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[dm-devel] block: Deprecate QUEUE_FLAG_CLUSTER and use queue_limits instead



When stacking devices a request_queue is not always available. This
forced us to have a no_cluster flag in the queue_limits that could be
used as a carrier until the request_queue had been set up for a
metadevice.

There were several problems with that approach. First of all it was up
to the stacking device to remember to set queue flag after stacking had
completed. Also, the queue flag and the queue limits had to be kept in
sync at all times. We got that wrong, which could lead to us issuing
commands that went beyond the max scatterlist limit set by the driver.

The proper fix is to avoid having two flags for tracking the same thing.
We deprecate QUEUE_FLAG_CLUSTER and use the queue limit directly in the
block layer merging functions. The queue_limit 'no_cluster' is turned
into 'cluster' to avoid double negatives and to ease stacking.
Clustering defaults to being enabled as before. The queue flag logic is
removed from the stacking function, and explicitly setting the cluster
flag is no longer necessary in DM and MD.

Reported-by: Ed Lin <ed lin promise com>
Signed-off-by: Martin K. Petersen <martin petersen oracle com>

---

 block/blk-merge.c       |    6 +++---
 block/blk-settings.c    |   25 ++-----------------------
 block/blk-sysfs.c       |    2 +-
 drivers/md/dm-table.c   |    5 -----
 drivers/md/md.c         |    3 ---
 drivers/scsi/scsi_lib.c |    2 +-
 include/linux/blkdev.h  |    9 ++++++---
 7 files changed, 13 insertions(+), 39 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 77b7c26..11b9952 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -21,7 +21,7 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
 		return 0;
 
 	fbio = bio;
-	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
+	cluster = blk_queue_cluster(q);
 	seg_size = 0;
 	nr_phys_segs = 0;
 	for_each_bio(bio) {
@@ -87,7 +87,7 @@ EXPORT_SYMBOL(blk_recount_segments);
 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 				   struct bio *nxt)
 {
-	if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
+	if (blk_queue_cluster(q))
 		return 0;
 
 	if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
@@ -123,7 +123,7 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 	int nsegs, cluster;
 
 	nsegs = 0;
-	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
+	cluster = blk_queue_cluster(q);
 
 	/*
 	 * for each bio in rq
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 701859f..e55f5fc 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -126,7 +126,7 @@ void blk_set_default_limits(struct queue_limits *lim)
 	lim->alignment_offset = 0;
 	lim->io_opt = 0;
 	lim->misaligned = 0;
-	lim->no_cluster = 0;
+	lim->cluster = 1;
 }
 EXPORT_SYMBOL(blk_set_default_limits);
 
@@ -464,15 +464,6 @@ EXPORT_SYMBOL(blk_queue_io_opt);
 void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
 {
 	blk_stack_limits(&t->limits, &b->limits, 0);
-
-	if (!t->queue_lock)
-		WARN_ON_ONCE(1);
-	else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
-		unsigned long flags;
-		spin_lock_irqsave(t->queue_lock, flags);
-		queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
-		spin_unlock_irqrestore(t->queue_lock, flags);
-	}
 }
 EXPORT_SYMBOL(blk_queue_stack_limits);
 
@@ -545,7 +536,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 	t->io_min = max(t->io_min, b->io_min);
 	t->io_opt = lcm(t->io_opt, b->io_opt);
 
-	t->no_cluster |= b->no_cluster;
+	t->cluster &= b->cluster;
 	t->discard_zeroes_data &= b->discard_zeroes_data;
 
 	/* Physical block size a multiple of the logical block size? */
@@ -641,7 +632,6 @@ void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
 		       sector_t offset)
 {
 	struct request_queue *t = disk->queue;
-	struct request_queue *b = bdev_get_queue(bdev);
 
 	if (bdev_stack_limits(&t->limits, bdev, offset >> 9) < 0) {
 		char top[BDEVNAME_SIZE], bottom[BDEVNAME_SIZE];
@@ -652,17 +642,6 @@ void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
 		printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
 		       top, bottom);
 	}
-
-	if (!t->queue_lock)
-		WARN_ON_ONCE(1);
-	else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
-		unsigned long flags;
-
-		spin_lock_irqsave(t->queue_lock, flags);
-		if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
-			queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
-		spin_unlock_irqrestore(t->queue_lock, flags);
-	}
 }
 EXPORT_SYMBOL(disk_stack_limits);
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 013457f..41fb691 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -119,7 +119,7 @@ static ssize_t queue_max_integrity_segments_show(struct request_queue *q, char *
 
 static ssize_t queue_max_segment_size_show(struct request_queue *q, char *page)
 {
-	if (test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
+	if (blk_queue_cluster(q))
 		return queue_var_show(queue_max_segment_size(q), (page));
 
 	return queue_var_show(PAGE_CACHE_SIZE, (page));
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 90267f8..e2da191 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1131,11 +1131,6 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 	 */
 	q->limits = *limits;
 
-	if (limits->no_cluster)
-		queue_flag_clear_unlocked(QUEUE_FLAG_CLUSTER, q);
-	else
-		queue_flag_set_unlocked(QUEUE_FLAG_CLUSTER, q);
-
 	if (!dm_table_supports_discards(t))
 		queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, q);
 	else
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 84c46a1..52694d2 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4296,9 +4296,6 @@ static int md_alloc(dev_t dev, char *name)
 		goto abort;
 	mddev->queue->queuedata = mddev;
 
-	/* Can be unlocked because the queue is new: no concurrency */
-	queue_flag_set_unlocked(QUEUE_FLAG_CLUSTER, mddev->queue);
-
 	blk_queue_make_request(mddev->queue, md_make_request);
 
 	disk = alloc_disk(1 << shift);
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index b55b0ec..493f599 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1645,7 +1645,7 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
 
 	/* New queue, no concurrency on queue_flags */
 	if (!shost->use_clustering)
-		queue_flag_clear_unlocked(QUEUE_FLAG_CLUSTER, q);
+		q->limits.cluster = 0;
 
 	/*
 	 * set a reasonable default alignment on word boundaries: the
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index aae86fd..95aeeeb 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -250,7 +250,7 @@ struct queue_limits {
 
 	unsigned char		misaligned;
 	unsigned char		discard_misaligned;
-	unsigned char		no_cluster;
+	unsigned char		cluster;
 	signed char		discard_zeroes_data;
 };
 
@@ -380,7 +380,6 @@ struct request_queue
 #endif
 };
 
-#define QUEUE_FLAG_CLUSTER	0	/* cluster several segments into 1 */
 #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */
 #define QUEUE_FLAG_STOPPED	2	/* queue is stopped */
 #define	QUEUE_FLAG_SYNCFULL	3	/* read queue has been filled */
@@ -403,7 +402,6 @@ struct request_queue
 #define QUEUE_FLAG_SECDISCARD  19	/* supports SECDISCARD */
 
 #define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
-				 (1 << QUEUE_FLAG_CLUSTER) |		\
 				 (1 << QUEUE_FLAG_STACKABLE)	|	\
 				 (1 << QUEUE_FLAG_SAME_COMP)	|	\
 				 (1 << QUEUE_FLAG_ADD_RANDOM))
@@ -510,6 +508,11 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
 
 #define rq_data_dir(rq)		((rq)->cmd_flags & 1)
 
+static inline unsigned int blk_queue_cluster(struct request_queue *q)
+{
+	return q->limits.cluster;
+}
+
 /*
  * We regard a request as sync, if either a read or a sync write
  */


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