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Felix Maurer
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JIRA: https://issues.redhat.com/browse/RHEL-40917 JIRA: https://issues.redhat.com/browse/RHEL-146811 commit aae9d6b616b5e4ad8bbb82aa3661baa1522684d2 Author: Felix Maurer <fmaurer@redhat.com> Date: Thu Feb 5 14:57:33 2026 +0100 hsr: Implement more robust duplicate discard for HSR The HSR duplicate discard algorithm had even more basic problems than the described for PRP in the previous patch. It relied only on the last received sequence number to decide if a new frame should be forwarded to any port. This does not work correctly in any case where frames are received out of order. The linked bug report claims that this can even happen with perfectly fine links due to the order in which incoming frames are processed (which can be unexpected on multi-core systems). The issue also occasionally shows up in the HSR selftests. The main reason is that the sequence number that was last forwarded to the master port may have skipped a number which will in turn never be delivered to the host. As the problem (we accidentally skip over a sequence number that has not been received but will be received in the future) is similar to PRP, we can apply a similar solution. The duplicate discard algorithm based on the "sparse bitmap" works well for HSR if it is extended to track one bitmap for each port (A, B, master, interlink). To do this, change the sequence number blocks to contain a flexible array member as the last member that can keep chunks for as many bitmaps as we need. This design makes it easy to reuse the same algorithm in a potential PRP RedBox implementation. The duplicate discard algorithm functions are modified to deal with sequence number blocks of different sizes and to correctly use the array of bitmap chunks. There is a notable speciality for HSR: the port type has a special port type NONE with value 0. This leads to the number of port types being 5 instead of actually 4. To save memory, remove the NONE port from the bitmap (by subtracting 1) when setting up the block buffer and when accessing the bitmap chunks in the array. Removing the old algorithm allows us to get rid of a few fields that are not needed any more: time_out and seq_out for each port. We can also remove some functions that were only necessary for the previous duplicate discard algorithm. The removal of seq_out is possible despite its previous usage in hsr_register_frame_in: it was used to prevent updates to time_in when "invalid" sequence numbers were received. With the new duplicate discard algorithm, time_in has no relevance for the expiry of sequence numbers anymore. They will expire based on the timestamps in the sequence number blocks after at most 400ms. There is no need that a node "re-registers" to "resume communication": after 400ms, all sequence numbers are accepted again. Also, according to the IEC 62439-3:2021, all nodes are supposed to send no traffic for 500ms after boot to lead exactly to this expiry of seen sequence numbers. time_in is still used for pruning nodes from the node table after no traffic has been received for 60sec. Pruning is only needed if the node is really gone and has not been sending any traffic for that period. seq_out was also used to report the last incoming sequence number from a node through netlink. I am not sure how useful this value is to userspace at all, but added getting it from the sequence number blocks. This number can be outdated after node merging until a new block has been added. Update the KUnit test for the PRP duplicate discard so that the node allocation matches and expectations on the removed fields are removed. Reported-by: Yoann Congal <yoann.congal@smile.fr> Closes: https://lore.kernel.org/netdev/7d221a07-8358-4c0b-a09c-3b029c052245@smile.fr/ Signed-off-by: Felix Maurer <fmaurer@redhat.com> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://patch.msgid.link/36dc3bc5bdb7e68b70bb5ef86f53ca95a3f35418.1770299429.git.fmaurer@redhat.com Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Felix Maurer <fmaurer@redhat.com>