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.
> ---
> 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
>
