block: Use a zone write plug BIO work for REQ_NOWAIT BIOs

For zoned block devices, a write BIO issued to a zone that has no
on-going writes will be prepared for execution and allowed to execute
immediately by blk_zone_wplug_handle_write() (called from
blk_zone_plug_bio()). However, if this BIO specifies REQ_NOWAIT, the
allocation of a request for its execution in blk_mq_submit_bio() may
fail after blk_zone_plug_bio() completed, marking the target zone of the
BIO as plugged. When this BIO is retried later on, it will be blocked as
the zone write plug of the target zone is in a plugged state without any
on-going write operation (completion of write operations trigger
unplugging of the next write BIOs for a zone). This leads to a BIO that
is stuck in a zone write plug and never completes, which results in
various issues such as hung tasks.

Avoid this problem by always executing REQ_NOWAIT write BIOs using the
BIO work of a zone write plug. This ensure that we never block the BIO
issuer and can thus safely ignore the REQ_NOWAIT flag when executing the
BIO from the zone write plug BIO work.

Since such BIO may be the first write BIO issued to a zone with no
on-going write, modify disk_zone_wplug_add_bio() to schedule the zone
write plug BIO work if the write plug is not already marked with the
BLK_ZONE_WPLUG_PLUGGED flag. This scheduling is otherwise not necessary
as the completion of the on-going write for the zone will schedule the
execution of the next plugged BIOs.

blk_zone_wplug_handle_write() is also fixed to better handle zone write
plug allocation failures for REQ_NOWAIT BIOs by failing a write BIO
using bio_wouldblock_error() instead of bio_io_error().

Reported-by: Bart Van Assche <[email protected]>
Fixes: dd291d7 ("block: Introduce zone write plugging")
Cc: [email protected]
Signed-off-by: Damien Le Moal <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Martin K. Petersen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: damien-lemoal

block/blk-zoned.c

@@ -746,9 +746,25 @@ static bool blk_zone_wplug_handle_reset_all(struct bio *bio)
 	return false;
 }
 
-static inline void blk_zone_wplug_add_bio(struct blk_zone_wplug *zwplug,
-					  struct bio *bio, unsigned int nr_segs)
+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));
+	refcount_inc(&zwplug->ref);
+	queue_work(disk->zone_wplugs_wq, &zwplug->bio_work);
+}
+
+static inline void disk_zone_wplug_add_bio(struct gendisk *disk,
+				struct blk_zone_wplug *zwplug,
+				struct bio *bio, unsigned int nr_segs)
 {
+	bool schedule_bio_work = false;
+
 	/*
 	 * Grab an extra reference on the BIO request queue usage counter.
 	 * This reference will be reused to submit a request for the BIO for
@@ -764,6 +780,16 @@ static inline void blk_zone_wplug_add_bio(struct blk_zone_wplug *zwplug,
 	 */
 	bio_clear_polled(bio);
 
+	/*
+	 * REQ_NOWAIT BIOs are always handled using the zone write plug BIO
+	 * work, which can block. So clear the REQ_NOWAIT flag and schedule the
+	 * work if this is the first BIO we are plugging.
+	 */
+	if (bio->bi_opf & REQ_NOWAIT) {
+		schedule_bio_work = !(zwplug->flags & BLK_ZONE_WPLUG_PLUGGED);
+		bio->bi_opf &= ~REQ_NOWAIT;
+	}
+
 	/*
 	 * Reuse the poll cookie field to store the number of segments when
 	 * split to the hardware limits.
@@ -777,6 +803,11 @@ static inline void blk_zone_wplug_add_bio(struct blk_zone_wplug *zwplug,
 	 * at the tail of the list to preserve the sequential write order.
 	 */
 	bio_list_add(&zwplug->bio_list, bio);
+
+	zwplug->flags |= BLK_ZONE_WPLUG_PLUGGED;
+
+	if (schedule_bio_work)
+		disk_zone_wplug_schedule_bio_work(disk, zwplug);
 }
 
 /*
@@ -970,7 +1001,10 @@ static bool blk_zone_wplug_handle_write(struct bio *bio, unsigned int nr_segs)
 
 	zwplug = disk_get_and_lock_zone_wplug(disk, sector, gfp_mask, &flags);
 	if (!zwplug) {
-		bio_io_error(bio);
+		if (bio->bi_opf & REQ_NOWAIT)
+			bio_wouldblock_error(bio);
+		else
+			bio_io_error(bio);
 		return true;
 	}
 
@@ -979,9 +1013,11 @@ static bool blk_zone_wplug_handle_write(struct bio *bio, unsigned int nr_segs)
 
 	/*
 	 * If the zone is already plugged or has a pending error, add the BIO
-	 * to the plug BIO list. Otherwise, plug and let the BIO execute.
+	 * to the plug BIO list. Do the same for REQ_NOWAIT BIOs to ensure that
+	 * we will not see a BLK_STS_AGAIN failure if we let the BIO execute.
+	 * Otherwise, plug and let the BIO execute.
 	 */
-	if (zwplug->flags & BLK_ZONE_WPLUG_BUSY)
+	if (zwplug->flags & BLK_ZONE_WPLUG_BUSY || (bio->bi_opf & REQ_NOWAIT))
 		goto plug;
 
 	/*
@@ -998,8 +1034,7 @@ static bool blk_zone_wplug_handle_write(struct bio *bio, unsigned int nr_segs)
 	return false;
 
 plug:
-	zwplug->flags |= BLK_ZONE_WPLUG_PLUGGED;
-	blk_zone_wplug_add_bio(zwplug, bio, nr_segs);
+	disk_zone_wplug_add_bio(disk, zwplug, bio, nr_segs);
 
 	spin_unlock_irqrestore(&zwplug->lock, flags);
 
@@ -1083,19 +1118,6 @@ 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));
-	refcount_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)
 {