Re: [PATCH -next v2 2/6] md: remove flag RemoveSynchronized
From: Yu Kuai
Date: Fri Nov 24 2023 - 04:13:12 EST
Hi,
在 2023/11/24 16:28, Song Liu 写道:
On Fri, Oct 20, 2023 at 7:25 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
From: Yu Kuai <yukuai3@xxxxxxxxxx>
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@xxxxxxxxxx>
RemoveSynchronized is not removed from md.h.
Yes, thanks for the notice.
Kuai
---
drivers/md/md-multipath.c | 9 ---------
drivers/md/md.c | 37 ++++++-------------------------------
drivers/md/raid1.c | 9 ---------
drivers/md/raid10.c | 9 ---------
drivers/md/raid5.c | 9 ---------
5 files changed, 6 insertions(+), 67 deletions(-)
diff --git a/drivers/md/md-multipath.c b/drivers/md/md-multipath.c
index d22276870283..aa77133f3188 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 09686d8db983..68f3bb6e89cb 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -9250,44 +9250,19 @@ 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/raid1.c b/drivers/md/raid1.c
index c13088eae401..4348d670439d 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1836,15 +1836,6 @@ 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 4b5f34f320c8..33ab00323cae 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2219,15 +2219,6 @@ 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 27a4dce51c92..a80be51b4825 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -8202,15 +8202,6 @@ 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)
--
2.39.2
.