md/raid5: use seqcount to protect access to shape in make_request.

make_request() access various shape parameters (raid_disks, chunk_size
etc) which might be changed by raid5_start_reshape().

If the later is called at and awkward time during the form, the wrong
stripe_head might be used.

So introduce a 'seqcount' and after finding a stripe_head make sure
there is no reason to expect that we got the wrong one.

Signed-off-by: NeilBrown <neilb@suse.de>

2 files changed, 14 insertions, 1 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index d79ecd903269..4263df11d597 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4408,8 +4408,10 @@ static void make_request(struct mddev *mddev, struct bio * bi)
         for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
                 DEFINE_WAIT(w);
                 int previous;
+                int seq;
 
         retry:
+                seq = read_seqcount_begin(&conf->gen_lock);
                 previous = 0;
                 prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
                 if (unlikely(conf->reshape_progress != MaxSector)) {
@@ -4442,7 +4444,7 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                                                   previous,
                                                   &dd_idx, NULL);
                 pr_debug("raid456: make_request, sector %llu logical %llu\n",
-                        (unsigned long long)new_sector, 
+                        (unsigned long long)new_sector,
                         (unsigned long long)logical_sector);
 
                 sh = get_active_stripe(conf, new_sector, previous,
@@ -4471,6 +4473,13 @@ static void make_request(struct mddev *mddev, struct bio * bi)
                                         goto retry;
                                 }
                         }
+                        if (read_seqcount_retry(&conf->gen_lock, seq)) {
+                                /* Might have got the wrong stripe_head
+                                 * by accident
+                                 */
+                                release_stripe(sh);
+                                goto retry;
+                        }
 
                         if (rw == WRITE &&
                             logical_sector >= mddev->suspend_lo &&
@@ -5437,6 +5446,7 @@ static struct r5conf *setup_conf(struct mddev *mddev)
         if (alloc_thread_groups(conf, 0))
                 goto abort;
         spin_lock_init(&conf->device_lock);
+        seqcount_init(&conf->gen_lock);
         init_waitqueue_head(&conf->wait_for_stripe);
         init_waitqueue_head(&conf->wait_for_overlap);
         INIT_LIST_HEAD(&conf->handle_list);
@@ -6249,6 +6259,7 @@ static int raid5_start_reshape(struct mddev *mddev)
 
         atomic_set(&conf->reshape_stripes, 0);
         spin_lock_irq(&conf->device_lock);
+        write_seqcount_begin(&conf->gen_lock);
         conf->previous_raid_disks = conf->raid_disks;
         conf->raid_disks += mddev->delta_disks;
         conf->prev_chunk_sectors = conf->chunk_sectors;
@@ -6265,6 +6276,7 @@ static int raid5_start_reshape(struct mddev *mddev)
         else
                 conf->reshape_progress = 0;
         conf->reshape_safe = conf->reshape_progress;
+        write_seqcount_end(&conf->gen_lock);
         spin_unlock_irq(&conf->device_lock);
 
         /* Add some new drives, as many as will fit.
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 105366371fbf..435b12d58165 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -400,6 +400,7 @@ struct r5conf {
         int                     prev_chunk_sectors;
         int                     prev_algo;
         short                   generation; /* increments with every reshape */
+        seqcount_t              gen_lock;       /* lock against generation changes */
         unsigned long           reshape_checkpoint; /* Time we last updated
                                                      * metadata */
         long long               min_offset_diff; /* minimum difference between