[PATCH AUTOSEL 6.7 081/108] md: Whenassemble the array, consult the superblock of the freshest device

Sasha Levin
2024-01-16T19:46:10Z

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 9bdd57324c37..da33270971ab 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1209,6 +1209,7 @@ 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);
@@ -1346,8 +1347,9 @@ 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);
@@ -1859,7 +1861,7 @@ 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);
@@ -1955,13 +1957,15 @@ 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
@@ -1982,8 +1986,38 @@ 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;
@@ -2890,7 +2924,7 @@ 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);
err = mddev->pers->hot_add_disk(mddev, rdev);
if (err) {
md_kick_rdev_from_array(rdev);
@@ -3827,7 +3861,7 @@ static int 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) {
@@ -3842,7 +3876,7 @@ static int 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 %pg from array!\n",
rdev->bdev);
md_kick_rdev_from_array(rdev);
@@ -6833,7 +6867,7 @@ int md_add_new_disk(struct mddev *mddev, struct mdu_disk_info_s *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