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javierhonduco / lightswitch

CPU profiler for Linux written in Rust
MIT License
7 stars 3 forks source link

tests: Fix off-by-32 bits in LPM tree #29

Closed javierhonduco closed 6 months ago

javierhonduco commented 6 months ago

The integration tests started failing starting with kernel 6.8, and after some checks, it pointed to this commit https://github.com/torvalds/linux/commit/9b75dbeb36fcd9fc7ed51d370310d0518a387769.

The tests fail now because the prefix length we pass is 32 bits higher (see initialiser) than the maximum prefix length. After this commit was introduced, any prefix length that's higher than the key size will return NULL earlier, rather than returning the value with the longest match, even if it's beyond the size the key can encode.

Test Plan

Ran the tests and some profiles on a box running 6.8.7-200 (Fedora) without issues.

Also added an assertion to ensure that the prefix_len is not bigger than the LPM trie key size.

javierhonduco commented 6 months ago

Many thanks to @florianl for noting that this was not a kernel regression, but a bug on my code!