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    Subject[PATCH 0/8] kernel:lockdep:replace DFS with BFS
    Date

    Hi,
    Currently lockdep uses recursion DFS(depth-first search) algorithm to
    search target in checking lock circle(check_noncircular()),irq-safe
    -> irq-unsafe(check_irq_usage()) and irq inversion when adding a new
    lock dependency. This patches replace the current DFS with BFS, based on
    the following consideration:

    1,no loss of efficiency, no matter DFS or BFS, the running time
    are O(V+E) (V is vertex count, and E is edge count of one
    graph);

    2,BFS may be easily implemented by circular queue and consumes
    much less kernel stack space than DFS for DFS is implemented by
    recursion.

    3, The shortest path can be obtained by BFS if the target is
    found, but can't be got by DFS. By the shortest path, we can
    shorten the lock dependency chain and help to troubleshoot lock
    problem easier than before.




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