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>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index e1feb87afc6c..7301631abe04 100644
--- 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);
 }
 
 /*