[PATCH v2 2/5] xen/blkfront: cleanup stale persistent grants

Juergen Gross
2018-08-08T14:25:25Z

Add a periodic cleanup function to remove old persistent grants which
are no longer in use on the backend side. This avoids starvation in
case there are lots of persistent grants for a device which no longer
is involved in I/O business.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
drivers/block/xen-blkfront.c | 94 ++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 90 insertions(+), 4 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index b5cedccb5d7d..7c4b1b9d3971 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -46,6 +46,7 @@
#include <linux/scatterlist.h>
#include <linux/bitmap.h>
#include <linux/list.h>
+#include <linux/workqueue.h>

#include <xen/xen.h>
#include <xen/xenbus.h>
@@ -121,6 +122,8 @@ static inline struct blkif_req *blkif_req(struct request *rq)

static DEFINE_MUTEX(blkfront_mutex);
static const struct block_device_operations xlvbd_block_fops;
+static struct delayed_work blkfront_work;
+static LIST_HEAD(info_list);

/*
* Maximum number of segments in indirect requests, the actual value used by
@@ -216,6 +219,7 @@ struct blkfront_info
/* Save uncomplete reqs and bios for migration. */
struct list_head requests;
struct bio_list bio_list;
+ struct list_head info_list;
};

static unsigned int nr_minors;
@@ -1764,6 +1768,12 @@ static int write_per_ring_nodes(struct xenbus_transaction xbt,
return err;
}

+static void free_info(struct blkfront_info *info)
+{
+ list_del(&info->info_list);
+ kfree(info);
+}
+
/* Common code used when first setting up, and when resuming. */
static int talk_to_blkback(struct xenbus_device *dev,
struct blkfront_info *info)
@@ -1885,7 +1895,10 @@ static int talk_to_blkback(struct xenbus_device *dev,
destroy_blkring:
blkif_free(info, 0);

- kfree(info);
+ mutex_lock(&blkfront_mutex);
+ free_info(info);
+ mutex_unlock(&blkfront_mutex);
+
dev_set_drvdata(&dev->dev, NULL);

return err;
@@ -1996,6 +2009,10 @@ static int blkfront_probe(struct xenbus_device *dev,
info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
dev_set_drvdata(&dev->dev, info);

+ mutex_lock(&blkfront_mutex);
+ list_add(&info->info_list, &info_list);
+ mutex_unlock(&blkfront_mutex);
+
return 0;
}

@@ -2306,6 +2323,12 @@ static void blkfront_gather_backend_features(struct blkfront_info *info)
if (indirect_segments <= BLKIF_MAX_SEGMENTS_PER_REQUEST)
indirect_segments = 0;
info->max_indirect_segments = indirect_segments;
+
+ if (info->feature_persistent) {
+ mutex_lock(&blkfront_mutex);
+ schedule_delayed_work(&blkfront_work, HZ * 10);
+ mutex_unlock(&blkfront_mutex);
+ }
}

/*
@@ -2487,7 +2510,9 @@ static int blkfront_remove(struct xenbus_device *xbdev)
mutex_unlock(&info->mutex);

if (!bdev) {
- kfree(info);
+ mutex_lock(&blkfront_mutex);
+ free_info(info);
+ mutex_unlock(&blkfront_mutex);
return 0;
}

@@ -2507,7 +2532,9 @@ static int blkfront_remove(struct xenbus_device *xbdev)
if (info && !bdev->bd_openers) {
xlvbd_release_gendisk(info);
disk->private_data = NULL;
- kfree(info);
+ mutex_lock(&blkfront_mutex);
+ free_info(info);
+ mutex_unlock(&blkfront_mutex);
}

mutex_unlock(&bdev->bd_mutex);
@@ -2590,7 +2617,7 @@ static void blkif_release(struct gendisk *disk, fmode_t mode)
dev_info(disk_to_dev(bdev->bd_disk), "releasing disk\n");
xlvbd_release_gendisk(info);
disk->private_data = NULL;
- kfree(info);
+ free_info(info);
}

out:
@@ -2623,6 +2650,61 @@ static struct xenbus_driver blkfront_driver = {
.is_ready = blkfront_is_ready,
};

+static void purge_persistent_grants(struct blkfront_info *info)
+{
+ unsigned int i;
+ unsigned long flags;
+
+ for (i = 0; i < info->nr_rings; i++) {
+ struct blkfront_ring_info *rinfo = &info->rinfo[i];
+ struct grant *gnt_list_entry, *tmp;
+
+ spin_lock_irqsave(&rinfo->ring_lock, flags);
+
+ if (rinfo->persistent_gnts_c == 0) {
+ spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+ continue;
+ }
+
+ list_for_each_entry_safe(gnt_list_entry, tmp, &rinfo->grants,
+ node) {
+ if (gnt_list_entry->gref == GRANT_INVALID_REF ||
+ gnttab_query_foreign_access(gnt_list_entry->gref))
+ continue;
+
+ list_del(&gnt_list_entry->node);
+ gnttab_end_foreign_access(gnt_list_entry->gref, 0, 0UL);
+ rinfo->persistent_gnts_c--;
+ __free_page(gnt_list_entry->page);
+ kfree(gnt_list_entry);
+ }
+
+ spin_unlock_irqrestore(&rinfo->ring_lock, flags);
+ }
+}
+
+static void blkfront_delay_work(struct work_struct *work)
+{
+ struct blkfront_info *info;
+ bool need_schedule_work = false;
+
+ mutex_lock(&blkfront_mutex);
+
+ list_for_each_entry(info, &info_list, info_list) {
+ if (info->feature_persistent) {
+ need_schedule_work = true;
+ mutex_lock(&info->mutex);
+ purge_persistent_grants(info);
+ mutex_unlock(&info->mutex);
+ }
+ }
+
+ if (need_schedule_work)
+ schedule_delayed_work(&blkfront_work, HZ * 10);
+
+ mutex_unlock(&blkfront_mutex);
+}
+
static int __init xlblk_init(void)
{
int ret;
@@ -2655,6 +2737,8 @@ static int __init xlblk_init(void)
return -ENODEV;
}

+ INIT_DELAYED_WORK(&blkfront_work, blkfront_delay_work);
+
ret = xenbus_register_frontend(&blkfront_driver);
if (ret) {
unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
@@ -2668,6 +2752,8 @@ module_init(xlblk_init);

static void __exit xlblk_exit(void)
{
+ cancel_delayed_work_sync(&blkfront_work);
+
xenbus_unregister_driver(&blkfront_driver);
unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
kfree(minors);
--
2.13.7