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    SubjectRe: [PATCH 1/2] scsi: sas: flush destruct workqueue on device unregister
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    On 29/03/2017 12:29, Johannes Thumshirn wrote:
    > On Wed, Mar 29, 2017 at 12:15:44PM +0100, John Garry wrote:
    >> On 29/03/2017 10:41, Johannes Thumshirn wrote:
    >>> In the advent of an SAS device unregister we have to wait for all destruct
    >>> works to be done to not accidently delay deletion of a SAS rphy or it's
    >>> children to the point when we're removing the SCSI or SAS hosts.
    >>>
    >>> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
    >>> ---
    >>> drivers/scsi/libsas/sas_discover.c | 4 ++++
    >>> 1 file changed, 4 insertions(+)
    >>>
    >>> diff --git a/drivers/scsi/libsas/sas_discover.c b/drivers/scsi/libsas/sas_discover.c
    >>> index 60de662..75b18f1 100644
    >>> --- a/drivers/scsi/libsas/sas_discover.c
    >>> +++ b/drivers/scsi/libsas/sas_discover.c
    >>> @@ -382,9 +382,13 @@ void sas_unregister_dev(struct asd_sas_port *port, struct domain_device *dev)
    >>> }
    >>>
    >>> if (!test_and_set_bit(SAS_DEV_DESTROY, &dev->state)) {
    >>> + struct sas_discovery *disc = &dev->port->disc;
    >>> + struct sas_work *sw = &disc->disc_work[DISCE_DESTRUCT].work;
    >>> +
    >>> sas_rphy_unlink(dev->rphy);
    >>> list_move_tail(&dev->disco_list_node, &port->destroy_list);
    >>> sas_discover_event(dev->port, DISCE_DESTRUCT);
    >>> + flush_work(&sw->work);
    >>
    >> I quickly tested plugging out the expander and we never get past this call
    >> to flush - a hang results:
    >
    > Can you activat lockdep so we can see which lock it is that we're blocking on?
    >

    I have it on:
    CONFIG_LOCKDEP_SUPPORT=y
    CONFIG_LOCKD=y
    CONFIG_LOCKD_V4=y

    > It's most likely in sas_unregister_common_dev() but this function takes two spin
    > locks, port->dev_list_lock and ha->lock.
    >

    We can see from the callstack I provided that we're working in workqueue
    scsi_wq_0 and trying to flush that same queue.

    Much appreciated,
    John

    > Thanks a lot,
    > Johannes
    >


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