bcache: Change refill_dirty() to always scan entire disk if necessary

Previously, it would only scan the entire disk if it was starting from
the very start of the disk - i.e. if the previous scan got to the end.

This was broken by refill_full_stripes(), which updates last_scanned so
that refill_dirty was never triggering the searched_from_start path.

But if we change refill_dirty() to always scan the entire disk if
necessary, regardless of what last_scanned was, the code gets cleaner
and we fix that bug too.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 30 insertions, 7 deletions

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index b23f88d9f18c..b9346cd9cda1 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -323,6 +323,10 @@ void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode,
 
 static bool dirty_pred(struct keybuf *buf, struct bkey *k)
 {
+        struct cached_dev *dc = container_of(buf, struct cached_dev, writeback_keys);
+
+        BUG_ON(KEY_INODE(k) != dc->disk.id);
+
         return KEY_DIRTY(k);
 }
 
@@ -372,11 +376,24 @@ next:
         }
 }
 
+/*
+ * Returns true if we scanned the entire disk
+ */
 static bool refill_dirty(struct cached_dev *dc)
 {
         struct keybuf *buf = &dc->writeback_keys;
+        struct bkey start = KEY(dc->disk.id, 0, 0);
         struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
-        bool searched_from_start = false;
+        struct bkey start_pos;
+
+        /*
+         * make sure keybuf pos is inside the range for this disk - at bringup
+         * we might not be attached yet so this disk's inode nr isn't
+         * initialized then
+         */
+        if (bkey_cmp(&buf->last_scanned, &start) < 0 ||
+            bkey_cmp(&buf->last_scanned, &end) > 0)
+                buf->last_scanned = start;
 
         if (dc->partial_stripes_expensive) {
                 refill_full_stripes(dc);
@@ -384,14 +401,20 @@ static bool refill_dirty(struct cached_dev *dc)
                         return false;
         }
 
-        if (bkey_cmp(&buf->last_scanned, &end) >= 0) {
-                buf->last_scanned = KEY(dc->disk.id, 0, 0);
-                searched_from_start = true;
-        }
-
+        start_pos = buf->last_scanned;
         bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
 
-        return bkey_cmp(&buf->last_scanned, &end) >= 0 && searched_from_start;
+        if (bkey_cmp(&buf->last_scanned, &end) < 0)
+                return false;
+
+        /*
+         * If we get to the end start scanning again from the beginning, and
+         * only scan up to where we initially started scanning from:
+         */
+        buf->last_scanned = start;
+        bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred);
+
+        return bkey_cmp(&buf->last_scanned, &start_pos) >= 0;
 }
 
 static int bch_writeback_thread(void *arg)