On 4/2/19 8:41 PM, Ming Lei wrote:
On Wed, Apr 3, 2019 at 12:03 AM Bart Van Assche <bvanassche@xxxxxxx> wrote:
On Tue, 2019-04-02 at 19:48 +0800, Ming Lei wrote:
scsi_device's refcount is always grabed in IO path.
^^^^^^
grabbed?
Turns out it isn't necessary, becasue blk_queue_cleanup() will
drain any in-flight IOs, then cancel timeout/requeue work, and
SCSI's requeue_work is canceled too in __scsi_remove_device().
Also scsi_device won't go away until blk_cleanup_queue() is done.
So don't hold the refcount in IO path.
Holding the device reference count was definitely necessary in the past.
You may want to reflect this in the patch description by mentioning that
grabbing that reference count is no longer required today because the
draining mechanism now waits for requeuing to occur. I don't think that
was the case for the legacy block layer.
You must forget we have switched to blk_queue_enter() for legacy block
layer for a while, :-)
I definitely haven't forgotten that. I was referring to the time before
blk_queue_enter() / blk_queue_exit() was introduced in the legacy block
layer.
Bart.
