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    SubjectRe: [PATCH v2] block: flush queued bios when the process blocks
    On Fri, Oct 09 2015 at  3:52pm -0400,
    Mike Snitzer <snitzer@redhat.com> wrote:

    > Turns out that this change:
    > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=2639638c77768a86216be456c2764e32a2bcd841
    >
    > needed to be reverted with:
    > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=ad3ccd760da7c05b90775372f9b39dc2964086fe
    >
    > Because nested plugs caused generic_make_request()'s onstack bio_list to
    > go out of scope (blk_finish_plug() wouldn't actually flush the list
    > within generic_make_request because XFS already added an outermost
    > plug).
    >
    > But even after fixing that I then hit issues with these changes now
    > resulting in imperfect 'in_generic_make_request' accounting that happens
    > lazily once the outermost plug completes blk_finish_plug. manifested as
    > dm-bufio.c:dm_bufio_prefetch's BUG_ON(dm_bufio_in_request()); hitting.
    >
    > Basically using the blk-core's onstack plugging isn't workable for
    > fixing this deadlock and we're back to having to seriously consider
    > this (with its additional hook in the scheduler):

    http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=a91709cd32b5ca7ca047b68c9299e747f2ae6ca2


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