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    Subject[PATCH 14/16] drbd: fix schedule in atomic
    Date
    From: Lars Ellenberg <lars.ellenberg@linbit.com>

    An administrative detach used to request a state change directly to D_DISKLESS,
    first suspending IO to avoid the last put_ldev() occuring from an endio handler,
    potentially in irq context.

    This is not enough on the receiving side (typically secondary), we may miss
    some peer_req on the way to local disk, which then may do the last put_ldev()
    from their drbd_peer_request_endio().

    This patch makes the detach always go through the intermediate D_FAILED state.
    We may consider to rename it D_DETACHING.

    Alternative approach would be to create yet an other work item to be scheduled
    on the worker, do the destructor work from there, and get the timing right.

    Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
    Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
    ---
    drivers/block/drbd/drbd_nl.c | 13 +++++++++----
    1 files changed, 9 insertions(+), 4 deletions(-)

    diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
    index 019f762..414503a 100644
    --- a/drivers/block/drbd/drbd_nl.c
    +++ b/drivers/block/drbd/drbd_nl.c
    @@ -1706,12 +1706,17 @@ int drbd_adm_attach(struct sk_buff *skb, struct genl_info *info)
    static int adm_detach(struct drbd_conf *mdev)
    {
    enum drbd_ret_code retcode;
    + int ret;
    drbd_suspend_io(mdev); /* so no-one is stuck in drbd_al_begin_io */
    - retcode = drbd_request_state(mdev, NS(disk, D_DISKLESS));
    - wait_event(mdev->misc_wait,
    - mdev->state.disk != D_DISKLESS ||
    - !atomic_read(&mdev->local_cnt));
    + retcode = drbd_request_state(mdev, NS(disk, D_FAILED));
    + /* D_FAILED will transition to DISKLESS. */
    + ret = wait_event_interruptible(mdev->misc_wait,
    + mdev->state.disk != D_FAILED);
    drbd_resume_io(mdev);
    + if (retcode == SS_IS_DISKLESS)
    + retcode = SS_NOTHING_TO_DO;
    + if (ret)
    + retcode = ERR_INTR;
    return retcode;
    }

    --
    1.7.4.1


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