md: avoid races when stopping resync.

There has been a race in raid10 and raid1 for a long time
which has only recently started showing up due to a scheduler changed.

When a sync_read request finishes, as soon as reschedule_retry
is called, another thread can mark the resync request as having
completed, so md_do_sync can finish, ->stop can be called, and
->conf can be freed.  So using conf after reschedule_retry is not
safe.

Similarly, when finishing a sync_write, calling md_done_sync must be
the last thing we do, as it allows a chain of events which will free
conf and other data structures.

The first of these requires action in raid10.c
The second requires action in raid1.c and raid10.c

Cc: stable@kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 01e3cffd03b8fd28dae613614f3efd10c04f2416..e2466425d9cad798edf40858183404408b319e3d 100644 (file)
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1237,8 +1237,9 @@ static void end_sync_write(struct bio *bio, int error)
        update_head_pos(mirror, r1_bio);
 
        if (atomic_dec_and_test(&r1_bio->remaining)) {
-               md_done_sync(mddev, r1_bio->sectors, uptodate);
+               sector_t s = r1_bio->sectors;
                put_buf(r1_bio);
+               md_done_sync(mddev, s, uptodate);
        }
 }
 

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index e1feb87afc6c827027d193e8e50003e0b1ca316b..7301631abe0453a4791dec55ba0eff84912876c3 100644 (file)
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1236,6 +1236,7 @@ static void end_sync_read(struct bio *bio, int error)
        /* for reconstruct, we always reschedule after a read.
         * for resync, only after all reads
         */
+       rdev_dec_pending(conf->mirrors[d].rdev, conf->mddev);
        if (test_bit(R10BIO_IsRecover, &r10_bio->state) ||
            atomic_dec_and_test(&r10_bio->remaining)) {
                /* we have read all the blocks,
@@ -1243,7 +1244,6 @@ static void end_sync_read(struct bio *bio, int error)
                 */
                reschedule_retry(r10_bio);
        }
-       rdev_dec_pending(conf->mirrors[d].rdev, conf->mddev);
 }
 
 static void end_sync_write(struct bio *bio, int error)
@@ -1264,11 +1264,13 @@ static void end_sync_write(struct bio *bio, int error)
 
        update_head_pos(i, r10_bio);
 
+       rdev_dec_pending(conf->mirrors[d].rdev, mddev);
        while (atomic_dec_and_test(&r10_bio->remaining)) {
                if (r10_bio->master_bio == NULL) {
                        /* the primary of several recovery bios */
-                       md_done_sync(mddev, r10_bio->sectors, 1);
+                       sector_t s = r10_bio->sectors;
                        put_buf(r10_bio);
+                       md_done_sync(mddev, s, 1);
                        break;
                } else {
                        r10bio_t *r10_bio2 = (r10bio_t *)r10_bio->master_bio;
@@ -1276,7 +1278,6 @@ static void end_sync_write(struct bio *bio, int error)
                        r10_bio = r10_bio2;
                }
        }
-       rdev_dec_pending(conf->mirrors[d].rdev, mddev);
 }
 
 /*