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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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