Date:	Thu, 24 Aug 2006 17:20:24 +1000
From:	NeilBrown <neilb@...e.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 002 of 2] md: replace magic numbers in sb_dirty with well defined bit flags


From: NeilBrown <neilb@...e.de>

Instead of magic numbers (0,1,2,3) in sb_dirty, we have
some flags instead:
MD_CHANGE_DEVS
   Some device state has changed requiring superblock update
   on all devices.
MD_CHANGE_CLEAN
   The array has transitions from 'clean' to 'dirty' or back,
   requiring a superblock update on active devices, but possibly
   not on spares
MD_CHANGE_PENDING
   A superblock update is underway.

We wait for an update to complete by waiting for all flags to be clear.  A
flag can be set at any time, even during an update, without risk that the
change will be lost.

Stop exporting md_update_sb - isn't needed.

Signed-off-by: Neil Brown <neilb@...e.de>
Signed-off-by: Andrew Morton <akpm@...l.org>
Avoid backward event updates in md superblock when degraded.

If we
  - shut down a clean array,
  - restart with one (or more) drive(s) missing
  - make some changes
  - pause, so that they array gets marked 'clean',
the event count on the superblock of included drives
will be the same as that of the removed drives.
So adding the removed drive back in will cause it
to be included with no resync.

To avoid this, we only update the eventcount backwards when the array
is not degraded.  In this case there can (should) be no non-connected
drives that we can get confused with, and this is the particular case
where updating-backwards is valuable.


Signed-off-by: Neil Brown <neilb@...e.de>

### Diffstat output
 ./drivers/md/md.c           |   76 +++++++++++++++++++++++---------------------
 ./drivers/md/multipath.c    |    3 -
 ./drivers/md/raid1.c        |    2 -
 ./drivers/md/raid10.c       |    2 -
 ./drivers/md/raid5.c        |    8 ++--
 ./include/linux/raid/md.h   |    1 
 ./include/linux/raid/md_k.h |    6 ++-
 7 files changed, 52 insertions(+), 46 deletions(-)

diff .prev/drivers/md/md.c ./drivers/md/md.c
--- .prev/drivers/md/md.c	2006-08-24 17:03:47.000000000 +1000
+++ ./drivers/md/md.c	2006-08-24 17:06:12.000000000 +1000
@@ -1587,7 +1587,7 @@ static void sync_sbs(mddev_t * mddev, in
 	}
 }
 
-void md_update_sb(mddev_t * mddev)
+static void md_update_sb(mddev_t * mddev, int force_change)
 {
 	int err;
 	struct list_head *tmp;
@@ -1598,7 +1598,18 @@ void md_update_sb(mddev_t * mddev)
 repeat:
 	spin_lock_irq(&mddev->write_lock);
 
-	if (mddev->degraded && mddev->sb_dirty == 3)
+	set_bit(MD_CHANGE_PENDING, &mddev->flags);
+	if (test_and_clear_bit(MD_CHANGE_DEVS, &mddev->flags))
+		force_change = 1;
+	if (test_and_clear_bit(MD_CHANGE_CLEAN, &mddev->flags))
+		/* just a clean<-> dirty transition, possibly leave spares alone,
+		 * though if events isn't the right even/odd, we will have to do
+		 * spares after all
+		 */
+		nospares = 1;
+	if (force_change)
+		nospares = 0;
+	if (mddev->degraded)
 		/* If the array is degraded, then skipping spares is both
 		 * dangerous and fairly pointless.
 		 * Dangerous because a device that was removed from the array
@@ -1608,20 +1619,14 @@ repeat:
 		 * then a recovery will happen and soon that array won't
 		 * be degraded any more and the spare can go back to sleep then.
 		 */
-		mddev->sb_dirty = 1;
+		nospares = 0;
 
 	sync_req = mddev->in_sync;
 	mddev->utime = get_seconds();
-	if (mddev->sb_dirty == 3)
-		/* just a clean<-> dirty transition, possibly leave spares alone,
-		 * though if events isn't the right even/odd, we will have to do
-		 * spares after all
-		 */
-		nospares = 1;
 
 	/* If this is just a dirty<->clean transition, and the array is clean
 	 * and 'events' is odd, we can roll back to the previous clean state */
-	if (mddev->sb_dirty == 3
+	if (nospares
 	    && (mddev->in_sync && mddev->recovery_cp == MaxSector)
 	    && (mddev->events & 1))
 		mddev->events--;
@@ -1652,7 +1657,6 @@ repeat:
 		MD_BUG();
 		mddev->events --;
 	}
-	mddev->sb_dirty = 2;
 	sync_sbs(mddev, nospares);
 
 	/*
@@ -1660,7 +1664,7 @@ repeat:
 	 * nonpersistent superblocks
 	 */
 	if (!mddev->persistent) {
-		mddev->sb_dirty = 0;
+		clear_bit(MD_CHANGE_PENDING, &mddev->flags);
 		spin_unlock_irq(&mddev->write_lock);
 		wake_up(&mddev->sb_wait);
 		return;
@@ -1697,20 +1701,20 @@ repeat:
 			break;
 	}
 	md_super_wait(mddev);
-	/* if there was a failure, sb_dirty was set to 1, and we re-write super */
+	/* if there was a failure, MD_CHANGE_DEVS was set, and we re-write super */
 
 	spin_lock_irq(&mddev->write_lock);
-	if (mddev->in_sync != sync_req|| mddev->sb_dirty == 1) {
+	if (mddev->in_sync != sync_req ||
+	    test_bit(MD_CHANGE_DEVS, &mddev->flags)) {
 		/* have to write it out again */
 		spin_unlock_irq(&mddev->write_lock);
 		goto repeat;
 	}
-	mddev->sb_dirty = 0;
+	clear_bit(MD_CHANGE_PENDING, &mddev->flags);
 	spin_unlock_irq(&mddev->write_lock);
 	wake_up(&mddev->sb_wait);
 
 }
-EXPORT_SYMBOL_GPL(md_update_sb);
 
 /* words written to sysfs files may, or my not, be \n terminated.
  * We want to accept with case. For this we use cmd_match.
@@ -1783,7 +1787,7 @@ state_store(mdk_rdev_t *rdev, const char
 		else {
 			mddev_t *mddev = rdev->mddev;
 			kick_rdev_from_array(rdev);
-			md_update_sb(mddev);
+			md_update_sb(mddev, 1);
 			md_new_event(mddev);
 			err = 0;
 		}
@@ -2426,7 +2430,7 @@ array_state_store(mddev_t *mddev, const 
 			spin_lock_irq(&mddev->write_lock);
 			if (atomic_read(&mddev->writes_pending) == 0) {
 				mddev->in_sync = 1;
-				mddev->sb_dirty = 1;
+				set_bit(MD_CHANGE_CLEAN, &mddev->flags);
 			}
 			spin_unlock_irq(&mddev->write_lock);
 		} else {
@@ -2438,7 +2442,7 @@ array_state_store(mddev_t *mddev, const 
 	case active:
 		if (mddev->pers) {
 			restart_array(mddev);
-			mddev->sb_dirty = 0;
+			clear_bit(MD_CHANGE_CLEAN, &mddev->flags);
 			wake_up(&mddev->sb_wait);
 			err = 0;
 		} else {
@@ -2543,7 +2547,7 @@ size_store(mddev_t *mddev, const char *b
 
 	if (mddev->pers) {
 		err = update_size(mddev, size);
-		md_update_sb(mddev);
+		md_update_sb(mddev, 1);
 	} else {
 		if (mddev->size == 0 ||
 		    mddev->size > size)
@@ -3111,8 +3115,8 @@ static int do_md_run(mddev_t * mddev)
 	
 	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
 	
-	if (mddev->sb_dirty)
-		md_update_sb(mddev);
+	if (mddev->flags)
+		md_update_sb(mddev, 0);
 
 	set_capacity(disk, mddev->array_size<<1);
 
@@ -3275,10 +3279,10 @@ static int do_md_stop(mddev_t * mddev, i
 			if (mddev->ro)
 				mddev->ro = 0;
 		}
-		if (!mddev->in_sync || mddev->sb_dirty) {
+		if (!mddev->in_sync || mddev->flags) {
 			/* mark array as shutdown cleanly */
 			mddev->in_sync = 1;
-			md_update_sb(mddev);
+			md_update_sb(mddev, 1);
 		}
 		if (mode == 1)
 			set_disk_ro(disk, 1);
@@ -3747,7 +3751,7 @@ static int hot_remove_disk(mddev_t * mdd
 		goto busy;
 
 	kick_rdev_from_array(rdev);
-	md_update_sb(mddev);
+	md_update_sb(mddev, 1);
 	md_new_event(mddev);
 
 	return 0;
@@ -3824,7 +3828,7 @@ static int hot_add_disk(mddev_t * mddev,
 
 	rdev->raid_disk = -1;
 
-	md_update_sb(mddev);
+	md_update_sb(mddev, 1);
 
 	/*
 	 * Kick recovery, maybe this spare has to be added to the
@@ -3955,7 +3959,8 @@ static int set_array_info(mddev_t * mdde
 
 	mddev->max_disks     = MD_SB_DISKS;
 
-	mddev->sb_dirty      = 1;
+	mddev->flags         = 0;
+	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 
 	mddev->default_bitmap_offset = MD_SB_BYTES >> 9;
 	mddev->bitmap_offset = 0;
@@ -4124,7 +4129,7 @@ static int update_array_info(mddev_t *md
 			mddev->bitmap_offset = 0;
 		}
 	}
-	md_update_sb(mddev);
+	md_update_sb(mddev, 1);
 	return rv;
 }
 
@@ -4960,12 +4965,12 @@ void md_write_start(mddev_t *mddev, stru
 		spin_lock_irq(&mddev->write_lock);
 		if (mddev->in_sync) {
 			mddev->in_sync = 0;
-			mddev->sb_dirty = 3;
+			set_bit(MD_CHANGE_CLEAN, &mddev->flags);
 			md_wakeup_thread(mddev->thread);
 		}
 		spin_unlock_irq(&mddev->write_lock);
 	}
-	wait_event(mddev->sb_wait, mddev->sb_dirty==0);
+	wait_event(mddev->sb_wait, mddev->flags==0);
 }
 
 void md_write_end(mddev_t *mddev)
@@ -5235,7 +5240,6 @@ void md_do_sync(mddev_t *mddev)
 				    !test_bit(In_sync, &rdev->flags) &&
 				    rdev->recovery_offset < mddev->curr_resync)
 					rdev->recovery_offset = mddev->curr_resync;
-			mddev->sb_dirty = 1;
 		}
 	}
 
@@ -5292,7 +5296,7 @@ void md_check_recovery(mddev_t *mddev)
 	}
 
 	if ( ! (
-		mddev->sb_dirty ||
+		mddev->flags ||
 		test_bit(MD_RECOVERY_NEEDED, &mddev->recovery) ||
 		test_bit(MD_RECOVERY_DONE, &mddev->recovery) ||
 		(mddev->safemode == 1) ||
@@ -5308,14 +5312,14 @@ void md_check_recovery(mddev_t *mddev)
 		if (mddev->safemode && !atomic_read(&mddev->writes_pending) &&
 		    !mddev->in_sync && mddev->recovery_cp == MaxSector) {
 			mddev->in_sync = 1;
-			mddev->sb_dirty = 3;
+			set_bit(MD_CHANGE_CLEAN, &mddev->flags);
 		}
 		if (mddev->safemode == 1)
 			mddev->safemode = 0;
 		spin_unlock_irq(&mddev->write_lock);
 
-		if (mddev->sb_dirty)
-			md_update_sb(mddev);
+		if (mddev->flags)
+			md_update_sb(mddev, 0);
 
 
 		if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
@@ -5334,7 +5338,7 @@ void md_check_recovery(mddev_t *mddev)
 				/* activate any spares */
 				mddev->pers->spare_active(mddev);
 			}
-			md_update_sb(mddev);
+			md_update_sb(mddev, 1);
 
 			/* if array is no-longer degraded, then any saved_raid_disk
 			 * information must be scrapped

diff .prev/drivers/md/multipath.c ./drivers/md/multipath.c
--- .prev/drivers/md/multipath.c	2006-08-24 17:03:33.000000000 +1000
+++ ./drivers/md/multipath.c	2006-08-24 17:04:03.000000000 +1000
@@ -253,7 +253,7 @@ static void multipath_error (mddev_t *md
 			char b[BDEVNAME_SIZE];
 			clear_bit(In_sync, &rdev->flags);
 			set_bit(Faulty, &rdev->flags);
-			mddev->sb_dirty = 1;
+			set_bit(MD_CHANGE_DEVS, &mddev->flags);
 			conf->working_disks--;
 			printk(KERN_ALERT "multipath: IO failure on %s,"
 				" disabling IO path. \n	Operation continuing"
@@ -470,7 +470,6 @@ static int multipath_run (mddev_t *mddev
 	}
 
 	conf->raid_disks = mddev->raid_disks;
-	mddev->sb_dirty = 1;
 	conf->mddev = mddev;
 	spin_lock_init(&conf->device_lock);
 	INIT_LIST_HEAD(&conf->retry_list);

diff .prev/drivers/md/raid1.c ./drivers/md/raid1.c
--- .prev/drivers/md/raid1.c	2006-08-24 17:03:33.000000000 +1000
+++ ./drivers/md/raid1.c	2006-08-24 17:04:03.000000000 +1000
@@ -966,7 +966,7 @@ static void error(mddev_t *mddev, mdk_rd
 	}
 	clear_bit(In_sync, &rdev->flags);
 	set_bit(Faulty, &rdev->flags);
-	mddev->sb_dirty = 1;
+	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 	printk(KERN_ALERT "raid1: Disk failure on %s, disabling device. \n"
 		"	Operation continuing on %d devices\n",
 		bdevname(rdev->bdev,b), conf->working_disks);

diff .prev/drivers/md/raid10.c ./drivers/md/raid10.c
--- .prev/drivers/md/raid10.c	2006-08-24 17:03:33.000000000 +1000
+++ ./drivers/md/raid10.c	2006-08-24 17:04:03.000000000 +1000
@@ -960,7 +960,7 @@ static void error(mddev_t *mddev, mdk_rd
 	}
 	clear_bit(In_sync, &rdev->flags);
 	set_bit(Faulty, &rdev->flags);
-	mddev->sb_dirty = 1;
+	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 	printk(KERN_ALERT "raid10: Disk failure on %s, disabling device. \n"
 		"	Operation continuing on %d devices\n",
 		bdevname(rdev->bdev,b), conf->working_disks);

diff .prev/drivers/md/raid5.c ./drivers/md/raid5.c
--- .prev/drivers/md/raid5.c	2006-08-24 17:03:33.000000000 +1000
+++ ./drivers/md/raid5.c	2006-08-24 17:04:03.000000000 +1000
@@ -696,7 +696,7 @@ static void error(mddev_t *mddev, mdk_rd
 	PRINTK("raid5: error called\n");
 
 	if (!test_bit(Faulty, &rdev->flags)) {
-		mddev->sb_dirty = 1;
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
 		if (test_bit(In_sync, &rdev->flags)) {
 			conf->working_disks--;
 			mddev->degraded++;
@@ -2781,9 +2781,9 @@ static sector_t reshape_request(mddev_t 
 		wait_event(conf->wait_for_overlap,
 			   atomic_read(&conf->reshape_stripes)==0);
 		mddev->reshape_position = conf->expand_progress;
-		mddev->sb_dirty = 1;
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
 		md_wakeup_thread(mddev->thread);
-		wait_event(mddev->sb_wait, mddev->sb_dirty == 0 ||
+		wait_event(mddev->sb_wait, mddev->flags == 0 ||
 			   kthread_should_stop());
 		spin_lock_irq(&conf->device_lock);
 		conf->expand_lo = mddev->reshape_position;
@@ -3605,7 +3605,7 @@ static int raid5_start_reshape(mddev_t *
 	mddev->degraded = (conf->raid_disks - conf->previous_raid_disks) - added_devices;
 	mddev->raid_disks = conf->raid_disks;
 	mddev->reshape_position = 0;
-	mddev->sb_dirty = 1;
+	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 
 	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);

diff .prev/include/linux/raid/md.h ./include/linux/raid/md.h
--- .prev/include/linux/raid/md.h	2006-08-24 17:03:33.000000000 +1000
+++ ./include/linux/raid/md.h	2006-08-24 17:04:03.000000000 +1000
@@ -93,7 +93,6 @@ extern int sync_page_io(struct block_dev
 extern void md_do_sync(mddev_t *mddev);
 extern void md_new_event(mddev_t *mddev);
 
-extern void md_update_sb(mddev_t * mddev);
 
 #endif 
 

diff .prev/include/linux/raid/md_k.h ./include/linux/raid/md_k.h
--- .prev/include/linux/raid/md_k.h	2006-08-24 17:03:33.000000000 +1000
+++ ./include/linux/raid/md_k.h	2006-08-24 17:04:03.000000000 +1000
@@ -114,7 +114,11 @@ struct mddev_s
 	dev_t				unit;
 	int				md_minor;
 	struct list_head 		disks;
-	int				sb_dirty;
+	unsigned long			flags;
+#define MD_CHANGE_DEVS	0	/* Some device status has changed */
+#define MD_CHANGE_CLEAN 1	/* transition to or from 'clean' */
+#define MD_CHANGE_PENDING 2	/* superblock update in progress */
+
 	int				ro;
 
 	struct gendisk			*gendisk;
-
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