[PATCH 05/13] block: Hold a reference on zone write plugs to schedule submission

[Damien Le Moal]

Since a zone write plug BIO work is a field of struct blk_zone_wplug, we
must ensure that a zone write plug is never freed when its BIO
submission work is queued or running. Do this by holding a reference on
the zone write plug when the submission work is scheduled for execution
with queue_work() and releasing the reference at the end of the
execution of the work function blk_zone_wplug_bio_work().
The helper function disk_zone_wplug_schedule_bio_work() is introduced to
get a reference on a zone write plug and queue its work. This helper is
used in disk_zone_wplug_unplug_bio() and disk_zone_wplug_handle_error().

Fixes: dd291d77cc90 ("block: Introduce zone write plugging")
Signed-off-by: Damien Le Moal <dlem...@kernel.org>
---
 block/blk-zoned.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 9bded29592e0..03555ea64774 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -1131,6 +1131,19 @@ bool blk_zone_plug_bio(struct bio *bio, unsigned int 
nr_segs)
 }
 EXPORT_SYMBOL_GPL(blk_zone_plug_bio);
 
+static void disk_zone_wplug_schedule_bio_work(struct gendisk *disk,
+                                             struct blk_zone_wplug *zwplug)
+{
+       /*
+        * Take a reference on the zone write plug and schedule the submission
+        * of the next plugged BIO. blk_zone_wplug_bio_work() will release the
+        * reference we take here.
+        */
+       WARN_ON_ONCE(!(zwplug->flags & BLK_ZONE_WPLUG_PLUGGED));
+       atomic_inc(&zwplug->ref);
+       queue_work(disk->zone_wplugs_wq, &zwplug->bio_work);
+}
+
 static void disk_zone_wplug_unplug_bio(struct gendisk *disk,
                                       struct blk_zone_wplug *zwplug)
 {
@@ -1150,8 +1163,8 @@ static void disk_zone_wplug_unplug_bio(struct gendisk 
*disk,
 
        /* Schedule submission of the next plugged BIO if we have one. */
        if (!bio_list_empty(&zwplug->bio_list)) {
+               disk_zone_wplug_schedule_bio_work(disk, zwplug);
                spin_unlock_irqrestore(&zwplug->lock, flags);
-               queue_work(disk->zone_wplugs_wq, &zwplug->bio_work);
                return;
        }
 
@@ -1251,14 +1264,14 @@ static void blk_zone_wplug_bio_work(struct work_struct 
*work)
        if (!bio) {
                zwplug->flags &= ~BLK_ZONE_WPLUG_PLUGGED;
                spin_unlock_irqrestore(&zwplug->lock, flags);
-               return;
+               goto put_zwplug;
        }
 
        if (!blk_zone_wplug_prepare_bio(zwplug, bio)) {
                /* Error recovery will decide what to do with the BIO. */
                bio_list_add_head(&zwplug->bio_list, bio);
                spin_unlock_irqrestore(&zwplug->lock, flags);
-               return;
+               goto put_zwplug;
        }
 
        spin_unlock_irqrestore(&zwplug->lock, flags);
@@ -1274,6 +1287,10 @@ static void blk_zone_wplug_bio_work(struct work_struct 
*work)
         */
        if (bdev->bd_has_submit_bio)
                blk_queue_exit(bdev->bd_disk->queue);
+
+put_zwplug:
+       /* Drop the reference we took in disk_zone_wplug_schedule_bio_work(). */
+       disk_put_zone_wplug(zwplug);
 }
 
 static unsigned int blk_zone_wp_offset(struct blk_zone *zone)
@@ -1353,8 +1370,7 @@ static void disk_zone_wplug_handle_error(struct gendisk 
*disk,
 
        /* Restart BIO submission if we still have any BIO left. */
        if (!bio_list_empty(&zwplug->bio_list)) {
-               WARN_ON_ONCE(!(zwplug->flags & BLK_ZONE_WPLUG_PLUGGED));
-               queue_work(disk->zone_wplugs_wq, &zwplug->bio_work);
+               disk_zone_wplug_schedule_bio_work(disk, zwplug);
                goto unlock;
        }
 
-- 
2.44.0