• Nick Piggin's avatar
    fs: Use rename lock and RCU for multi-step operations · 949854d0
    Nick Piggin authored
    The remaining usages for dcache_lock is to allow atomic, multi-step read-side
    operations over the directory tree by excluding modifications to the tree.
    Also, to walk in the leaf->root direction in the tree where we don't have
    a natural d_lock ordering.
    
    This could be accomplished by taking every d_lock, but this would mean a
    huge number of locks and actually gets very tricky.
    
    Solve this instead by using the rename seqlock for multi-step read-side
    operations, retry in case of a rename so we don't walk up the wrong parent.
    Concurrent dentry insertions are not serialised against.  Concurrent deletes
    are tricky when walking up the directory: our parent might have been deleted
    when dropping locks so also need to check and retry for that.
    
    We can also use the rename lock in cases where livelock is a worry (and it
    is introduced in subsequent patch).
    Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
    949854d0
waitq.c 13.4 KB