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    SubjectRe: Bounce buffer deadlock

    On Sat, 30 Jun 2001, Steve Lord wrote:
    > It looks to me as if all memory allocations of type GFP_BUFFER which happen
    > in generic_make_request downwards can hit the same type of deadlock, so
    > bounce buffers, the request functions of the raid and lvm paths can all
    > end up in try_to_free_buffers on a buffer they themselves hold the lock on.

    .. which is why GFP_BUFFER doesn't exist any more in the most recent
    pre-kernels (oops, this is pre8 only, not pre7 like I said in the previous

    The problem is that GFP_BUFFER used to mean two things: "don't call
    low-level filesystem" and "don't do IO". Some of the pre-kernels starting
    to make it mean "don't call low-level FS" only. The later ones split up
    the semantics, so that the cases which care about FS deadlocks use
    "GFP_NOFS", and the cases that care about IO recursion use "GFP_NOIO", so
    that we don't overload the meaning of GFP_BUFFER.

    That allows us to do the best we can - still flushing out dirty buffers
    when that's ok (like when a filesystem wants more memory), and giving the
    allocator better control over exactly _what_ he objects to.


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