bpf: Fix unintended eviction when updating lru hash maps #6449
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When updating an existing element in lru_hash maps, the current implementation always calls prealloc_lru_pop() to get a new node before checking if the key already exists. If the map is full, this triggers LRU eviction and removes an existing element, even though the update operation only needs to modify the value of an existing key in-place. This is problematic because: 1. Users may unexpectedly lose entries when doing simple value updates 2. The eviction overhead is unnecessary for existing key updates Fix this by first checking if the key exists before allocating a new node. If the key is found, update the value in-place, refresh the LRU reference, and return immediately without triggering any eviction. Fixes: 29ba732 ("bpf: Add BPF_MAP_TYPE_LRU_HASH") Signed-off-by: Leon Hwang <[email protected]>
Similar to the previous fix for lru_hash maps, the lru_percpu_hash map implementation also suffers from unnecessary eviction when updating existing elements. When updating a key that already exists in a full lru_percpu_hash map, the current code path calls prealloc_lru_pop() before checking for the existing key (unless map_flags is BPF_EXIST). This can evict an unrelated element even though the update is just modifying the per-CPU value of an existing entry. Fix this by looking up the key first. If found, update the per-CPU value in-place using pcpu_copy_value(), refresh the LRU reference, and return early. Only proceed with node allocation if the key does not exist. Fixes: 8f84493 ("bpf: Add BPF_MAP_TYPE_LRU_PERCPU_HASH") Signed-off-by: Leon Hwang <[email protected]>
…ng lru hash maps Add two tests to verify that updating an existing element in LRU hash maps does not cause unintended eviction of other elements. The test creates lru_hash/lru_percpu_hash maps with max_entries slots and populates all of them. It then updates an existing key and verifies that: 1. The update succeeds without error 2. The updated key has the new value 3. All other keys still exist with their original values This validates the fix that prevents unnecessary LRU eviction when updating existing elements in full LRU hash maps. Signed-off-by: Leon Hwang <[email protected]>
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Upstream branch: ff34657 |
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1029765 expired. Closing PR. |
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Pull request for series with
subject: bpf: Fix unintended eviction when updating lru hash maps
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1029765