[PATCH] bcache: prevent crash on changing writeback_running

[Stefan Bader]

commit a664d0f05a2e ("bcache: fix crash on shutdown in passthrough mode")

added a safeguard in the shutdown case. At least while not being
attached it is also possible to trigger a kernel bug by writing into
writeback_running. This change  adds the same check before trying to
wake up the thread for that case.

Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
---
 drivers/md/bcache/writeback.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -63,7 +63,8 @@ static inline bool should_writeback(stru

 static inline void bch_writeback_queue(struct cached_dev *dc)
 {
- wake_up_process(dc->writeback_thread);
+ if (!IS_ERR_OR_NULL(dc->writeback_thread))
+ wake_up_process(dc->writeback_thread);
 }

 static inline void bch_writeback_add(struct cached_dev *dc)
Subject: [PATCH] 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@xxxxxxxxx>
---
 drivers/md/bcache/writeback.c | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -323,6 +323,10 @@ void bcache_dev_sectors_dirty_add(struct

 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_d
  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)
---

-- 

Denis
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