Re: [PATCH bpf-next v4 3/3] bpf, arena: check range_tree_set return in arena_free_pages and arena_free_worker

> bpf, arena: check range_tree_set return in arena_free_pages and arena_free_worker
>
> arena_free_pages() and arena_free_worker() now handle range_tree_set()
> errors. arena_free_pages() aborts the free on error, and
> arena_free_worker() moves range_tree_set() before PTE clearing so that a
> failed tree update leaves the PTEs intact instead of freeing pages that
> the arena free tree does not track.
>
> Also check the range_tree_set() return value in arena_alloc_pages()'s
> error path, which restores the unpopulated tail of a partially allocated
> range; log a warning instead of silently leaking the virtual range when
> the tree update fails.
>
> range_tree_set() is failure-atomic (it pre-allocates the node before
> touching the tree), so on -ENOMEM the range stays tracked as allocated
> and the pages remain mapped and accessible. A failed free is therefore
> retryable, and arena_map_free() reclaims any retained pages at map
> destruction; aborting the free avoids clearing PTEs for pages the arena
> free tree does not track.
>
> In arena_free_worker() a failed tree update used to leave the span in
> the drained list, where the second loop would still flush TLB entries,
> zap user VMAs, and free the span itself: the free request was dropped,
> user mappings were destroyed for a free that never happened, and the
> pages stayed mapped until map destruction. Keep failed spans on
> arena->free_spans instead and retry them on a later worker run; only
> spans whose PTE clearing actually ran are flushed, zapped, and released.
>
> Suggested-by: Emil Tsalapatis <[email protected]>
> Signed-off-by: Yuan Chen <[email protected]>

This looks like a bug fix for error handling in the arena code introduced
in an earlier commit. Should this include a Fixes: tag pointing to:

  Fixes: dc11a4dba246 ("bpf: Recover arena kernel faults with scratch page")


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