Re: [PATCH net 2/3] net: tls: Cancel RX async resync request on rdc_delta overflow

[Sabrina Dubroca <sd@queasysnail.net>]

2025-09-22, 10:16:21 +0300, Shahar Shitrit wrote:
> 
> 
> On 12/09/2025 18:14, Sabrina Dubroca wrote:
> > 2025-09-10, 09:47:40 +0300, Tariq Toukan wrote:
> >> From: Shahar Shitrit <shshitrit@nvidia.com>
> >>
> >> When a netdev issues an RX async resync request, the TLS module
> >> increments rcd_delta for each new record that arrives. This tracks
> >> how far the current record is from the point where synchronization
> >> was lost.
> >>
> >> When rcd_delta reaches its threshold, it indicates that the device
> >> response is either excessively delayed or unlikely to arrive at all
> >> (at that point, tcp_sn may have wrapped around, so a match would no
> >> longer be valid anyway).
> >>
> >> Previous patch introduced tls_offload_rx_resync_async_request_cancel()
> >> to explicitly cancel resync requests when a device response failure
> >> is detected.
> >>
> >> This patch adds a final safeguard: cancel the async resync request when
> >> rcd_delta crosses its threshold, as reaching this point implies that
> >> earlier cancellation did not occur.
> >>
> >> Signed-off-by: Shahar Shitrit <shshitrit@nvidia.com>
> >> Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
> >> ---
> >>  net/tls/tls_device.c | 5 ++++-
> >>  1 file changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
> >> index f672a62a9a52..56c14f1647a4 100644
> >> --- a/net/tls/tls_device.c
> >> +++ b/net/tls/tls_device.c
> >> @@ -721,8 +721,11 @@ tls_device_rx_resync_async(struct tls_offload_resync_async *resync_async,
> >>  		/* shouldn't get to wraparound:
> >>  		 * too long in async stage, something bad happened
> >>  		 */
> >> -		if (WARN_ON_ONCE(resync_async->rcd_delta == USHRT_MAX))
> >> +		if (WARN_ON_ONCE(resync_async->rcd_delta == USHRT_MAX)) {
> > 
> > Do we still need to WARN here? It's a condition that can actually
> > happen (even if it's rare), and that the stack can handle, so maybe
> > not?
> > 
> You are right that now the stack handles this, but removing the WARN
> without any alternative, will remove any indication that something went
> wrong and will prevent us from improving by searching the error flow
> where we didn't cancel the request before reaching here. We can maybe
> replace the WARN with a counter. what do you think?

Do you use CONFIG_DEBUG_NET in your devel/test kernels? If so,
DEBUG_NET_WARN_ONCE would be an option. Or is it more so that
users/customers can report the problem (ie on production kernels
without CONFIG_DEBUG_NET) - in that case, the counter would work
better.
But if you really think that this condition indicates a driver bug,
maybe the WARN is still appropriate. Jakub, what do you think?


BTW, I was also thinking that the documentation
(Documentation/networking/tls-offload.rst) could maybe be improved a
bit with a description of how async resync works and how the driver is
expected to use the tls_offload_rx_resync_async_request_{start,end}
(and now _cancel) helpers. The section on "Stream scan
resynchronization" is pretty abstract.

-- 
Sabrina