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    SubjectRe: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty()
    On Wed, Sep 12, 2012 at 05:00:48PM +0900, OGAWA Hirofumi wrote:
    > Fengguang Wu <fengguang.wu@intel.com> writes:
    >
    > > On Wed, Sep 12, 2012 at 03:28:42AM +0900, OGAWA Hirofumi wrote:
    > >>
    > >> If bdi has BDI_CAP_NO_WRITEBACK, bdi_forker_thread() doesn't start
    > >> writeback thread. This means there is no consumer of work item made
    > >> by bdi_queue_work().
    > >>
    > >> This adds to checking of !bdi_cap_writeback_dirty(sb->s_bdi) before
    > >> calling bdi_queue_work(), otherwise queued work never be consumed.
    > >
    > > Thanks for catching this! Does this bug have any side effects other
    > > than memory leaking?
    > >
    > > It may be possible for some caller that actually expect it to do some
    > > work to make progress, otherwise will eventually block. If so, we'll
    > > need to fix the caller.
    >
    > If used custom bdi with BDI_CAP_NO_WRITEBACK, wait_for_completion()
    > (e.g. sync_inodes_sb()) will be blocked forever.

    The sync(2) block cannot be fixed by this patch?

    > I tested by custom bdi with BDI_CAP_NO_WRITEBACK - sync(2) blocked
    > forever by this reason.

    What's your test script? How do you create/use that custom bdi?

    Thanks,
    Fengguang


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