bpf: lru: Fix unintended eviction when updating lru hash maps #6629
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The hash field is not used by the LRU list itself. Setting hash while manipulating the LRU list also obscures the intent of the code and makes it harder to follow. Tidy this up by moving the hash assignment to prealloc_lru_pop(), where the element is prepared for insertion into the hash table. Signed-off-by: Leon Hwang <[email protected]>
Introduce the helper bpf_lru_node_reset_state to set type and clear ref. No functional change intended. Signed-off-by: Leon Hwang <[email protected]>
It's to update the 'next_inactive_rotation' for extra node case using the helper. No functional change intended. Signed-off-by: Leon Hwang <[email protected]>
When updating an existing element in lru_[percpu_,]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 using the extra lru node without triggering any eviction. Fixes: 29ba732 ("bpf: Add BPF_MAP_TYPE_LRU_HASH") Fixes: 8f84493 ("bpf: Add BPF_MAP_TYPE_LRU_PERCPU_HASH") Signed-off-by: Leon Hwang <[email protected]>
…ng lru_[percpu_,]hash maps Add four 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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Pull request for series with
subject: bpf: lru: Fix unintended eviction when updating lru hash maps
version: 3
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1039475