[md PATCH 12/18] md/raid1: add rcu protection to rdev in fix_read_error

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

Since remove_and_add_spares() was added to hot_remove_disk() it has
been possible for an rdev to be hot-removed while fix_read_error()
was running, so we need to be more careful, and take a reference to
the rdev while performing IO.

Signed-off-by: NeilBrown <neilb@suse.com>
---
drivers/md/raid1.c | 52 ++++++++++++++++++++++++++++++++--------------------
1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index cc53120e4d68..0ee901ccc9c5 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2056,29 +2056,30 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
s = PAGE_SIZE >> 9;

do {
- /* Note: no rcu protection needed here
- * as this is synchronous in the raid1d thread
- * which is the thread that might remove
- * a device. If raid1d ever becomes multi-threaded....
- */
sector_t first_bad;
int bad_sectors;

- rdev = conf->mirrors[d].rdev;
+ rcu_read_lock();
+ rdev = rcu_dereference(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 &&
- sync_page_io(rdev, sect, s<<9,
- conf->tmppage, READ, false))
- success = 1;
- else {
- d++;
- if (d == conf->raid_disks * 2)
- d = 0;
- }
+ &first_bad, &bad_sectors) == 0) {
+ atomic_inc(&rdev->nr_pending);
+ rcu_read_unlock();
+ if (sync_page_io(rdev, sect, s<<9,
+ conf->tmppage, 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;
} while (!success && d != read_disk);

if (!success) {
@@ -2094,11 +2095,17 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
if (d==0)
d = conf->raid_disks * 2;
d--;
- rdev = conf->mirrors[d].rdev;
+ rcu_read_lock();
+ rdev = rcu_dereference(conf->mirrors[d].rdev);
if (rdev &&
- !test_bit(Faulty, &rdev->flags))
+ !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) {
@@ -2106,9 +2113,12 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
if (d==0)
d = conf->raid_disks * 2;
d--;
- rdev = conf->mirrors[d].rdev;
+ rcu_read_lock();
+ rdev = rcu_dereference(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);
@@ -2117,10 +2127,12 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
"(%d sectors at %llu on %s)\n",
mdname(mddev), s,
(unsigned long long)(sect +
- rdev->data_offset),
+ rdev->data_offset),
bdevname(rdev->bdev, b));
}
- }
+ rdev_dec_pending(rdev, mddev);
+ } else
+ rcu_read_unlock();
}
sectors -= s;
sect += s;