diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 56ad453..004be80 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -645,7 +645,7 @@
 {
 	unsigned int nr_reads = 0, nr_writes = 0;
 	unsigned int max_nr_reads = throtl_grp_quantum*3/4;
-	unsigned int max_nr_writes = throtl_grp_quantum - nr_reads;
+	unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
 	struct bio *bio;
 
 	/* Try to dispatch 75% READS and 25% WRITES */
diff --git a/drivers/block/amiflop.c b/drivers/block/amiflop.c
index a1725e6..7888501 100644
--- a/drivers/block/amiflop.c
+++ b/drivers/block/amiflop.c
@@ -1341,7 +1341,7 @@
 {
 	struct request_queue *q;
 	int cnt = FD_MAX_UNITS;
-	struct request *rq;
+	struct request *rq = NULL;
 
 	/* Find next queue we can dispatch from */
 	fdc_queue = fdc_queue + 1;
diff --git a/drivers/block/ataflop.c b/drivers/block/ataflop.c
index 4e4cc6c..605a67e 100644
--- a/drivers/block/ataflop.c
+++ b/drivers/block/ataflop.c
@@ -1399,7 +1399,7 @@
 {
 	struct request_queue *q;
 	int old_pos = fdc_queue;
-	struct request *rq;
+	struct request *rq = NULL;
 
 	do {
 		q = unit[fdc_queue].disk->queue;
diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
index a67d0a6..f291587 100644
--- a/drivers/block/cciss.c
+++ b/drivers/block/cciss.c
@@ -66,6 +66,7 @@
 MODULE_LICENSE("GPL");
 
 static DEFINE_MUTEX(cciss_mutex);
+static struct proc_dir_entry *proc_cciss;
 
 #include "cciss_cmd.h"
 #include "cciss.h"
@@ -363,8 +364,6 @@
 #define ENG_GIG_FACTOR (ENG_GIG/512)
 #define ENGAGE_SCSI	"engage scsi"
 
-static struct proc_dir_entry *proc_cciss;
-
 static void cciss_seq_show_header(struct seq_file *seq)
 {
 	ctlr_info_t *h = seq->private;
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 255035c..4f9e22f 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -65,7 +65,7 @@
 
 struct blk_shadow {
 	struct blkif_request req;
-	unsigned long request;
+	struct request *request;
 	unsigned long frame[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 };
 
@@ -136,7 +136,7 @@
 			       unsigned long id)
 {
 	info->shadow[id].req.id  = info->shadow_free;
-	info->shadow[id].request = 0;
+	info->shadow[id].request = NULL;
 	info->shadow_free = id;
 }
 
@@ -245,14 +245,11 @@
 }
 
 /*
- * blkif_queue_request
+ * Generate a Xen blkfront IO request from a blk layer request.  Reads
+ * and writes are handled as expected.  Since we lack a loose flush
+ * request, we map flushes into a full ordered barrier.
  *
- * request block io
- *
- * id: for guest use only.
- * operation: BLKIF_OP_{READ,WRITE,PROBE}
- * buffer: buffer to read/write into. this should be a
- *   virtual address in the guest os.
+ * @req: a request struct
  */
 static int blkif_queue_request(struct request *req)
 {
@@ -281,7 +278,7 @@
 	/* Fill out a communications ring structure. */
 	ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
 	id = get_id_from_freelist(info);
-	info->shadow[id].request = (unsigned long)req;
+	info->shadow[id].request = req;
 
 	ring_req->id = id;
 	ring_req->sector_number = (blkif_sector_t)blk_rq_pos(req);
@@ -290,6 +287,18 @@
 	ring_req->operation = rq_data_dir(req) ?
 		BLKIF_OP_WRITE : BLKIF_OP_READ;
 
+	if (req->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
+		/*
+		 * Ideally we could just do an unordered
+		 * flush-to-disk, but all we have is a full write
+		 * barrier at the moment.  However, a barrier write is
+		 * a superset of FUA, so we can implement it the same
+		 * way.  (It's also a FLUSH+FUA, since it is
+		 * guaranteed ordered WRT previous writes.)
+		 */
+		ring_req->operation = BLKIF_OP_WRITE_BARRIER;
+	}
+
 	ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
 	BUG_ON(ring_req->nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
 
@@ -634,7 +643,7 @@
 
 		bret = RING_GET_RESPONSE(&info->ring, i);
 		id   = bret->id;
-		req  = (struct request *)info->shadow[id].request;
+		req  = info->shadow[id].request;
 
 		blkif_completion(&info->shadow[id]);
 
@@ -647,6 +656,16 @@
 				printk(KERN_WARNING "blkfront: %s: write barrier op failed\n",
 				       info->gd->disk_name);
 				error = -EOPNOTSUPP;
+			}
+			if (unlikely(bret->status == BLKIF_RSP_ERROR &&
+				     info->shadow[id].req.nr_segments == 0)) {
+				printk(KERN_WARNING "blkfront: %s: empty write barrier op failed\n",
+				       info->gd->disk_name);
+				error = -EOPNOTSUPP;
+			}
+			if (unlikely(error)) {
+				if (error == -EOPNOTSUPP)
+					error = 0;
 				info->feature_flush = 0;
 				xlvbd_flush(info);
 			}
@@ -899,7 +918,7 @@
 	/* Stage 3: Find pending requests and requeue them. */
 	for (i = 0; i < BLK_RING_SIZE; i++) {
 		/* Not in use? */
-		if (copy[i].request == 0)
+		if (!copy[i].request)
 			continue;
 
 		/* Grab a request slot and copy shadow state into it. */
@@ -916,9 +935,7 @@
 				req->seg[j].gref,
 				info->xbdev->otherend_id,
 				pfn_to_mfn(info->shadow[req->id].frame[j]),
-				rq_data_dir(
-					(struct request *)
-					info->shadow[req->id].request));
+				rq_data_dir(info->shadow[req->id].request));
 		info->shadow[req->id].req = *req;
 
 		info->ring.req_prod_pvt++;
@@ -1067,14 +1084,8 @@
 	 */
 	info->feature_flush = 0;
 
-	/*
-	 * The driver doesn't properly handled empty flushes, so
-	 * lets disable barrier support for now.
-	 */
-#if 0
 	if (!err && barrier)
-		info->feature_flush = REQ_FLUSH;
-#endif
+		info->feature_flush = REQ_FLUSH | REQ_FUA;
 
 	err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
 	if (err) {
diff --git a/fs/ioprio.c b/fs/ioprio.c
index 2f7d05c..7da2a06 100644
--- a/fs/ioprio.c
+++ b/fs/ioprio.c
@@ -103,22 +103,15 @@
 	}
 
 	ret = -ESRCH;
-	/*
-	 * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
-	 * so we can't use rcu_read_lock(). See re-copy of ->ioprio
-	 * in copy_process().
-	 */
-	read_lock(&tasklist_lock);
+	rcu_read_lock();
 	switch (which) {
 		case IOPRIO_WHO_PROCESS:
-			rcu_read_lock();
 			if (!who)
 				p = current;
 			else
 				p = find_task_by_vpid(who);
 			if (p)
 				ret = set_task_ioprio(p, ioprio);
-			rcu_read_unlock();
 			break;
 		case IOPRIO_WHO_PGRP:
 			if (!who)
@@ -141,12 +134,7 @@
 				break;
 
 			do_each_thread(g, p) {
-				int match;
-
-				rcu_read_lock();
-				match = __task_cred(p)->uid == who;
-				rcu_read_unlock();
-				if (!match)
+				if (__task_cred(p)->uid != who)
 					continue;
 				ret = set_task_ioprio(p, ioprio);
 				if (ret)
@@ -160,7 +148,7 @@
 			ret = -EINVAL;
 	}
 
-	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 	return ret;
 }
 
@@ -204,17 +192,15 @@
 	int ret = -ESRCH;
 	int tmpio;
 
-	read_lock(&tasklist_lock);
+	rcu_read_lock();
 	switch (which) {
 		case IOPRIO_WHO_PROCESS:
-			rcu_read_lock();
 			if (!who)
 				p = current;
 			else
 				p = find_task_by_vpid(who);
 			if (p)
 				ret = get_task_ioprio(p);
-			rcu_read_unlock();
 			break;
 		case IOPRIO_WHO_PGRP:
 			if (!who)
@@ -241,12 +227,7 @@
 				break;
 
 			do_each_thread(g, p) {
-				int match;
-
-				rcu_read_lock();
-				match = __task_cred(p)->uid == user->uid;
-				rcu_read_unlock();
-				if (!match)
+				if (__task_cred(p)->uid != user->uid)
 					continue;
 				tmpio = get_task_ioprio(p);
 				if (tmpio < 0)
@@ -264,6 +245,6 @@
 			ret = -EINVAL;
 	}
 
-	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 	return ret;
 }