Date: Mon, 9 Oct 2006 03:03:32 -0400
From: Jeff Garzik <jgarzik@redhat.com>
Subject: [RHEL5 PATCH 1/2] block & scsi: fix shared tag maps


Update shared TCQ map support, which was always fundamentally incomplete
and broken.  From upstream.

The only publicly visible change is an added struct member to Scsi_Host.

Required for patch #2, which addresses BZ#209179.


 block/ll_rw_blk.c        |  122 +++++++++++++++++++++++++++++++++++++----------
 drivers/scsi/hosts.c     |    3 +
 include/linux/blkdev.h   |    2 
 include/scsi/scsi_host.h |    7 ++
 include/scsi/scsi_tcq.h  |   15 +++++
 5 files changed, 123 insertions(+), 26 deletions(-)

diff -urN linux-2.6.18.x86_64/block/ll_rw_blk.c linux-2.6.18.x86_64.stex1/block/ll_rw_blk.c
--- linux-2.6.18.x86_64/block/ll_rw_blk.c	2006-09-19 23:42:06.000000000 -0400
+++ linux-2.6.18.x86_64.stex1/block/ll_rw_blk.c	2006-10-08 21:28:47.000000000 -0400
@@ -848,21 +848,18 @@
 EXPORT_SYMBOL(blk_queue_find_tag);
 
 /**
- * __blk_queue_free_tags - release tag maintenance info
- * @q:  the request queue for the device
+ * __blk_free_tags - release a given set of tag maintenance info
+ * @bqt:	the tag map to free
  *
- *  Notes:
- *    blk_cleanup_queue() will take care of calling this function, if tagging
- *    has been used. So there's no need to call this directly.
- **/
-static void __blk_queue_free_tags(request_queue_t *q)
+ * Tries to free the specified @bqt@.  Returns true if it was
+ * actually freed and false if there are still references using it
+ */
+static int __blk_free_tags(struct blk_queue_tag *bqt)
 {
-	struct blk_queue_tag *bqt = q->queue_tags;
+	int retval;
 
-	if (!bqt)
-		return;
-
-	if (atomic_dec_and_test(&bqt->refcnt)) {
+	retval = atomic_dec_and_test(&bqt->refcnt);
+	if (retval) {
 		BUG_ON(bqt->busy);
 		BUG_ON(!list_empty(&bqt->busy_list));
 
@@ -873,12 +870,49 @@
 		bqt->tag_map = NULL;
 
 		kfree(bqt);
+
 	}
 
+	return retval;
+}
+
+/**
+ * __blk_queue_free_tags - release tag maintenance info
+ * @q:  the request queue for the device
+ *
+ *  Notes:
+ *    blk_cleanup_queue() will take care of calling this function, if tagging
+ *    has been used. So there's no need to call this directly.
+ **/
+static void __blk_queue_free_tags(request_queue_t *q)
+{
+	struct blk_queue_tag *bqt = q->queue_tags;
+
+	if (!bqt)
+		return;
+
+	__blk_free_tags(bqt);
+
 	q->queue_tags = NULL;
 	q->queue_flags &= ~(1 << QUEUE_FLAG_QUEUED);
 }
 
+
+/**
+ * blk_free_tags - release a given set of tag maintenance info
+ * @bqt:	the tag map to free
+ *
+ * For externally managed @bqt@ frees the map.  Callers of this
+ * function must guarantee to have released all the queues that
+ * might have been using this tag map.
+ */
+void blk_free_tags(struct blk_queue_tag *bqt)
+{
+	if (unlikely(!__blk_free_tags(bqt)))
+		BUG();
+}
+EXPORT_SYMBOL(blk_free_tags);
+
 /**
  * blk_queue_free_tags - release tag maintenance info
  * @q:  the request queue for the device
@@ -901,7 +935,7 @@
 	unsigned long *tag_map;
 	int nr_ulongs;
 
-	if (depth > q->nr_requests * 2) {
+	if (q && depth > q->nr_requests * 2) {
 		depth = q->nr_requests * 2;
 		printk(KERN_ERR "%s: adjusted depth to %d\n",
 				__FUNCTION__, depth);
@@ -927,6 +961,38 @@
 	return -ENOMEM;
 }
 
+static struct blk_queue_tag *__blk_queue_init_tags(struct request_queue *q,
+						   int depth)
+{
+	struct blk_queue_tag *tags;
+
+	tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
+	if (!tags)
+		goto fail;
+
+	if (init_tag_map(q, tags, depth))
+		goto fail;
+
+	INIT_LIST_HEAD(&tags->busy_list);
+	tags->busy = 0;
+	atomic_set(&tags->refcnt, 1);
+	return tags;
+fail:
+	kfree(tags);
+	return NULL;
+}
+
+/**
+ * blk_init_tags - initialize the tag info for an external tag map
+ * @depth:	the maximum queue depth supported
+ * @tags: the tag to use
+ **/
+struct blk_queue_tag *blk_init_tags(int depth)
+{
+	return __blk_queue_init_tags(NULL, depth);
+}
+EXPORT_SYMBOL(blk_init_tags);
+
 /**
  * blk_queue_init_tags - initialize the queue tag info
  * @q:  the request queue for the device
@@ -941,16 +1007,10 @@
 	BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
 
 	if (!tags && !q->queue_tags) {
-		tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
-		if (!tags)
-			goto fail;
+		tags = __blk_queue_init_tags(q, depth);
 
-		if (init_tag_map(q, tags, depth))
+		if (!tags)
 			goto fail;
-
-		INIT_LIST_HEAD(&tags->busy_list);
-		tags->busy = 0;
-		atomic_set(&tags->refcnt, 1);
 	} else if (q->queue_tags) {
 		if ((rc = blk_queue_resize_tags(q, depth)))
 			return rc;
@@ -1002,6 +1062,13 @@
 	}
 
 	/*
+	 * Currently cannot replace a shared tag map with a new
+	 * one, so error out if this is the case
+	 */
+	if (atomic_read(&bqt->refcnt) != 1)
+		return -EBUSY;
+
+	/*
 	 * save the old state info, so we can copy it back
 	 */
 	tag_index = bqt->tag_index;
@@ -1101,11 +1168,16 @@
 		BUG();
 	}
 
-	tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
-	if (tag >= bqt->max_depth)
-		return 1;
+	/*
+	 * Protect against shared tag maps, as we may not have exclusive
+	 * access to the tag map.
+	 */
+	do {
+		tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
+		if (tag >= bqt->max_depth)
+			return 1;
 
-	__set_bit(tag, bqt->tag_map);
+	} while (test_and_set_bit(tag, bqt->tag_map));
 
 	rq->flags |= REQ_QUEUED;
 	rq->tag = tag;
diff -urN linux-2.6.18.x86_64/drivers/scsi/hosts.c linux-2.6.18.x86_64.stex1/drivers/scsi/hosts.c
--- linux-2.6.18.x86_64/drivers/scsi/hosts.c	2006-09-19 23:42:06.000000000 -0400
+++ linux-2.6.18.x86_64.stex1/drivers/scsi/hosts.c	2006-10-08 21:28:45.000000000 -0400
@@ -265,6 +265,9 @@
 		destroy_workqueue(shost->work_q);
 
 	scsi_destroy_command_freelist(shost);
+	if (shost->bqt)
+		blk_free_tags(shost->bqt);
+
 	kfree(shost->shost_data);
 
 	if (parent)
diff -urN linux-2.6.18.x86_64/include/linux/blkdev.h linux-2.6.18.x86_64.stex1/include/linux/blkdev.h
--- linux-2.6.18.x86_64/include/linux/blkdev.h	2006-09-19 23:42:06.000000000 -0400
+++ linux-2.6.18.x86_64.stex1/include/linux/blkdev.h	2006-10-08 21:28:46.000000000 -0400
@@ -746,6 +746,8 @@
 extern int blk_queue_resize_tags(request_queue_t *, int);
 extern void blk_queue_invalidate_tags(request_queue_t *);
 extern long blk_congestion_wait(int rw, long timeout);
+extern struct blk_queue_tag *blk_init_tags(int);
+extern void blk_free_tags(struct blk_queue_tag *);
 
 extern void blk_rq_bio_prep(request_queue_t *, struct request *, struct bio *);
 extern int blkdev_issue_flush(struct block_device *, sector_t *);
diff -urN linux-2.6.18.x86_64/include/scsi/scsi_host.h linux-2.6.18.x86_64.stex1/include/scsi/scsi_host.h
--- linux-2.6.18.x86_64/include/scsi/scsi_host.h	2006-09-19 23:42:06.000000000 -0400
+++ linux-2.6.18.x86_64.stex1/include/scsi/scsi_host.h	2006-10-08 21:28:45.000000000 -0400
@@ -16,6 +16,7 @@
 struct Scsi_Host;
 struct scsi_host_cmd_pool;
 struct scsi_transport_template;
+struct blk_queue_tags;
 
 
 /*
@@ -466,6 +467,12 @@
 	struct scsi_transport_template *transportt;
 
 	/*
+	 * area to keep a shared tag map (if needed, will be
+	 * NULL if not)
+	 */
+	struct blk_queue_tag	*bqt;
+
+	/*
 	 * The following two fields are protected with host_lock;
 	 * however, eh routines can safely access during eh processing
 	 * without acquiring the lock.
diff -urN linux-2.6.18.x86_64/include/scsi/scsi_tcq.h linux-2.6.18.x86_64.stex1/include/scsi/scsi_tcq.h
--- linux-2.6.18.x86_64/include/scsi/scsi_tcq.h	2006-09-19 23:42:06.000000000 -0400
+++ linux-2.6.18.x86_64.stex1/include/scsi/scsi_tcq.h	2006-10-08 21:28:48.000000000 -0400
@@ -4,6 +4,7 @@
 #include <linux/blkdev.h>
 #include <scsi/scsi_cmnd.h>
 #include <scsi/scsi_device.h>
+#include <scsi/scsi_host.h>
 
 
 #define MSG_SIMPLE_TAG	0x20
@@ -66,7 +67,8 @@
 		return;
 
 	if (!blk_queue_tagged(sdev->request_queue))
-		blk_queue_init_tags(sdev->request_queue, depth, NULL);
+		blk_queue_init_tags(sdev->request_queue, depth,
+				    sdev->host->bqt);
 
 	scsi_adjust_queue_depth(sdev, scsi_get_tag_type(sdev), depth);
 }
@@ -131,4 +133,15 @@
 	return sdev->current_cmnd;
 }
 
+/**
+ * scsi_init_shared_tag_map - create a shared tag map
+ * @shost:	the host to share the tag map among all devices
+ * @depth:	the total depth of the map
+ */
+static inline int scsi_init_shared_tag_map(struct Scsi_Host *shost, int depth)
+{
+	shost->bqt = blk_init_tags(depth);
+	return shost->bqt ? 0 : -ENOMEM;
+}
+
 #endif /* _SCSI_SCSI_TCQ_H */