[PATCH 3.2 008/107] md/raid1: extend spinlock to protect raid1_end_read_request against inconsistencies

[Ben Hutchings]

3.2.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: NeilBrown <neilb@xxxxxxxx>

commit 423f04d63cf421ea436bcc5be02543d549ce4b28 upstream.

raid1_end_read_request() assumes that the In_sync bits are consistent
with the ->degaded count.
raid1_spare_active updates the In_sync bit before the ->degraded count
and so exposes an inconsistency, as does error()
So extend the spinlock in raid1_spare_active() and error() to hide those
inconsistencies.

This should probably be part of
  Commit: 34cab6f42003 ("md/raid1: fix test for 'was read error from
  last working device'.")
as it addresses the same issue.  It fixes the same bug and should go
to -stable for same reasons.

Fixes: 76073054c95b ("md/raid1: clean up read_balance.")
Signed-off-by: NeilBrown <neilb@xxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/md/raid1.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1208,6 +1208,7 @@ static void error(struct mddev *mddev, s
 {
 	char b[BDEVNAME_SIZE];
 	struct r1conf *conf = mddev->private;
+	unsigned long flags;
 
 	/*
 	 * If it is not operational, then we have already marked it as dead
@@ -1227,14 +1228,13 @@ static void error(struct mddev *mddev, s
 		return;
 	}
 	set_bit(Blocked, &rdev->flags);
+	spin_lock_irqsave(&conf->device_lock, flags);
 	if (test_and_clear_bit(In_sync, &rdev->flags)) {
-		unsigned long flags;
-		spin_lock_irqsave(&conf->device_lock, flags);
 		mddev->degraded++;
 		set_bit(Faulty, &rdev->flags);
-		spin_unlock_irqrestore(&conf->device_lock, flags);
 	} else
 		set_bit(Faulty, &rdev->flags);
+	spin_unlock_irqrestore(&conf->device_lock, flags);
 	/*
 	 * if recovery is running, make sure it aborts.
 	 */
@@ -1292,7 +1292,10 @@ static int raid1_spare_active(struct mdd
 	 * Find all failed disks within the RAID1 configuration 
 	 * and mark them readable.
 	 * Called under mddev lock, so rcu protection not needed.
+	 * device_lock used to avoid races with raid1_end_read_request
+	 * which expects 'In_sync' flags and ->degraded to be consistent.
 	 */
+	spin_lock_irqsave(&conf->device_lock, flags);
 	for (i = 0; i < conf->raid_disks; i++) {
 		struct md_rdev *rdev = conf->mirrors[i].rdev;
 		if (rdev
@@ -1302,7 +1305,6 @@ static int raid1_spare_active(struct mdd
 			sysfs_notify_dirent_safe(rdev->sysfs_state);
 		}
 	}
-	spin_lock_irqsave(&conf->device_lock, flags);
 	mddev->degraded -= count;
 	spin_unlock_irqrestore(&conf->device_lock, flags);
 

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