• Yonghong Song's avatar
    bpf: fix rcu lockdep warning for lpm_trie map_free callback · 6c5f6102
    Yonghong Song authored
    Commit 9a3efb6b ("bpf: fix memory leak in lpm_trie map_free callback function")
    fixed a memory leak and removed unnecessary locks in map_free callback function.
    Unfortrunately, it introduced a lockdep warning. When lockdep checking is turned on,
    running tools/testing/selftests/bpf/test_lpm_map will have:
    
      [   98.294321] =============================
      [   98.294807] WARNING: suspicious RCU usage
      [   98.295359] 4.16.0-rc2+ #193 Not tainted
      [   98.295907] -----------------------------
      [   98.296486] /home/yhs/work/bpf/kernel/bpf/lpm_trie.c:572 suspicious rcu_dereference_check() usage!
      [   98.297657]
      [   98.297657] other info that might help us debug this:
      [   98.297657]
      [   98.298663]
      [   98.298663] rcu_scheduler_active = 2, debug_locks = 1
      [   98.299536] 2 locks held by kworker/2:1/54:
      [   98.300152]  #0:  ((wq_completion)"events"){+.+.}, at: [<00000000196bc1f0>] process_one_work+0x157/0x5c0
      [   98.301381]  #1:  ((work_completion)(&map->work)){+.+.}, at: [<00000000196bc1f0>] process_one_work+0x157/0x5c0
    
    Since actual trie tree removal happens only after no other
    accesses to the tree are possible, replacing
      rcu_dereference_protected(*slot, lockdep_is_held(&trie->lock))
    with
      rcu_dereference_protected(*slot, 1)
    fixed the issue.
    
    Fixes: 9a3efb6b ("bpf: fix memory leak in lpm_trie map_free callback function")
    Reported-by: default avatarEric Dumazet <edumazet@google.com>
    Suggested-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarYonghong Song <yhs@fb.com>
    Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
    Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    6c5f6102
lpm_trie.c 19.9 KB