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Date: Mon, 5 Oct 2015 16:13:27 +0200
From: Roger Pau Monné <roger.pau@...rix.com>
To: Bob Liu <bob.liu@...cle.com>, <xen-devel@...ts.xen.org>
CC: <david.vrabel@...rix.com>, <linux-kernel@...r.kernel.org>,
<konrad.wilk@...cle.com>, <felipe.franciosi@...rix.com>,
<axboe@...com>, <hch@...radead.org>, <avanzini.arianna@...il.com>,
<rafal.mielniczuk@...rix.com>, <boris.ostrovsky@...cle.com>,
<jonathan.davies@...rix.com>
Subject: Re: [PATCH v3 5/9] xen/blkfront: convert per device io_lock to per
ring ring_lock
El 05/09/15 a les 14.39, Bob Liu ha escrit:
> The per device io_lock became a coarser grained lock after multi-queues/rings
> was introduced, this patch converts it to a fine-grained per ring lock.
>
> NOTE: The per dev_info structure was no more protected by any lock.
I would rewrite this as:
Note that the per-device blkfront_dev_info structure is no longer
protected by any lock.
>
> Signed-off-by: Bob Liu <bob.liu@...cle.com>
> ---
> drivers/block/xen-blkfront.c | 44 +++++++++++++++++++-----------------------
> 1 file changed, 20 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index bf45c99..1cae76b 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -123,6 +123,7 @@ MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the
> struct blkfront_ring_info
> {
> struct blkif_front_ring ring;
> + spinlock_t ring_lock;
> unsigned int ring_ref[XENBUS_MAX_RING_PAGES];
> unsigned int evtchn, irq;
> struct work_struct work;
> @@ -141,7 +142,6 @@ struct blkfront_ring_info
> * putting all kinds of interesting stuff here :-)
> */
> struct blkfront_dev_info {
> - spinlock_t io_lock;
> struct mutex mutex;
> struct xenbus_device *xbdev;
> struct gendisk *gd;
> @@ -637,29 +637,28 @@ static int blkif_queue_rq(struct blk_mq_hw_ctx *hctx,
> const struct blk_mq_queue_data *qd)
> {
> struct blkfront_ring_info *rinfo = (struct blkfront_ring_info *)hctx->driver_data;
> - struct blkfront_dev_info *dinfo = rinfo->dinfo;
>
> blk_mq_start_request(qd->rq);
> - spin_lock_irq(&dinfo->io_lock);
> + spin_lock_irq(&rinfo->ring_lock);
> if (RING_FULL(&rinfo->ring))
> goto out_busy;
>
> - if (blkif_request_flush_invalid(qd->rq, dinfo))
> + if (blkif_request_flush_invalid(qd->rq, rinfo->dinfo))
> goto out_err;
>
> if (blkif_queue_request(qd->rq, rinfo))
> goto out_busy;
>
> flush_requests(rinfo);
> - spin_unlock_irq(&dinfo->io_lock);
> + spin_unlock_irq(&rinfo->ring_lock);
> return BLK_MQ_RQ_QUEUE_OK;
>
> out_err:
> - spin_unlock_irq(&dinfo->io_lock);
> + spin_unlock_irq(&rinfo->ring_lock);
> return BLK_MQ_RQ_QUEUE_ERROR;
>
> out_busy:
> - spin_unlock_irq(&dinfo->io_lock);
> + spin_unlock_irq(&rinfo->ring_lock);
> blk_mq_stop_hw_queue(hctx);
> return BLK_MQ_RQ_QUEUE_BUSY;
> }
> @@ -961,7 +960,7 @@ static void xlvbd_release_gendisk(struct blkfront_dev_info *dinfo)
> dinfo->gd = NULL;
> }
>
> -/* Must be called with io_lock holded */
> +/* Must be called with ring_lock holded */
^ held.
> static void kick_pending_request_queues(struct blkfront_ring_info *rinfo)
> {
> if (!RING_FULL(&rinfo->ring))
> @@ -972,10 +971,10 @@ static void blkif_restart_queue(struct work_struct *work)
> {
> struct blkfront_ring_info *rinfo = container_of(work, struct blkfront_ring_info, work);
>
> - spin_lock_irq(&rinfo->dinfo->io_lock);
> + spin_lock_irq(&rinfo->ring_lock);
> if (rinfo->dinfo->connected == BLKIF_STATE_CONNECTED)
> kick_pending_request_queues(rinfo);
This seems wrong, why are you acquiring a per-ring lock in order to
check a per-device field? IMHO, I think you need to introduce a
per-device lock or drop the locking around this chunk if it's really not
needed.
> - spin_unlock_irq(&rinfo->dinfo->io_lock);
> + spin_unlock_irq(&rinfo->ring_lock);
> }
>
> static void blkif_free(struct blkfront_dev_info *dinfo, int suspend)
> @@ -986,7 +985,6 @@ static void blkif_free(struct blkfront_dev_info *dinfo, int suspend)
> struct blkfront_ring_info *rinfo;
>
> /* Prevent new requests being issued until we fix things up. */
> - spin_lock_irq(&dinfo->io_lock);
> dinfo->connected = suspend ?
> BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
> /* No more blkif_request(). */
> @@ -996,6 +994,7 @@ static void blkif_free(struct blkfront_dev_info *dinfo, int suspend)
> for (r_index = 0; r_index < dinfo->nr_rings; r_index++) {
> rinfo = &dinfo->rinfo[r_index];
>
> + spin_lock_irq(&rinfo->ring_lock);
> /* Remove all persistent grants */
> if (!list_empty(&rinfo->grants)) {
> list_for_each_entry_safe(persistent_gnt, n,
> @@ -1071,7 +1070,7 @@ free_shadow:
>
> /* No more gnttab callback work. */
> gnttab_cancel_free_callback(&rinfo->callback);
> - spin_unlock_irq(&dinfo->io_lock);
> + spin_unlock_irq(&rinfo->ring_lock);
>
> /* Flush gnttab callback work. Must be done with no locks held. */
> flush_work(&rinfo->work);
> @@ -1180,13 +1179,10 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
> struct blkfront_ring_info *rinfo = (struct blkfront_ring_info *)dev_id;
> struct blkfront_dev_info *dinfo = rinfo->dinfo;
>
> - spin_lock_irqsave(&dinfo->io_lock, flags);
> -
> - if (unlikely(dinfo->connected != BLKIF_STATE_CONNECTED)) {
> - spin_unlock_irqrestore(&dinfo->io_lock, flags);
> + if (unlikely(dinfo->connected != BLKIF_STATE_CONNECTED))
> return IRQ_HANDLED;
> - }
>
> + spin_lock_irqsave(&rinfo->ring_lock, flags);
> again:
> rp = rinfo->ring.sring->rsp_prod;
> rmb(); /* Ensure we see queued responses up to 'rp'. */
> @@ -1279,7 +1275,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>
> kick_pending_request_queues(rinfo);
>
> - spin_unlock_irqrestore(&dinfo->io_lock, flags);
> + spin_unlock_irqrestore(&rinfo->ring_lock, flags);
>
> return IRQ_HANDLED;
> }
> @@ -1534,7 +1530,6 @@ static int blkfront_probe(struct xenbus_device *dev,
> }
>
> mutex_init(&dinfo->mutex);
> - spin_lock_init(&dinfo->io_lock);
> dinfo->xbdev = dev;
> dinfo->vdevice = vdevice;
> dinfo->connected = BLKIF_STATE_DISCONNECTED;
> @@ -1550,6 +1545,7 @@ static int blkfront_probe(struct xenbus_device *dev,
> for (r_index = 0; r_index < dinfo->nr_rings; r_index++) {
> rinfo = &dinfo->rinfo[r_index];
>
> + spin_lock_init(&rinfo->ring_lock);
> INIT_LIST_HEAD(&rinfo->grants);
> INIT_LIST_HEAD(&rinfo->indirect_pages);
> rinfo->persistent_gnts_c = 0;
> @@ -1650,16 +1646,16 @@ static int blkif_recover(struct blkfront_dev_info *dinfo)
>
> xenbus_switch_state(dinfo->xbdev, XenbusStateConnected);
>
> - spin_lock_irq(&dinfo->io_lock);
> -
> /* Now safe for us to use the shared ring */
> dinfo->connected = BLKIF_STATE_CONNECTED;
>
> for (r_index = 0; r_index < dinfo->nr_rings; r_index++) {
> rinfo = &dinfo->rinfo[r_index];
>
> + spin_lock_irq(&rinfo->ring_lock);
> /* Kick any other new requests queued since we resumed */
> kick_pending_request_queues(rinfo);
> + spin_unlock_irq(&rinfo->ring_lock);
> }
>
> list_for_each_entry_safe(req, n, &requests, queuelist) {
> @@ -1668,7 +1664,6 @@ static int blkif_recover(struct blkfront_dev_info *dinfo)
> BUG_ON(req->nr_phys_segments > segs);
> blk_mq_requeue_request(req);
> }
> - spin_unlock_irq(&dinfo->io_lock);
> blk_mq_kick_requeue_list(dinfo->rq);
>
> while ((bio = bio_list_pop(&bio_list)) != NULL) {
> @@ -2049,13 +2044,14 @@ static void blkfront_connect(struct blkfront_dev_info *dinfo)
> xenbus_switch_state(dinfo->xbdev, XenbusStateConnected);
>
> /* Kick pending requests. */
> - spin_lock_irq(&dinfo->io_lock);
> dinfo->connected = BLKIF_STATE_CONNECTED;
> for (i = 0; i < dinfo->nr_rings; i++) {
> rinfo = &dinfo->rinfo[i];
> +
> + spin_lock_irq(&rinfo->ring_lock);
> kick_pending_request_queues(rinfo);
> + spin_unlock_irq(&rinfo->ring_lock);
> }
> - spin_unlock_irq(&dinfo->io_lock);
>
> add_disk(dinfo->gd);
>
>
--
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