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Merge branch 'md-next-rcu-cleanup' into md-next
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From Yu Kuai:

md: remove rcu protection to access rdev from conf

The lifetime of rdev:

1. md_import_device() generate a rdev based on underlying disk;

   mddev_lock()
   rdev = kzalloc();
   rdev->bdev = blkdev_get_by_dev();
   mddev_unlock()

2. bind_rdev_to_array() add this rdev to mddev->disks;

   mddev_lock()
   kobject_add(&rdev->kobj, &mddev->kobj, ...);
   list_add_rcu(&rdev->same_set, &mddev->disks);
   mddev_unlock()

3. remove_and_add_spares() add this rdev to conf;

   mddev_lock()
   rdev_addable();
   pers->hot_add_disk();
   rcu_assign_pointer(conf->rdev, rdev);
   mddev_unlock()

4. Use this array with rdev;

5. remove_and_add_spares() remove rdev from conf;

   // triggered by sysfs/ioctl
   mddev_lock()
   rdev_removeable();
   pers->hot_remove_disk();
    rcu_assign_pointer(conf->rdev, NULL);
    synchronize_rcu();
   mddev_unlock()

   // triggered by daemon
   mddev_lock()
   rdev_removeable();
   synchronize_rcu(); -> this can't protect accessing rdev from conf
   pers->hot_remove_disk();
    rcu_assign_pointer(conf->rdev, NULL);
   mddev_unlock()

6. md_kick_rdev_from_array() remove rdev from mddev->disks;

   mddev_lock()
   list_del_rcu(&rdev->same_set);
   synchronize_rcu();
   list_add(&rdev->same_set, &mddev->deleting)
   mddev_unlock()
    export_rdev

There are two separate rcu protection for rdev, and this pathset remove
the protection of conf(step 3 and 5), because it's safe to access rdev
from conf in following cases:

 - If 'reconfig_mutex' is held, because rdev can't be added or rmoved to
 conf;
 - If there is normal IO inflight, because mddev_suspend() will wait for
 IO to be done and prevent rdev to be added or removed to conf;
 - If sync thread is running, because remove_and_add_spares() can only be
 called from daemon thread when sync thread is done, and
 'MD_RECOVERY_RUNNING' is also checked for ioctl/sysfs;
 - if any spinlock or rcu_read_lock() is held, because synchronize_rcu()
 from step 6 prevent rdev to be freed until spinlock is released or
 rcu_read_unlock();
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Song Liu committed Nov 28, 2023
2 parents bed9e27 + 7ecab28 commit 726a9b6
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Showing 9 changed files with 168 additions and 421 deletions.
32 changes: 12 additions & 20 deletions drivers/md/md-multipath.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -32,17 +32,15 @@ static int multipath_map (struct mpconf *conf)
* now we use the first available disk.
*/

rcu_read_lock();
for (i = 0; i < disks; i++) {
struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
struct md_rdev *rdev = conf->multipaths[i].rdev;

if (rdev && test_bit(In_sync, &rdev->flags) &&
!test_bit(Faulty, &rdev->flags)) {
atomic_inc(&rdev->nr_pending);
rcu_read_unlock();
return i;
}
}
rcu_read_unlock();

pr_crit_ratelimited("multipath_map(): no more operational IO paths?\n");
return (-1);
Expand Down Expand Up @@ -137,14 +135,16 @@ static void multipath_status(struct seq_file *seq, struct mddev *mddev)
struct mpconf *conf = mddev->private;
int i;

lockdep_assert_held(&mddev->lock);

seq_printf (seq, " [%d/%d] [", conf->raid_disks,
conf->raid_disks - mddev->degraded);
rcu_read_lock();
for (i = 0; i < conf->raid_disks; i++) {
struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
seq_printf (seq, "%s", rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
struct md_rdev *rdev = READ_ONCE(conf->multipaths[i].rdev);

seq_printf(seq, "%s",
rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
}
rcu_read_unlock();
seq_putc(seq, ']');
}

Expand Down Expand Up @@ -182,7 +182,7 @@ static void multipath_error (struct mddev *mddev, struct md_rdev *rdev)
conf->raid_disks - mddev->degraded);
}

static void print_multipath_conf (struct mpconf *conf)
static void print_multipath_conf(struct mpconf *conf)
{
int i;
struct multipath_info *tmp;
Expand All @@ -195,6 +195,7 @@ static void print_multipath_conf (struct mpconf *conf)
pr_debug(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
conf->raid_disks);

lockdep_assert_held(&conf->mddev->reconfig_mutex);
for (i = 0; i < conf->raid_disks; i++) {
tmp = conf->multipaths + i;
if (tmp->rdev)
Expand Down Expand Up @@ -231,7 +232,7 @@ static int multipath_add_disk(struct mddev *mddev, struct md_rdev *rdev)
rdev->raid_disk = path;
set_bit(In_sync, &rdev->flags);
spin_unlock_irq(&conf->device_lock);
rcu_assign_pointer(p->rdev, rdev);
WRITE_ONCE(p->rdev, rdev);
err = 0;
break;
}
Expand All @@ -257,16 +258,7 @@ static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
err = -EBUSY;
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;
}
}
WRITE_ONCE(p->rdev, NULL);
err = md_integrity_register(mddev);
}
abort:
Expand Down
37 changes: 6 additions & 31 deletions drivers/md/md.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -9244,44 +9244,19 @@ 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)
Expand Down
5 changes: 0 additions & 5 deletions drivers/md/md.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
*/
Expand Down
71 changes: 23 additions & 48 deletions drivers/md/raid1.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -609,7 +609,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
int choose_first;
int choose_next_idle;

rcu_read_lock();
/*
* Check if we can balance. We can balance on the whole
* device if no resync is going on, or below the resync window.
Expand Down Expand Up @@ -642,7 +641,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
unsigned int pending;
bool nonrot;

rdev = rcu_dereference(conf->mirrors[disk].rdev);
rdev = conf->mirrors[disk].rdev;
if (r1_bio->bios[disk] == IO_BLOCKED
|| rdev == NULL
|| test_bit(Faulty, &rdev->flags))
Expand Down Expand Up @@ -773,7 +772,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
}

if (best_disk >= 0) {
rdev = rcu_dereference(conf->mirrors[best_disk].rdev);
rdev = conf->mirrors[best_disk].rdev;
if (!rdev)
goto retry;
atomic_inc(&rdev->nr_pending);
Expand All @@ -784,7 +783,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect

conf->mirrors[best_disk].next_seq_sect = this_sector + sectors;
}
rcu_read_unlock();
*max_sectors = sectors;

return best_disk;
Expand Down Expand Up @@ -1235,14 +1233,12 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,

if (r1bio_existed) {
/* Need to get the block device name carefully */
struct md_rdev *rdev;
rcu_read_lock();
rdev = rcu_dereference(conf->mirrors[r1_bio->read_disk].rdev);
struct md_rdev *rdev = conf->mirrors[r1_bio->read_disk].rdev;

if (rdev)
snprintf(b, sizeof(b), "%pg", rdev->bdev);
else
strcpy(b, "???");
rcu_read_unlock();
}

/*
Expand Down Expand Up @@ -1396,10 +1392,9 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,

disks = conf->raid_disks * 2;
blocked_rdev = NULL;
rcu_read_lock();
max_sectors = r1_bio->sectors;
for (i = 0; i < disks; i++) {
struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
struct md_rdev *rdev = conf->mirrors[i].rdev;

/*
* The write-behind io is only attempted on drives marked as
Expand Down Expand Up @@ -1465,7 +1460,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
}
r1_bio->bios[i] = bio;
}
rcu_read_unlock();

if (unlikely(blocked_rdev)) {
/* Wait for this device to become unblocked */
Expand Down Expand Up @@ -1617,15 +1611,16 @@ static void raid1_status(struct seq_file *seq, struct mddev *mddev)
struct r1conf *conf = mddev->private;
int i;

lockdep_assert_held(&mddev->lock);

seq_printf(seq, " [%d/%d] [", conf->raid_disks,
conf->raid_disks - mddev->degraded);
rcu_read_lock();
for (i = 0; i < conf->raid_disks; i++) {
struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
struct md_rdev *rdev = READ_ONCE(conf->mirrors[i].rdev);

seq_printf(seq, "%s",
rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
}
rcu_read_unlock();
seq_printf(seq, "]");
}

Expand Down Expand Up @@ -1691,16 +1686,15 @@ static void print_conf(struct r1conf *conf)
pr_debug(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
conf->raid_disks);

rcu_read_lock();
lockdep_assert_held(&conf->mddev->reconfig_mutex);
for (i = 0; i < conf->raid_disks; i++) {
struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
struct md_rdev *rdev = conf->mirrors[i].rdev;
if (rdev)
pr_debug(" disk %d, wo:%d, o:%d, dev:%pg\n",
i, !test_bit(In_sync, &rdev->flags),
!test_bit(Faulty, &rdev->flags),
rdev->bdev);
}
rcu_read_unlock();
}

static void close_sync(struct r1conf *conf)
Expand Down Expand Up @@ -1810,7 +1804,7 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
*/
if (rdev->saved_raid_disk < 0)
conf->fullsync = 1;
rcu_assign_pointer(p->rdev, rdev);
WRITE_ONCE(p->rdev, rdev);
break;
}
if (test_bit(WantReplacement, &p->rdev->flags) &&
Expand All @@ -1826,7 +1820,7 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
rdev->raid_disk = repl_slot;
err = 0;
conf->fullsync = 1;
rcu_assign_pointer(p[conf->raid_disks].rdev, rdev);
WRITE_ONCE(p[conf->raid_disks].rdev, rdev);
}

print_conf(conf);
Expand Down Expand Up @@ -1862,16 +1856,7 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
err = -EBUSY;
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;
}
}
WRITE_ONCE(p->rdev, NULL);
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
Expand All @@ -1892,7 +1877,7 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
goto abort;
}
clear_bit(Replacement, &repl->flags);
p->rdev = repl;
WRITE_ONCE(p->rdev, repl);
conf->mirrors[conf->raid_disks + number].rdev = NULL;
unfreeze_array(conf);
}
Expand Down Expand Up @@ -2290,24 +2275,22 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
sector_t first_bad;
int bad_sectors;

rcu_read_lock();
rdev = rcu_dereference(conf->mirrors[d].rdev);
rdev = conf->mirrors[d].rdev;
if (rdev &&
(test_bit(In_sync, &rdev->flags) ||
(!test_bit(Faulty, &rdev->flags) &&
rdev->recovery_offset >= sect + s)) &&
is_badblock(rdev, sect, s,
&first_bad, &bad_sectors) == 0) {
atomic_inc(&rdev->nr_pending);
rcu_read_unlock();
if (sync_page_io(rdev, sect, s<<9,
conf->tmppage, REQ_OP_READ, false))
success = 1;
rdev_dec_pending(rdev, mddev);
if (success)
break;
} else
rcu_read_unlock();
}

d++;
if (d == conf->raid_disks * 2)
d = 0;
Expand All @@ -2326,29 +2309,24 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
if (d==0)
d = conf->raid_disks * 2;
d--;
rcu_read_lock();
rdev = rcu_dereference(conf->mirrors[d].rdev);
rdev = conf->mirrors[d].rdev;
if (rdev &&
!test_bit(Faulty, &rdev->flags)) {
atomic_inc(&rdev->nr_pending);
rcu_read_unlock();
r1_sync_page_io(rdev, sect, s,
conf->tmppage, WRITE);
rdev_dec_pending(rdev, mddev);
} else
rcu_read_unlock();
}
}
d = start;
while (d != read_disk) {
if (d==0)
d = conf->raid_disks * 2;
d--;
rcu_read_lock();
rdev = rcu_dereference(conf->mirrors[d].rdev);
rdev = conf->mirrors[d].rdev;
if (rdev &&
!test_bit(Faulty, &rdev->flags)) {
atomic_inc(&rdev->nr_pending);
rcu_read_unlock();
if (r1_sync_page_io(rdev, sect, s,
conf->tmppage, READ)) {
atomic_add(s, &rdev->corrected_errors);
Expand All @@ -2359,8 +2337,7 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
rdev->bdev);
}
rdev_dec_pending(rdev, mddev);
} else
rcu_read_unlock();
}
}
sectors -= s;
sect += s;
Expand Down Expand Up @@ -2741,7 +2718,6 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,

r1_bio = raid1_alloc_init_r1buf(conf);

rcu_read_lock();
/*
* If we get a correctably read error during resync or recovery,
* we might want to read from a different device. So we
Expand All @@ -2762,7 +2738,7 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
struct md_rdev *rdev;
bio = r1_bio->bios[i];

rdev = rcu_dereference(conf->mirrors[i].rdev);
rdev = conf->mirrors[i].rdev;
if (rdev == NULL ||
test_bit(Faulty, &rdev->flags)) {
if (i < conf->raid_disks)
Expand Down Expand Up @@ -2820,7 +2796,6 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
bio->bi_opf |= MD_FAILFAST;
}
}
rcu_read_unlock();
if (disk < 0)
disk = wonly;
r1_bio->read_disk = disk;
Expand Down
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