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SubjectRe: Bounce buffer deadlock


On Fri, 29 Jun 2001, Steve Lord wrote:

>
> Has anyone else seen a hang like this:
>
> bdflush()
> flush_dirty_buffers()
> ll_rw_block()
> submit_bh(buffer X)
> generic_make_request()
> __make_request()
> create_bounce()
> alloc_bounce_page()
> alloc_page()
> try_to_free_pages()
> do_try_to_free_pages()
> page_launder()
> try_to_free_buffers( , 2) -- i.e. wait for buffers
> sync_page_buffers()
> __wait_on_buffer(buffer X)
>
> Where the buffer head X going in the top of the stack is the same as the one
> we wait on at the bottom.
>
> There still seems to be nothing to prevent the try to free buffers from
> blocking on a buffer like this. Setting a flag on the buffer around the
> create_bounce call, and skipping it in the try_to_free_buffers path would
> be one approach to avoiding this.

Yes there is a bug: Linus is going to put a new fix soon.

> I hit this in 2.4.6-pre6, and I don't see anything in the ac series to protect
> against it.

Thats because the -ac series does not contain the __GFP_BUFFER/__GFP_IO
moditications which are in the -ac series.

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