[PATCH 2/3] md: Set MD_BROKEN for RAID1 and RAID10

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

There is no direct mechanism to determine raid failure outside
personality. It is done by checking rdev->flags after executing
md_error(). If "faulty" flag is not set then -EBUSY is returned to
userspace. -EBUSY means that array will be failed after drive removal.

Mdadm has special routine to handle the array failure and it is executed
if -EBUSY is returned by md.

There are at least two known reasons to not consider this mechanism
as correct:
1. drive can be removed even if array will be failed[1].
2. -EBUSY seems to be wrong status. Array is not busy, but removal
   process cannot proceed safe.

-EBUSY expectation cannot be removed without breaking compatibility
with userspace. In this patch first issue is resolved by adding support
for MD_BROKEN flag for RAID1 and RAID10. Support for RAID456 is added in
next commit.

The idea is to set the MD_BROKEN if we are sure that raid is in failed
state now. This is done in each error_handler(). In md_error() MD_BROKEN
flag is checked. If is set, then -EBUSY is returned to userspace.

As in previous commit, it causes that #mdadm --set-faulty is able to
fail array. Previously proposed workaround is valid if optional
functionality[1] is disabled.

[1] commit 9a567843f7ce("md: allow last device to be forcibly removed from
    RAID1/RAID10.")
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
---
 drivers/md/md.c     | 17 ++++++++-----
 drivers/md/md.h     | 62 +++++++++++++++++++++++++--------------------
 drivers/md/raid1.c  | 41 +++++++++++++++++-------------
 drivers/md/raid10.c | 33 ++++++++++++++++--------
 4 files changed, 91 insertions(+), 62 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index f888ef197765..fda8473f96b8 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2983,10 +2983,11 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
 
 	if (cmd_match(buf, "faulty") && rdev->mddev->pers) {
 		md_error(rdev->mddev, rdev);
-		if (test_bit(Faulty, &rdev->flags))
-			err = 0;
-		else
+
+		if (test_bit(MD_BROKEN, &rdev->mddev->flags))
 			err = -EBUSY;
+		else
+			err = 0;
 	} else if (cmd_match(buf, "remove")) {
 		if (rdev->mddev->pers) {
 			clear_bit(Blocked, &rdev->flags);
@@ -7441,7 +7442,7 @@ static int set_disk_faulty(struct mddev *mddev, dev_t dev)
 		err =  -ENODEV;
 	else {
 		md_error(mddev, rdev);
-		if (!test_bit(Faulty, &rdev->flags))
+		if (test_bit(MD_BROKEN, &mddev->flags))
 			err = -EBUSY;
 	}
 	rcu_read_unlock();
@@ -7987,12 +7988,14 @@ void md_error(struct mddev *mddev, struct md_rdev *rdev)
 	if (!mddev->pers->sync_request)
 		return;
 
-	if (mddev->degraded)
+	if (mddev->degraded && !test_bit(MD_BROKEN, &mddev->flags))
 		set_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
 	sysfs_notify_dirent_safe(rdev->sysfs_state);
 	set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
-	md_wakeup_thread(mddev->thread);
+	if (!test_bit(MD_BROKEN, &mddev->flags)) {
+		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+		md_wakeup_thread(mddev->thread);
+	}
 	if (mddev->event_work.func)
 		queue_work(md_misc_wq, &mddev->event_work);
 	md_new_event();
diff --git a/drivers/md/md.h b/drivers/md/md.h
index bc3f2094d0b6..1eb7d0e88cb2 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -234,34 +234,42 @@ extern int rdev_clear_badblocks(struct md_rdev *rdev, sector_t s, int sectors,
 				int is_new);
 struct md_cluster_info;
 
-/* change UNSUPPORTED_MDDEV_FLAGS for each array type if new flag is added */
+/**
+ * enum mddev_flags - md device flags.
+ * @MD_ARRAY_FIRST_USE: First use of array, needs initialization.
+ * @MD_CLOSING: If set, we are closing the array, do not open it then.
+ * @MD_JOURNAL_CLEAN: A raid with journal is already clean.
+ * @MD_HAS_JOURNAL: The raid array has journal feature set.
+ * @MD_CLUSTER_RESYNC_LOCKED: cluster raid only, which means node, already took
+ *			       resync lock, need to release the lock.
+ * @MD_FAILFAST_SUPPORTED: Using MD_FAILFAST on metadata writes is supported as
+ *			    calls to md_error() will never cause the array to
+ *			    become failed.
+ * @MD_HAS_PPL:  The raid array has PPL feature set.
+ * @MD_HAS_MULTIPLE_PPLS: The raid array has multiple PPLs feature set.
+ * @MD_ALLOW_SB_UPDATE: md_check_recovery is allowed to update the metadata
+ *			 without taking reconfig_mutex.
+ * @MD_UPDATING_SB: md_check_recovery is updating the metadata without
+ *		     explicitly holding reconfig_mutex.
+ * @MD_NOT_READY: do_md_run() is active, so 'array_state', ust not report that
+ *		   array is ready yet.
+ * @MD_BROKEN: This is used to stop writes and mark array as failed.
+ *
+ * change UNSUPPORTED_MDDEV_FLAGS for each array type if new flag is added
+ */
 enum mddev_flags {
-	MD_ARRAY_FIRST_USE,	/* First use of array, needs initialization */
-	MD_CLOSING,		/* If set, we are closing the array, do not open
-				 * it then */
-	MD_JOURNAL_CLEAN,	/* A raid with journal is already clean */
-	MD_HAS_JOURNAL,		/* The raid array has journal feature set */
-	MD_CLUSTER_RESYNC_LOCKED, /* cluster raid only, which means node
-				   * already took resync lock, need to
-				   * release the lock */
-	MD_FAILFAST_SUPPORTED,	/* Using MD_FAILFAST on metadata writes is
-				 * supported as calls to md_error() will
-				 * never cause the array to become failed.
-				 */
-	MD_HAS_PPL,		/* The raid array has PPL feature set */
-	MD_HAS_MULTIPLE_PPLS,	/* The raid array has multiple PPLs feature set */
-	MD_ALLOW_SB_UPDATE,	/* md_check_recovery is allowed to update
-				 * the metadata without taking reconfig_mutex.
-				 */
-	MD_UPDATING_SB,		/* md_check_recovery is updating the metadata
-				 * without explicitly holding reconfig_mutex.
-				 */
-	MD_NOT_READY,		/* do_md_run() is active, so 'array_state'
-				 * must not report that array is ready yet
-				 */
-	MD_BROKEN,              /* This is used in RAID-0/LINEAR only, to stop
-				 * I/O in case an array member is gone/failed.
-				 */
+	MD_ARRAY_FIRST_USE,
+	MD_CLOSING,
+	MD_JOURNAL_CLEAN,
+	MD_HAS_JOURNAL,
+	MD_CLUSTER_RESYNC_LOCKED,
+	MD_FAILFAST_SUPPORTED,
+	MD_HAS_PPL,
+	MD_HAS_MULTIPLE_PPLS,
+	MD_ALLOW_SB_UPDATE,
+	MD_UPDATING_SB,
+	MD_NOT_READY,
+	MD_BROKEN,
 };
 
 enum mddev_sb_flags {
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 7dc8026cf6ee..b222bafa1196 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1615,30 +1615,37 @@ static void raid1_status(struct seq_file *seq, struct mddev *mddev)
 	seq_printf(seq, "]");
 }
 
+/**
+ * raid1_error() - RAID1 error handler.
+ * @mddev: affected md device.
+ * @rdev: member device to remove.
+ *
+ * Error on @rdev is raised and it is needed to be removed from @mddev.
+ * If there are more than one active member, @rdev is always removed.
+ *
+ * If it is the last active member, it depends on &mddev->fail_last_dev:
+ * - if is on @rdev is removed.
+ * - if is off, @rdev is not removed, but recovery from it is disabled (@rdev is
+ *   very likely to fail).
+ * In both cases, &MD_BROKEN will be set in &mddev->flags.
+ */
 static void raid1_error(struct mddev *mddev, struct md_rdev *rdev)
 {
 	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
-	 * else if it is the last working disks with "fail_last_dev == false",
-	 * ignore the error, let the next level up know.
-	 * else mark the drive as failed
-	 */
 	spin_lock_irqsave(&conf->device_lock, flags);
-	if (test_bit(In_sync, &rdev->flags) && !mddev->fail_last_dev
-	    && (conf->raid_disks - mddev->degraded) == 1) {
-		/*
-		 * Don't fail the drive, act as though we were just a
-		 * normal single drive.
-		 * However don't try a recovery from this drive as
-		 * it is very likely to fail.
-		 */
-		conf->recovery_disabled = mddev->recovery_disabled;
-		spin_unlock_irqrestore(&conf->device_lock, flags);
-		return;
+
+	if (test_bit(In_sync, &rdev->flags) &&
+	    (conf->raid_disks - mddev->degraded) == 1) {
+		set_bit(MD_BROKEN, &mddev->flags);
+
+		if (!mddev->fail_last_dev) {
+			conf->recovery_disabled = mddev->recovery_disabled;
+			spin_unlock_irqrestore(&conf->device_lock, flags);
+			return;
+		}
 	}
 	set_bit(Blocked, &rdev->flags);
 	if (test_and_clear_bit(In_sync, &rdev->flags))
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index dde98f65bd04..7471e20d7cd6 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1945,26 +1945,37 @@ static int enough(struct r10conf *conf, int ignore)
 		_enough(conf, 1, ignore);
 }
 
+/**
+ * raid10_error() - RAID10 error handler.
+ * @mddev: affected md device.
+ * @rdev: member device to remove.
+ *
+ * Error on @rdev is raised and it is needed to be removed from @mddev.
+ * If there is (excluding @rdev) enough members to operate, @rdev is always
+ * removed.
+ *
+ * Otherwise, it depends on &mddev->fail_last_dev:
+ * - if is on @rdev is removed.
+ * - if is off, @rdev is not removed.
+ *
+ * In both cases, &MD_BROKEN will be set in &mddev->flags.
+ */
 static void raid10_error(struct mddev *mddev, struct md_rdev *rdev)
 {
 	char b[BDEVNAME_SIZE];
 	struct r10conf *conf = mddev->private;
 	unsigned long flags;
 
-	/*
-	 * If it is not operational, then we have already marked it as dead
-	 * else if it is the last working disks with "fail_last_dev == false",
-	 * ignore the error, let the next level up know.
-	 * else mark the drive as failed
-	 */
 	spin_lock_irqsave(&conf->device_lock, flags);
+
 	if (test_bit(In_sync, &rdev->flags) && !mddev->fail_last_dev
 	    && !enough(conf, rdev->raid_disk)) {
-		/*
-		 * Don't fail the drive, just return an IO error.
-		 */
-		spin_unlock_irqrestore(&conf->device_lock, flags);
-		return;
+		set_bit(MD_BROKEN, &mddev->flags);
+
+		if (!mddev->fail_last_dev) {
+			spin_unlock_irqrestore(&conf->device_lock, flags);
+			return;
+		}
 	}
 	if (test_and_clear_bit(In_sync, &rdev->flags))
 		mddev->degraded++;
-- 
2.26.2