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

From: Simon Horman <[email-masked]>
Date: Fri, 27 Mar 2026 11:20:56 +0000

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

> 
> Fixes: a806ad8ee2aa ("bridge: cfm: Kernel space implementation of CFM. CCM frame TX added.")
> Reported-by: Weiming Shi <[email-masked]>
> Signed-off-by: Xiang Mei <[email-masked]>

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