[PATCH 6.7 112/713] md: remove flag RemoveSynchronized

Sasha Levin
2024-03-24T22:49:11Z

From: Yu Kuai <yukuai3@huawei.com>

[ Upstream commit c891f1fd90e66e584bb1353e1859cef7c9eb36f8 ]

rcu is not used correctly here, because synchronize_rcu() is called
before replacing old value, for example:

remove_and_add_spares // other path
synchronize_rcu
// called before replacing old value
set_bit(RemoveSynchronized)
rcu_read_lock()
rdev = conf->mirros[].rdev
pers->hot_remove_disk
conf->mirros[].rdev = NULL;
if (!test_bit(RemoveSynchronized))
synchronize_rcu
/*
* won't be called, and won't wait
* for concurrent readers to be done.
*/
// access rdev after remove_and_add_spares()
rcu_read_unlock()

Fortunately, there is a separate rcu protection to prevent such rdev
to be freed:

md_kick_rdev_from_array //other path
rcu_read_lock()
rdev = conf->mirros[].rdev
list_del_rcu(&rdev->same_set)

rcu_read_unlock()
/*
* rdev can be removed from conf, but
* rdev won't be freed.
*/
synchronize_rcu()
free rdev

Hence remove this useless flag and prepare to remove rcu protection to
access rdev from 'conf'.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231125081604.3939938-2-yukuai1@huaweicloud.com
Stable-dep-of: 257ac239ffcf ("md/raid1: fix choose next idle in read_balance()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/md/md-multipath.c | 9 ---------
drivers/md/md.c | 37 ++++++-------------------------------
drivers/md/md.h | 5 -----
drivers/md/raid1.c | 9 ---------
drivers/md/raid10.c | 9 ---------
drivers/md/raid5.c | 9 ---------
6 files changed, 6 insertions(+), 72 deletions(-)

diff --git a/drivers/md/md-multipath.c b/drivers/md/md-multipath.c
index d22276870283d..aa77133f31887 100644
--- a/drivers/md/md-multipath.c
+++ b/drivers/md/md-multipath.c
@@ -258,15 +258,6 @@ static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
goto abort;
}
p->rdev = NULL;
- if (!test_bit(RemoveSynchronized, &rdev->flags)) {
- synchronize_rcu();
- if (atomic_read(&rdev->nr_pending)) {
- /* lost the race, try later */
- err = -EBUSY;
- p->rdev = rdev;
- goto abort;
- }
- }
err = md_integrity_register(mddev);
}
abort:
diff --git a/drivers/md/md.c b/drivers/md/md.c
index b2f27ac51bfb6..99b60d37114c4 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -9314,44 +9314,19 @@ static int remove_and_add_spares(struct mddev *mddev,
struct md_rdev *rdev;
int spares = 0;
int removed = 0;
- bool remove_some = false;

if (this && test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
/* Mustn't remove devices when resync thread is running */
return 0;

rdev_for_each(rdev, mddev) {
- if ((this == NULL || rdev == this) &&
- rdev->raid_disk >= 0 &&
- !test_bit(Blocked, &rdev->flags) &&
- test_bit(Faulty, &rdev->flags) &&
- atomic_read(&rdev->nr_pending)==0) {
- /* Faulty non-Blocked devices with nr_pending == 0
- * never get nr_pending incremented,
- * never get Faulty cleared, and never get Blocked set.
- * So we can synchronize_rcu now rather than once per device
- */
- remove_some = true;
- set_bit(RemoveSynchronized, &rdev->flags);
- }
- }
-
- if (remove_some)
- synchronize_rcu();
- rdev_for_each(rdev, mddev) {
- if ((this == NULL || rdev == this) &&
- (test_bit(RemoveSynchronized, &rdev->flags) ||
- rdev_removeable(rdev))) {
- if (mddev->pers->hot_remove_disk(
- mddev, rdev) == 0) {
- sysfs_unlink_rdev(mddev, rdev);
- rdev->saved_raid_disk = rdev->raid_disk;
- rdev->raid_disk = -1;
- removed++;
- }
+ if ((this == NULL || rdev == this) && rdev_removeable(rdev) &&
+ !mddev->pers->hot_remove_disk(mddev, rdev)) {
+ sysfs_unlink_rdev(mddev, rdev);
+ rdev->saved_raid_disk = rdev->raid_disk;
+ rdev->raid_disk = -1;
+ removed++;
}
- if (remove_some && test_bit(RemoveSynchronized, &rdev->flags))
- clear_bit(RemoveSynchronized, &rdev->flags);
}

if (removed && mddev->kobj.sd)
diff --git a/drivers/md/md.h b/drivers/md/md.h
index ade83af123a22..8d881cc597992 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -190,11 +190,6 @@ enum flag_bits {
* than other devices in the array
*/
ClusterRemove,
- RemoveSynchronized, /* synchronize_rcu() was called after
- * this device was known to be faulty,
- * so it is safe to remove without
- * another synchronize_rcu() call.
- */
ExternalBbl, /* External metadata provides bad
* block management for a disk
*/
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index e138922d51292..6bd42ccbea9c4 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1863,15 +1863,6 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
goto abort;
}
p->rdev = NULL;
- if (!test_bit(RemoveSynchronized, &rdev->flags)) {
- synchronize_rcu();
- if (atomic_read(&rdev->nr_pending)) {
- /* lost the race, try later */
- err = -EBUSY;
- p->rdev = rdev;
- goto abort;
- }
- }
if (conf->mirrors[conf->raid_disks + number].rdev) {
/* We just removed a device that is being replaced.
* Move down the replacement. We drain all IO before
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index b7b0a573e7f8b..6e828a6aa0b0a 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2247,15 +2247,6 @@ static int raid10_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
goto abort;
}
*rdevp = NULL;
- if (!test_bit(RemoveSynchronized, &rdev->flags)) {
- synchronize_rcu();
- if (atomic_read(&rdev->nr_pending)) {
- /* lost the race, try later */
- err = -EBUSY;
- *rdevp = rdev;
- goto abort;
- }
- }
if (p->replacement) {
/* We must have just cleared 'rdev' */
p->rdev = p->replacement;
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 6fe334bb954ab..f03e4231bec11 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -8241,15 +8241,6 @@ static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
goto abort;
}
*rdevp = NULL;
- if (!test_bit(RemoveSynchronized, &rdev->flags)) {
- lockdep_assert_held(&mddev->reconfig_mutex);
- synchronize_rcu();
- if (atomic_read(&rdev->nr_pending)) {
- /* lost the race, try later */
- err = -EBUSY;
- rcu_assign_pointer(*rdevp, rdev);
- }
- }
if (!err) {
err = log_modify(conf, rdev, false);
if (err)
--
2.43.0