X-Git-Url: https://git.karo-electronics.de/?a=blobdiff_plain;f=drivers%2Fmd%2Fraid5.c;h=a33dac7c2e2fb143d674a48b8ab19280cdd36dd8;hb=b5e98d65d34a1c11a2135ea8a9b2619dbc7216c8;hp=d89a25e7c17bb0d50b0bc78bb290877ddb31ea8a;hpb=d84e0f10d38393f617227f0c831a99c69294651f;p=karo-tx-linux.git

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index d89a25e7c17b..a33dac7c2e2f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1822,7 +1822,79 @@ static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
 	}
 }
 
+static int
+handle_write_operations5(struct stripe_head *sh, int rcw, int expand)
+{
+	int i, pd_idx = sh->pd_idx, disks = sh->disks;
+	int locked = 0;
+
+	if (rcw) {
+		/* if we are not expanding this is a proper write request, and
+		 * there will be bios with new data to be drained into the
+		 * stripe cache
+		 */
+		if (!expand) {
+			set_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);
+			sh->ops.count++;
+		}
+
+		set_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);
+		sh->ops.count++;
+
+		for (i = disks; i--; ) {
+			struct r5dev *dev = &sh->dev[i];
+
+			if (dev->towrite) {
+				set_bit(R5_LOCKED, &dev->flags);
+				if (!expand)
+					clear_bit(R5_UPTODATE, &dev->flags);
+				locked++;
+			}
+		}
+	} else {
+		BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||
+			test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));
 
+		set_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
+		set_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);
+		set_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);
+
+		sh->ops.count += 3;
+
+		for (i = disks; i--; ) {
+			struct r5dev *dev = &sh->dev[i];
+			if (i == pd_idx)
+				continue;
+
+			/* For a read-modify write there may be blocks that are
+			 * locked for reading while others are ready to be
+			 * written so we distinguish these blocks by the
+			 * R5_Wantprexor bit
+			 */
+			if (dev->towrite &&
+			    (test_bit(R5_UPTODATE, &dev->flags) ||
+			    test_bit(R5_Wantcompute, &dev->flags))) {
+				set_bit(R5_Wantprexor, &dev->flags);
+				set_bit(R5_LOCKED, &dev->flags);
+				clear_bit(R5_UPTODATE, &dev->flags);
+				locked++;
+			}
+		}
+	}
+
+	/* keep the parity disk locked while asynchronous operations
+	 * are in flight
+	 */
+	set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);
+	clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+	locked++;
+
+	pr_debug("%s: stripe %llu locked: %d pending: %lx\n",
+		__FUNCTION__, (unsigned long long)sh->sector,
+		locked, sh->ops.pending);
+
+	return locked;
+}
 
 /*
  * Each stripe/dev can have one or more bion attached.
@@ -1977,9 +2049,12 @@ handle_requests_to_failed_array(raid5_conf_t *conf, struct stripe_head *sh,
 			bi = bi2;
 		}
 
-		/* fail any reads if this device is non-operational */
-		if (!test_bit(R5_Insync, &sh->dev[i].flags) ||
-		    test_bit(R5_ReadError, &sh->dev[i].flags)) {
+		/* fail any reads if this device is non-operational and
+		 * the data has not reached the cache yet.
+		 */
+		if (!test_bit(R5_Wantfill, &sh->dev[i].flags) &&
+		    (!test_bit(R5_Insync, &sh->dev[i].flags) ||
+		      test_bit(R5_ReadError, &sh->dev[i].flags))) {
 			bi = sh->dev[i].toread;
 			sh->dev[i].toread = NULL;
 			if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
@@ -2005,36 +2080,101 @@ handle_requests_to_failed_array(raid5_conf_t *conf, struct stripe_head *sh,
 
 }
 
+/* __handle_issuing_new_read_requests5 - returns 0 if there are no more disks
+ * to process
+ */
+static int __handle_issuing_new_read_requests5(struct stripe_head *sh,
+			struct stripe_head_state *s, int disk_idx, int disks)
+{
+	struct r5dev *dev = &sh->dev[disk_idx];
+	struct r5dev *failed_dev = &sh->dev[s->failed_num];
+
+	/* don't schedule compute operations or reads on the parity block while
+	 * a check is in flight
+	 */
+	if ((disk_idx == sh->pd_idx) &&
+	     test_bit(STRIPE_OP_CHECK, &sh->ops.pending))
+		return ~0;
+
+	/* is the data in this block needed, and can we get it? */
+	if (!test_bit(R5_LOCKED, &dev->flags) &&
+	    !test_bit(R5_UPTODATE, &dev->flags) && (dev->toread ||
+	    (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
+	     s->syncing || s->expanding || (s->failed &&
+	     (failed_dev->toread || (failed_dev->towrite &&
+	     !test_bit(R5_OVERWRITE, &failed_dev->flags)
+	     ))))) {
+		/* 1/ We would like to get this block, possibly by computing it,
+		 * but we might not be able to.
+		 *
+		 * 2/ Since parity check operations potentially make the parity
+		 * block !uptodate it will need to be refreshed before any
+		 * compute operations on data disks are scheduled.
+		 *
+		 * 3/ We hold off parity block re-reads until check operations
+		 * have quiesced.
+		 */
+		if ((s->uptodate == disks - 1) &&
+		    !test_bit(STRIPE_OP_CHECK, &sh->ops.pending)) {
+			set_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending);
+			set_bit(R5_Wantcompute, &dev->flags);
+			sh->ops.target = disk_idx;
+			s->req_compute = 1;
+			sh->ops.count++;
+			/* Careful: from this point on 'uptodate' is in the eye
+			 * of raid5_run_ops which services 'compute' operations
+			 * before writes. R5_Wantcompute flags a block that will
+			 * be R5_UPTODATE by the time it is needed for a
+			 * subsequent operation.
+			 */
+			s->uptodate++;
+			return 0; /* uptodate + compute == disks */
+		} else if ((s->uptodate < disks - 1) &&
+			test_bit(R5_Insync, &dev->flags)) {
+			/* Note: we hold off compute operations while checks are
+			 * in flight, but we still prefer 'compute' over 'read'
+			 * hence we only read if (uptodate < * disks-1)
+			 */
+			set_bit(R5_LOCKED, &dev->flags);
+			set_bit(R5_Wantread, &dev->flags);
+			if (!test_and_set_bit(STRIPE_OP_IO, &sh->ops.pending))
+				sh->ops.count++;
+			s->locked++;
+			pr_debug("Reading block %d (sync=%d)\n", disk_idx,
+				s->syncing);
+		}
+	}
+
+	return ~0;
+}
+
 static void handle_issuing_new_read_requests5(struct stripe_head *sh,
 			struct stripe_head_state *s, int disks)
 {
 	int i;
-	for (i = disks; i--; ) {
-		struct r5dev *dev = &sh->dev[i];
-		if (!test_bit(R5_LOCKED, &dev->flags) &&
-		    !test_bit(R5_UPTODATE, &dev->flags) &&
-		    (dev->toread ||
-		     (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
-		     s->syncing || s->expanding ||
-		     (s->failed && (sh->dev[s->failed_num].toread ||
-			(sh->dev[s->failed_num].towrite &&
-			!test_bit(R5_OVERWRITE, &sh->dev[s->failed_num].flags))
-		      )))) {
-			/* we would like to get this block, possibly
-			 * by computing it, but we might not be able to
-			 */
-			if (s->uptodate == disks-1) {
-				pr_debug("Computing block %d\n", i);
-				compute_block(sh, i);
-				s->uptodate++;
-			} else if (test_bit(R5_Insync, &dev->flags)) {
-				set_bit(R5_LOCKED, &dev->flags);
-				set_bit(R5_Wantread, &dev->flags);
-				s->locked++;
-				pr_debug("Reading block %d (sync=%d)\n",
-					i, s->syncing);
-			}
-		}
+
+	/* Clear completed compute operations.  Parity recovery
+	 * (STRIPE_OP_MOD_REPAIR_PD) implies a write-back which is handled
+	 * later on in this routine
+	 */
+	if (test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete) &&
+		!test_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending)) {
+		clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete);
+		clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.ack);
+		clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending);
+	}
+
+	/* look for blocks to read/compute, skip this if a compute
+	 * is already in flight, or if the stripe contents are in the
+	 * midst of changing due to a write
+	 */
+	if (!test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending) &&
+		!test_bit(STRIPE_OP_PREXOR, &sh->ops.pending) &&
+		!test_bit(STRIPE_OP_POSTXOR, &sh->ops.pending)) {
+		for (i = disks; i--; )
+			if (__handle_issuing_new_read_requests5(
+				sh, s, i, disks) == 0)
+				break;
 	}
 	set_bit(STRIPE_HANDLE, &sh->state);
 }
@@ -2151,7 +2291,8 @@ static void handle_issuing_new_write_requests5(raid5_conf_t *conf,
 		struct r5dev *dev = &sh->dev[i];
 		if ((dev->towrite || i == sh->pd_idx) &&
 		    !test_bit(R5_LOCKED, &dev->flags) &&
-		    !test_bit(R5_UPTODATE, &dev->flags)) {
+		    !(test_bit(R5_UPTODATE, &dev->flags) ||
+		      test_bit(R5_Wantcompute, &dev->flags))) {
 			if (test_bit(R5_Insync, &dev->flags))
 				rmw++;
 			else
@@ -2160,9 +2301,9 @@ static void handle_issuing_new_write_requests5(raid5_conf_t *conf,
 		/* Would I have to read this buffer for reconstruct_write */
 		if (!test_bit(R5_OVERWRITE, &dev->flags) && i != sh->pd_idx &&
 		    !test_bit(R5_LOCKED, &dev->flags) &&
-		    !test_bit(R5_UPTODATE, &dev->flags)) {
-			if (test_bit(R5_Insync, &dev->flags))
-				rcw++;
+		    !(test_bit(R5_UPTODATE, &dev->flags) ||
+		    test_bit(R5_Wantcompute, &dev->flags))) {
+			if (test_bit(R5_Insync, &dev->flags)) rcw++;
 			else
 				rcw += 2*disks;
 		}
@@ -2176,7 +2317,8 @@ static void handle_issuing_new_write_requests5(raid5_conf_t *conf,
 			struct r5dev *dev = &sh->dev[i];
 			if ((dev->towrite || i == sh->pd_idx) &&
 			    !test_bit(R5_LOCKED, &dev->flags) &&
-			    !test_bit(R5_UPTODATE, &dev->flags) &&
+			    !(test_bit(R5_UPTODATE, &dev->flags) ||
+			    test_bit(R5_Wantcompute, &dev->flags)) &&
 			    test_bit(R5_Insync, &dev->flags)) {
 				if (
 				  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
@@ -2198,7 +2340,8 @@ static void handle_issuing_new_write_requests5(raid5_conf_t *conf,
 			if (!test_bit(R5_OVERWRITE, &dev->flags) &&
 			    i != sh->pd_idx &&
 			    !test_bit(R5_LOCKED, &dev->flags) &&
-			    !test_bit(R5_UPTODATE, &dev->flags) &&
+			    !(test_bit(R5_UPTODATE, &dev->flags) ||
+			    test_bit(R5_Wantcompute, &dev->flags)) &&
 			    test_bit(R5_Insync, &dev->flags)) {
 				if (
 				  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
@@ -2216,28 +2359,18 @@ static void handle_issuing_new_write_requests5(raid5_conf_t *conf,
 	/* now if nothing is locked, and if we have enough data,
 	 * we can start a write request
 	 */
-	if (s->locked == 0 && (rcw == 0 || rmw == 0) &&
-	    !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
-		pr_debug("Computing parity...\n");
-		compute_parity5(sh, rcw == 0 ?
-			RECONSTRUCT_WRITE : READ_MODIFY_WRITE);
-		/* now every locked buffer is ready to be written */
-		for (i = disks; i--; )
-			if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
-				pr_debug("Writing block %d\n", i);
-				s->locked++;
-				set_bit(R5_Wantwrite, &sh->dev[i].flags);
-				if (!test_bit(R5_Insync, &sh->dev[i].flags)
-				    || (i == sh->pd_idx && s->failed == 0))
-					set_bit(STRIPE_INSYNC, &sh->state);
-			}
-		if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
-			atomic_dec(&conf->preread_active_stripes);
-			if (atomic_read(&conf->preread_active_stripes) <
-			    IO_THRESHOLD)
-				md_wakeup_thread(conf->mddev->thread);
-		}
-	}
+	/* since handle_stripe can be called at any time we need to handle the
+	 * case where a compute block operation has been submitted and then a
+	 * subsequent call wants to start a write request.  raid5_run_ops only
+	 * handles the case where compute block and postxor are requested
+	 * simultaneously.  If this is not the case then new writes need to be
+	 * held off until the compute completes.
+	 */
+	if ((s->req_compute ||
+	    !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending)) &&
+		(s->locked == 0 && (rcw == 0 || rmw == 0) &&
+		!test_bit(STRIPE_BIT_DELAY, &sh->state)))
+		s->locked += handle_write_operations5(sh, rcw == 0, 0);
 }
 
 static void handle_issuing_new_write_requests6(raid5_conf_t *conf,
@@ -2341,26 +2474,67 @@ static void handle_parity_checks5(raid5_conf_t *conf, struct stripe_head *sh,
 				struct stripe_head_state *s, int disks)
 {
 	set_bit(STRIPE_HANDLE, &sh->state);
-	if (s->failed == 0) {
-		BUG_ON(s->uptodate != disks);
-		compute_parity5(sh, CHECK_PARITY);
-		s->uptodate--;
-		if (page_is_zero(sh->dev[sh->pd_idx].page)) {
-			/* parity is correct (on disc, not in buffer any more)
-			 */
-			set_bit(STRIPE_INSYNC, &sh->state);
-		} else {
-			conf->mddev->resync_mismatches += STRIPE_SECTORS;
-			if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
-				/* don't try to repair!! */
+	/* Take one of the following actions:
+	 * 1/ start a check parity operation if (uptodate == disks)
+	 * 2/ finish a check parity operation and act on the result
+	 * 3/ skip to the writeback section if we previously
+	 *    initiated a recovery operation
+	 */
+	if (s->failed == 0 &&
+	    !test_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending)) {
+		if (!test_and_set_bit(STRIPE_OP_CHECK, &sh->ops.pending)) {
+			BUG_ON(s->uptodate != disks);
+			clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
+			sh->ops.count++;
+			s->uptodate--;
+		} else if (
+		       test_and_clear_bit(STRIPE_OP_CHECK, &sh->ops.complete)) {
+			clear_bit(STRIPE_OP_CHECK, &sh->ops.ack);
+			clear_bit(STRIPE_OP_CHECK, &sh->ops.pending);
+
+			if (sh->ops.zero_sum_result == 0)
+				/* parity is correct (on disc,
+				 * not in buffer any more)
+				 */
 				set_bit(STRIPE_INSYNC, &sh->state);
 			else {
-				compute_block(sh, sh->pd_idx);
-				s->uptodate++;
+				conf->mddev->resync_mismatches +=
+					STRIPE_SECTORS;
+				if (test_bit(
+				     MD_RECOVERY_CHECK, &conf->mddev->recovery))
+					/* don't try to repair!! */
+					set_bit(STRIPE_INSYNC, &sh->state);
+				else {
+					set_bit(STRIPE_OP_COMPUTE_BLK,
+						&sh->ops.pending);
+					set_bit(STRIPE_OP_MOD_REPAIR_PD,
+						&sh->ops.pending);
+					set_bit(R5_Wantcompute,
+						&sh->dev[sh->pd_idx].flags);
+					sh->ops.target = sh->pd_idx;
+					sh->ops.count++;
+					s->uptodate++;
+				}
 			}
 		}
 	}
-	if (!test_bit(STRIPE_INSYNC, &sh->state)) {
+
+	/* check if we can clear a parity disk reconstruct */
+	if (test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete) &&
+		test_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending)) {
+
+		clear_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending);
+		clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete);
+		clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.ack);
+		clear_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending);
+	}
+
+	/* Wait for check parity and compute block operations to complete
+	 * before write-back
+	 */
+	if (!test_bit(STRIPE_INSYNC, &sh->state) &&
+		!test_bit(STRIPE_OP_CHECK, &sh->ops.pending) &&
+		!test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending)) {
 		struct r5dev *dev;
 		/* either failed parity check, or recovery is happening */
 		if (s->failed == 0)
@@ -2569,36 +2743,27 @@ static void handle_stripe5(struct stripe_head *sh)
 		struct r5dev *dev = &sh->dev[i];
 		clear_bit(R5_Insync, &dev->flags);
 
-		pr_debug("check %d: state 0x%lx read %p write %p written %p\n",
-			i, dev->flags, dev->toread, dev->towrite, dev->written);
-		/* maybe we can reply to a read */
-		if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
-			struct bio *rbi, *rbi2;
-			pr_debug("Return read for disc %d\n", i);
-			spin_lock_irq(&conf->device_lock);
-			rbi = dev->toread;
-			dev->toread = NULL;
-			if (test_and_clear_bit(R5_Overlap, &dev->flags))
-				wake_up(&conf->wait_for_overlap);
-			spin_unlock_irq(&conf->device_lock);
-			while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
-				copy_data(0, rbi, dev->page, dev->sector);
-				rbi2 = r5_next_bio(rbi, dev->sector);
-				spin_lock_irq(&conf->device_lock);
-				if (--rbi->bi_phys_segments == 0) {
-					rbi->bi_next = return_bi;
-					return_bi = rbi;
-				}
-				spin_unlock_irq(&conf->device_lock);
-				rbi = rbi2;
-			}
-		}
+		pr_debug("check %d: state 0x%lx toread %p read %p write %p "
+			"written %p\n",	i, dev->flags, dev->toread, dev->read,
+			dev->towrite, dev->written);
+
+		/* maybe we can request a biofill operation
+		 *
+		 * new wantfill requests are only permitted while
+		 * STRIPE_OP_BIOFILL is clear
+		 */
+		if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread &&
+			!test_bit(STRIPE_OP_BIOFILL, &sh->ops.pending))
+			set_bit(R5_Wantfill, &dev->flags);
 
 		/* now count some things */
 		if (test_bit(R5_LOCKED, &dev->flags)) s.locked++;
 		if (test_bit(R5_UPTODATE, &dev->flags)) s.uptodate++;
+		if (test_bit(R5_Wantcompute, &dev->flags)) s.compute++;
 
-		if (dev->toread)
+		if (test_bit(R5_Wantfill, &dev->flags))
+			s.to_fill++;
+		else if (dev->toread)
 			s.to_read++;
 		if (dev->towrite) {
 			s.to_write++;
@@ -2621,6 +2786,10 @@ static void handle_stripe5(struct stripe_head *sh)
 			set_bit(R5_Insync, &dev->flags);
 	}
 	rcu_read_unlock();
+
+	if (s.to_fill && !test_and_set_bit(STRIPE_OP_BIOFILL, &sh->ops.pending))
+		sh->ops.count++;
+
 	pr_debug("locked=%d uptodate=%d to_read=%d"
 		" to_write=%d failed=%d failed_num=%d\n",
 		s.locked, s.uptodate, s.to_read, s.to_write,
@@ -2653,20 +2822,88 @@ static void handle_stripe5(struct stripe_head *sh)
 	 * or to load a block that is being partially written.
 	 */
 	if (s.to_read || s.non_overwrite ||
-		(s.syncing && (s.uptodate < disks)) || s.expanding)
+	    (s.syncing && (s.uptodate + s.compute < disks)) || s.expanding ||
+	    test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending))
 		handle_issuing_new_read_requests5(sh, &s, disks);
 
-	/* now to consider writing and what else, if anything should be read */
-	if (s.to_write)
+	/* Now we check to see if any write operations have recently
+	 * completed
+	 */
+
+	/* leave prexor set until postxor is done, allows us to distinguish
+	 * a rmw from a rcw during biodrain
+	 */
+	if (test_bit(STRIPE_OP_PREXOR, &sh->ops.complete) &&
+		test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete)) {
+
+		clear_bit(STRIPE_OP_PREXOR, &sh->ops.complete);
+		clear_bit(STRIPE_OP_PREXOR, &sh->ops.ack);
+		clear_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
+
+		for (i = disks; i--; )
+			clear_bit(R5_Wantprexor, &sh->dev[i].flags);
+	}
+
+	/* if only POSTXOR is set then this is an 'expand' postxor */
+	if (test_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete) &&
+		test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete)) {
+
+		clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete);
+		clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.ack);
+		clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);
+
+		clear_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);
+		clear_bit(STRIPE_OP_POSTXOR, &sh->ops.ack);
+		clear_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);
+
+		/* All the 'written' buffers and the parity block are ready to
+		 * be written back to disk
+		 */
+		BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags));
+		for (i = disks; i--; ) {
+			dev = &sh->dev[i];
+			if (test_bit(R5_LOCKED, &dev->flags) &&
+				(i == sh->pd_idx || dev->written)) {
+				pr_debug("Writing block %d\n", i);
+				set_bit(R5_Wantwrite, &dev->flags);
+				if (!test_and_set_bit(
+				    STRIPE_OP_IO, &sh->ops.pending))
+					sh->ops.count++;
+				if (!test_bit(R5_Insync, &dev->flags) ||
+				    (i == sh->pd_idx && s.failed == 0))
+					set_bit(STRIPE_INSYNC, &sh->state);
+			}
+		}
+		if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
+			atomic_dec(&conf->preread_active_stripes);
+			if (atomic_read(&conf->preread_active_stripes) <
+				IO_THRESHOLD)
+				md_wakeup_thread(conf->mddev->thread);
+		}
+	}
+
+	/* Now to consider new write requests and what else, if anything
+	 * should be read.  We do not handle new writes when:
+	 * 1/ A 'write' operation (copy+xor) is already in flight.
+	 * 2/ A 'check' operation is in flight, as it may clobber the parity
+	 *    block.
+	 */
+	if (s.to_write && !test_bit(STRIPE_OP_POSTXOR, &sh->ops.pending) &&
+			  !test_bit(STRIPE_OP_CHECK, &sh->ops.pending))
 		handle_issuing_new_write_requests5(conf, sh, &s, disks);
 
 	/* maybe we need to check and possibly fix the parity for this stripe
-	 * Any reads will already have been scheduled, so we just see if enough data
-	 * is available
+	 * Any reads will already have been scheduled, so we just see if enough
+	 * data is available.  The parity check is held off while parity
+	 * dependent operations are in flight.
 	 */
-	if (s.syncing && s.locked == 0 &&
-	    !test_bit(STRIPE_INSYNC, &sh->state))
+	if ((s.syncing && s.locked == 0 &&
+	     !test_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending) &&
+	     !test_bit(STRIPE_INSYNC, &sh->state)) ||
+	      test_bit(STRIPE_OP_CHECK, &sh->ops.pending) ||
+	      test_bit(STRIPE_OP_MOD_REPAIR_PD, &sh->ops.pending))
 		handle_parity_checks5(conf, sh, &s, disks);
+
 	if (s.syncing && s.locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
 		md_done_sync(conf->mddev, STRIPE_SECTORS,1);
 		clear_bit(STRIPE_SYNCING, &sh->state);