[PATCH AUTOSEL 4.19 18/22] md: Whenassemble the array, consult the superblock of the freshest device

[Sasha Levin <sashal@kernel.org>]

From: Alex Lyakas <alex.lyakas@zadara.com>

[ Upstream commit dc1cc22ed58f11d58d8553c5ec5f11cbfc3e3039 ]

Upon assembling the array, both kernel and mdadm allow the devices to have event
counter difference of 1, and still consider them as up-to-date.
However, a device whose event count is behind by 1, may in fact not be up-to-date,
and array resync with such a device may cause data corruption.
To avoid this, consult the superblock of the freshest device about the status
of a device, whose event counter is behind by 1.

Signed-off-by: Alex Lyakas <alex.lyakas@zadara.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/1702470271-16073-1-git-send-email-alex.lyakas@zadara.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/md.c | 54 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 44 insertions(+), 10 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 6b074c2202d5..3cc28b283607 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1034,6 +1034,7 @@ struct super_type  {
 					  struct md_rdev *refdev,
 					  int minor_version);
 	int		    (*validate_super)(struct mddev *mddev,
+					      struct md_rdev *freshest,
 					      struct md_rdev *rdev);
 	void		    (*sync_super)(struct mddev *mddev,
 					  struct md_rdev *rdev);
@@ -1160,8 +1161,9 @@ static int super_90_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor
 
 /*
  * validate_super for 0.90.0
+ * note: we are not using "freshest" for 0.9 superblock
  */
-static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
+static int super_90_validate(struct mddev *mddev, struct md_rdev *freshest, struct md_rdev *rdev)
 {
 	mdp_disk_t *desc;
 	mdp_super_t *sb = page_address(rdev->sb_page);
@@ -1665,7 +1667,7 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
 	return ret;
 }
 
-static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
+static int super_1_validate(struct mddev *mddev, struct md_rdev *freshest, struct md_rdev *rdev)
 {
 	struct mdp_superblock_1 *sb = page_address(rdev->sb_page);
 	__u64 ev1 = le64_to_cpu(sb->events);
@@ -1761,13 +1763,15 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
 		}
 	} else if (mddev->pers == NULL) {
 		/* Insist of good event counter while assembling, except for
-		 * spares (which don't need an event count) */
-		++ev1;
+		 * spares (which don't need an event count).
+		 * Similar to mdadm, we allow event counter difference of 1
+		 * from the freshest device.
+		 */
 		if (rdev->desc_nr >= 0 &&
 		    rdev->desc_nr < le32_to_cpu(sb->max_dev) &&
 		    (le16_to_cpu(sb->dev_roles[rdev->desc_nr]) < MD_DISK_ROLE_MAX ||
 		     le16_to_cpu(sb->dev_roles[rdev->desc_nr]) == MD_DISK_ROLE_JOURNAL))
-			if (ev1 < mddev->events)
+			if (ev1 + 1 < mddev->events)
 				return -EINVAL;
 	} else if (mddev->bitmap) {
 		/* If adding to array with a bitmap, then we can accept an
@@ -1788,8 +1792,38 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
 		    rdev->desc_nr >= le32_to_cpu(sb->max_dev)) {
 			role = MD_DISK_ROLE_SPARE;
 			rdev->desc_nr = -1;
-		} else
+		} else if (mddev->pers == NULL && freshest && ev1 < mddev->events) {
+			/*
+			 * If we are assembling, and our event counter is smaller than the
+			 * highest event counter, we cannot trust our superblock about the role.
+			 * It could happen that our rdev was marked as Faulty, and all other
+			 * superblocks were updated with +1 event counter.
+			 * Then, before the next superblock update, which typically happens when
+			 * remove_and_add_spares() removes the device from the array, there was
+			 * a crash or reboot.
+			 * If we allow current rdev without consulting the freshest superblock,
+			 * we could cause data corruption.
+			 * Note that in this case our event counter is smaller by 1 than the
+			 * highest, otherwise, this rdev would not be allowed into array;
+			 * both kernel and mdadm allow event counter difference of 1.
+			 */
+			struct mdp_superblock_1 *freshest_sb = page_address(freshest->sb_page);
+			u32 freshest_max_dev = le32_to_cpu(freshest_sb->max_dev);
+
+			if (rdev->desc_nr >= freshest_max_dev) {
+				/* this is unexpected, better not proceed */
+				pr_warn("md: %s: rdev[%pg]: desc_nr(%d) >= freshest(%pg)->sb->max_dev(%u)\n",
+						mdname(mddev), rdev->bdev, rdev->desc_nr,
+						freshest->bdev, freshest_max_dev);
+				return -EUCLEAN;
+			}
+
+			role = le16_to_cpu(freshest_sb->dev_roles[rdev->desc_nr]);
+			pr_debug("md: %s: rdev[%pg]: role=%d(0x%x) according to freshest %pg\n",
+				     mdname(mddev), rdev->bdev, role, role, freshest->bdev);
+		} else {
 			role = le16_to_cpu(sb->dev_roles[rdev->desc_nr]);
+		}
 		switch(role) {
 		case MD_DISK_ROLE_SPARE: /* spare */
 			break;
@@ -2691,7 +2725,7 @@ static int add_bound_rdev(struct md_rdev *rdev)
 		 * and should be added immediately.
 		 */
 		super_types[mddev->major_version].
-			validate_super(mddev, rdev);
+			validate_super(mddev, NULL/*freshest*/, rdev);
 		if (add_journal)
 			mddev_suspend(mddev);
 		err = mddev->pers->hot_add_disk(mddev, rdev);
@@ -3593,7 +3627,7 @@ static void analyze_sbs(struct mddev *mddev)
 		}
 
 	super_types[mddev->major_version].
-		validate_super(mddev, freshest);
+		validate_super(mddev, NULL/*freshest*/, freshest);
 
 	i = 0;
 	rdev_for_each_safe(rdev, tmp, mddev) {
@@ -3608,7 +3642,7 @@ static void analyze_sbs(struct mddev *mddev)
 		}
 		if (rdev != freshest) {
 			if (super_types[mddev->major_version].
-			    validate_super(mddev, rdev)) {
+			    validate_super(mddev, freshest, rdev)) {
 				pr_warn("md: kicking non-fresh %s from array!\n",
 					bdevname(rdev->bdev,b));
 				md_kick_rdev_from_array(rdev);
@@ -6453,7 +6487,7 @@ static int add_new_disk(struct mddev *mddev, mdu_disk_info_t *info)
 			rdev->saved_raid_disk = rdev->raid_disk;
 		} else
 			super_types[mddev->major_version].
-				validate_super(mddev, rdev);
+				validate_super(mddev, NULL/*freshest*/, rdev);
 		if ((info->state & (1<<MD_DISK_SYNC)) &&
 		     rdev->raid_disk != info->raid_disk) {
 			/* This was a hot-add request, but events doesn't
-- 
2.43.0