[md PATCH 05/18] md/raid10: add rcu protection to rdev access in raid10_sync_request.

NeilBrown
2016-06-02T06:19:52Z

mirrors[].rdev can become NULL at any point unless:
- a counted reference is held
- ->reconfig_mutex is held, or
- rcu_read_lock() is held

Previously they could not become NULL during a resync/recovery/reshape either.
However when remove_and_add_spares() was added to hot_remove_disk(), that
changed.

So raid10_sync_request didn't previously need to protect rdev access,
but now it does.

Signed-off-by: NeilBrown <neilb@suse.com>
---
drivers/md/raid10.c | 120 +++++++++++++++++++++++++++++++--------------------
1 file changed, 72 insertions(+), 48 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index e6f3a11f8f70..f6f21a253926 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2871,11 +2871,14 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
/* Completed a full sync so the replacements
* are now fully recovered.
*/
- for (i = 0; i < conf->geo.raid_disks; i++)
- if (conf->mirrors[i].replacement)
- conf->mirrors[i].replacement
- ->recovery_offset
- = MaxSector;
+ rcu_read_lock();
+ for (i = 0; i < conf->geo.raid_disks; i++) {
+ struct md_rdev *rdev =
+ rcu_dereference(conf->mirrors[i].replacement);
+ if (rdev)
+ rdev->recovery_offset = MaxSector;
+ }
+ rcu_read_unlock();
}
conf->fullsync = 0;
}
@@ -2934,14 +2937,17 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
int must_sync;
int any_working;
struct raid10_info *mirror = &conf->mirrors[i];
+ struct md_rdev *mrdev, *mreplace;

- if ((mirror->rdev == NULL ||
- test_bit(In_sync, &mirror->rdev->flags))
- &&
- (mirror->replacement == NULL ||
- test_bit(Faulty,
- &mirror->replacement->flags)))
+ rcu_read_lock();
+ mrdev = rcu_dereference(mirror->rdev);
+ mreplace = rcu_dereference(mirror->replacement);
+
+ if ((mrdev == NULL ||
+ test_bit(In_sync, &mrdev->flags))) {
+ rcu_read_unlock();
continue;
+ }

still_degraded = 0;
/* want to reconstruct this device */
@@ -2951,6 +2957,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
/* last stripe is not complete - don't
* try to recover this sector.
*/
+ rcu_read_unlock();
continue;
}
/* Unless we are doing a full sync, or a replacement
@@ -2962,14 +2969,19 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
if (sync_blocks < max_sync)
max_sync = sync_blocks;
if (!must_sync &&
- mirror->replacement == NULL &&
+ mreplace == NULL &&
!conf->fullsync) {
/* yep, skip the sync_blocks here, but don't assume
* that there will never be anything to do here
*/
chunks_skipped = -1;
+ rcu_read_unlock();
continue;
}
+ atomic_inc(&mrdev->nr_pending);
+ if (mreplace)
+ atomic_inc(&mreplace->nr_pending);
+ rcu_read_unlock();

r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
r10_bio->state = 0;
@@ -2988,12 +3000,15 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
/* Need to check if the array will still be
* degraded
*/
- for (j = 0; j < conf->geo.raid_disks; j++)
- if (conf->mirrors[j].rdev == NULL ||
- test_bit(Faulty, &conf->mirrors[j].rdev->flags)) {
+ rcu_read_lock();
+ for (j = 0; j < conf->geo.raid_disks; j++) {
+ struct md_rdev *rdev = rcu_dereference(
+ conf->mirrors[j].rdev);
+ if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
still_degraded = 1;
break;
}
+ }

must_sync = bitmap_start_sync(mddev->bitmap, sect,
&sync_blocks, still_degraded);
@@ -3003,15 +3018,15 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
int k;
int d = r10_bio->devs[j].devnum;
sector_t from_addr, to_addr;
- struct md_rdev *rdev;
+ struct md_rdev *rdev =
+ rcu_dereference(conf->mirrors[d].rdev);
sector_t sector, first_bad;
int bad_sectors;
- if (!conf->mirrors[d].rdev ||
- !test_bit(In_sync, &conf->mirrors[d].rdev->flags))
+ if (!rdev ||
+ !test_bit(In_sync, &rdev->flags))
continue;
/* This is where we read from */
any_working = 1;
- rdev = conf->mirrors[d].rdev;
sector = r10_bio->devs[j].addr;

if (is_badblock(rdev, sector, max_sync,
@@ -3050,8 +3065,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
r10_bio->devs[1].devnum = i;
r10_bio->devs[1].addr = to_addr;

- rdev = mirror->rdev;
- if (!test_bit(In_sync, &rdev->flags)) {
+ if (!test_bit(In_sync, &mrdev->flags)) {
bio = r10_bio->devs[1].bio;
bio_reset(bio);
bio->bi_next = biolist;
@@ -3060,8 +3074,8 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
bio->bi_end_io = end_sync_write;
bio->bi_rw = WRITE;
bio->bi_iter.bi_sector = to_addr
- + rdev->data_offset;
- bio->bi_bdev = rdev->bdev;
+ + mrdev->data_offset;
+ bio->bi_bdev = mrdev->bdev;
atomic_inc(&r10_bio->remaining);
} else
r10_bio->devs[1].bio->bi_end_io = NULL;
@@ -3070,8 +3084,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
bio = r10_bio->devs[1].repl_bio;
if (bio)
bio->bi_end_io = NULL;
- rdev = mirror->replacement;
- /* Note: if rdev != NULL, then bio
+ /* Note: if mreplace != NULL, then bio
* cannot be NULL as r10buf_pool_alloc will
* have allocated it.
* So the second test here is pointless.
@@ -3079,8 +3092,8 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
* this comment keeps human reviewers
* happy.
*/
- if (rdev == NULL || bio == NULL ||
- test_bit(Faulty, &rdev->flags))
+ if (mreplace == NULL || bio == NULL ||
+ test_bit(Faulty, &mreplace->flags))
break;
bio_reset(bio);
bio->bi_next = biolist;
@@ -3089,11 +3102,12 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
bio->bi_end_io = end_sync_write;
bio->bi_rw = WRITE;
bio->bi_iter.bi_sector = to_addr +
- rdev->data_offset;
- bio->bi_bdev = rdev->bdev;
+ mreplace->data_offset;
+ bio->bi_bdev = mreplace->bdev;
atomic_inc(&r10_bio->remaining);
break;
}
+ rcu_read_unlock();
if (j == conf->copies) {
/* Cannot recover, so abort the recovery or
* record a bad block */
@@ -3106,15 +3120,15 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
if (r10_bio->devs[k].devnum == i)
break;
if (!test_bit(In_sync,
- &mirror->rdev->flags)
+ &mrdev->flags)
&& !rdev_set_badblocks(
- mirror->rdev,
+ mrdev,
r10_bio->devs[k].addr,
max_sync, 0))
any_working = 0;
- if (mirror->replacement &&
+ if (mreplace &&
!rdev_set_badblocks(
- mirror->replacement,
+ mreplace,
r10_bio->devs[k].addr,
max_sync, 0))
any_working = 0;
@@ -3132,8 +3146,14 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
if (rb2)
atomic_dec(&rb2->remaining);
r10_bio = rb2;
+ rdev_dec_pending(mrdev, mddev);
+ if (mreplace)
+ rdev_dec_pending(mreplace, mddev);
break;
}
+ rdev_dec_pending(mrdev, mddev);
+ if (mreplace)
+ rdev_dec_pending(mreplace, mddev);
}
if (biolist == NULL) {
while (r10_bio) {
@@ -3178,6 +3198,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
int d = r10_bio->devs[i].devnum;
sector_t first_bad, sector;
int bad_sectors;
+ struct md_rdev *rdev;

if (r10_bio->devs[i].repl_bio)
r10_bio->devs[i].repl_bio->bi_end_io = NULL;
@@ -3185,12 +3206,14 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
bio = r10_bio->devs[i].bio;
bio_reset(bio);
bio->bi_error = -EIO;
- if (conf->mirrors[d].rdev == NULL ||
- test_bit(Faulty, &conf->mirrors[d].rdev->flags))
+ rcu_read_lock();
+ rdev = rcu_dereference(conf->mirrors[d].rdev);
+ if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
+ rcu_read_unlock();
continue;
+ }
sector = r10_bio->devs[i].addr;
- if (is_badblock(conf->mirrors[d].rdev,
- sector, max_sync,
+ if (is_badblock(rdev, sector, max_sync,
&first_bad, &bad_sectors)) {
if (first_bad > sector)
max_sync = first_bad - sector;
@@ -3198,25 +3221,28 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
bad_sectors -= (sector - first_bad);
if (max_sync > bad_sectors)
max_sync = bad_sectors;
+ rcu_read_unlock();
continue;
}
}
- atomic_inc(&conf->mirrors[d].rdev->nr_pending);
+ atomic_inc(&rdev->nr_pending);
atomic_inc(&r10_bio->remaining);
bio->bi_next = biolist;
biolist = bio;
bio->bi_private = r10_bio;
bio->bi_end_io = end_sync_read;
bio->bi_rw = READ;
- bio->bi_iter.bi_sector = sector +
- conf->mirrors[d].rdev->data_offset;
- bio->bi_bdev = conf->mirrors[d].rdev->bdev;
+ bio->bi_iter.bi_sector = sector + rdev->data_offset;
+ bio->bi_bdev = rdev->bdev;
count++;

- if (conf->mirrors[d].replacement == NULL ||
- test_bit(Faulty,
- &conf->mirrors[d].replacement->flags))
+ rdev = rcu_dereference(conf->mirrors[d].replacement);
+ if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
+ rcu_read_unlock();
continue;
+ }
+ atomic_inc(&rdev->nr_pending);
+ rcu_read_unlock();

/* Need to set up for writing to the replacement */
bio = r10_bio->devs[i].repl_bio;
@@ -3224,15 +3250,13 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
bio->bi_error = -EIO;

sector = r10_bio->devs[i].addr;
- atomic_inc(&conf->mirrors[d].replacement->nr_pending);
bio->bi_next = biolist;
biolist = bio;
bio->bi_private = r10_bio;
bio->bi_end_io = end_sync_write;
bio->bi_rw = WRITE;
- bio->bi_iter.bi_sector = sector +
- conf->mirrors[d].replacement->data_offset;
- bio->bi_bdev = conf->mirrors[d].replacement->bdev;
+ bio->bi_iter.bi_sector = sector + rdev->data_offset;
+ bio->bi_bdev = rdev->bdev;
count++;
}