay again, creating an infinite tight loop. Each iteration
> > allocates an skb via ccm_frame_build() and queues it for transmission.
> > The skbs pile up faster than the network stack can free them because the
> > worker never yields the CPU, rapidly exhausting all kernel memory until
> > OOM deadlock panic.
> >
> > Since CC config and CCM TX are independent netlink commands that can be
> > issued in any order, there is no single configuration entry point where
> > rejecting interval=0 would cover all cases.
> >
> > Fix this by checking the interval at the start of ccm_tx_work_expired()
> > and stopping transmission immediately if it is zero. Set period to 0 so
> > that br_cfm_cc_ccm_tx() correctly sees transmission as stopped and can
> > restart it later if a valid interval is configured. This also avoids
> > transmitting a CCM frame with an invalid interval value.
>
> Hi,
>
> I think that the principle should be that code that doesn't need
> to be in the datapath shouldn't be in the datapath.
>
> So, with that in mind, I think it would be better to set a lower bound on
> exp_interval when the mep is:
>
> a) Created. It looks like that happens in br_cfm_mep_create
> b) Configured. It looks like that can be done by setting a policy on the
>    minimum value of IFLA_BRIDGE_CFM_CC_CONFIG_EXP_INTERVAL
>
Thanks for the suggestion. You are right, it's better to move the
check out of the datapath. V2 has been sent, which blocks the invalid
interval in creation/configuration.
> >
> > Fixes: a806ad8ee2aa ("bridge: cfm: Kernel space implementation of CFM. CCM frame TX added.")
> > Reported-by: Weiming Shi <[email protected]>
> > Signed-off-by: Xiang Mei <[email protected]>
>
> ...