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Message-ID: <fb6a482a-a546-3e6b-0a0a-238f81b0bb23@huaweicloud.com>
Date: Fri, 24 Nov 2023 17:13:03 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Song Liu <song@...nel.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
yi.zhang@...wei.com, yangerkun@...wei.com,
"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next v2 2/6] md: remove flag RemoveSynchronized
Hi,
在 2023/11/24 16:28, Song Liu 写道:
> On Fri, Oct 20, 2023 at 7:25 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>>
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> 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@...wei.com>
>
> 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
>>
>
> .
>
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