| Message ID | 20171002225218.18548-7-bart.vanassche@wdc.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
> + /* > + * Do not attempt to freeze the queue of an already quiesced device > + * because that could result in a deadlock. > + */ > + freeze = sdev->sdev_state == SDEV_RUNNING; > + if (freeze) > + blk_mq_freeze_queue(q); > err = scsi_device_set_state(sdev, SDEV_QUIESCE); I don't really like this magic with a freeze inside the lock and the magic dependency on the previous. But I can't really come up with a better idea either.
On Wed, 2017-10-04 at 09:04 +0200, Christoph Hellwig wrote: > > + /* > > + * Do not attempt to freeze the queue of an already quiesced device > > + * because that could result in a deadlock. > > + */ > > + freeze = sdev->sdev_state == SDEV_RUNNING; > > + if (freeze) > > + blk_mq_freeze_queue(q); > > err = scsi_device_set_state(sdev, SDEV_QUIESCE); > > I don't really like this magic with a freeze inside the lock > and the magic dependency on the previous. But I can't really come up > with a better idea either. The deadlock I referred to in my comment can only occur if any code would change the SCSI device state into SDEV_QUIESCE without freezing the request queue first. I will look into freezing the queue without holding the sdev state mutex. Bart.
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 62f905b22821..e0bef5c9dd14 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -2927,21 +2927,25 @@ static void scsi_wait_for_queuecommand(struct scsi_device *sdev) int scsi_device_quiesce(struct scsi_device *sdev) { + struct request_queue *q = sdev->request_queue; + bool freeze; int err; mutex_lock(&sdev->state_mutex); + /* + * Do not attempt to freeze the queue of an already quiesced device + * because that could result in a deadlock. + */ + freeze = sdev->sdev_state == SDEV_RUNNING; + if (freeze) + blk_mq_freeze_queue(q); err = scsi_device_set_state(sdev, SDEV_QUIESCE); mutex_unlock(&sdev->state_mutex); - if (err) - return err; + if (freeze) + blk_mq_unfreeze_queue(q); - scsi_run_queue(sdev->request_queue); - while (atomic_read(&sdev->device_busy)) { - msleep_interruptible(200); - scsi_run_queue(sdev->request_queue); - } - return 0; + return err; } EXPORT_SYMBOL(scsi_device_quiesce);
Avoid that it can take 200 ms too long to wait for requests to finish. Note: blk_mq_freeze_queue() uses a wait queue to wait for ongoing requests to finish. Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com> Cc: Martin K. Petersen <martin.petersen@oracle.com> Cc: Ming Lei <ming.lei@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Hannes Reinecke <hare@suse.com> Cc: Johannes Thumshirn <jthumshirn@suse.de> --- drivers/scsi/scsi_lib.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-)