[RFC PATCH v2 13/16] bcache: fix fifo index swapping condition in btree_flush_write()

[Coly Li <colyli@suse.de>]

Current journal_max_cmp() and journal_min_cmp() assume that smaller fifo
index indicating elder journal entries, but this is only true when fifo
index is not swapped.

Fifo structure journal.pin is implemented by a cycle buffer, if the head
index reaches highest location of the cycle buffer, it will be swapped
to 0. Once the swapping happens, it means a smaller fifo index might be
associated to a newer journal entry. So the btree node with oldest
journal entry won't be selected by btree_flush_write() to flush out to
cache device. The result is, the oldest journal entries may always has
no chance to be written into cache device, and after a reboot
bch_journal_replay() may complain some journal entries are missing.

This patch handles the fifo index swapping conditions properly, then in
btree_flush_write() the btree node with oldest journal entry can be
slected from c->flush_btree correctly.

Cc: stable@vger.kernel.org
Signed-off-by: Coly Li <colyli@suse.de>
---
 drivers/md/bcache/journal.c | 47 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 41 insertions(+), 6 deletions(-)

diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index bdb6f9cefe48..bc0e01151155 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -464,12 +464,47 @@ int bch_journal_replay(struct cache_set *s, struct list_head *list)
 }
 
 /* Journalling */
-#define journal_max_cmp(l, r) \
-	(fifo_idx(&c->journal.pin, btree_current_write(l)->journal) < \
-	 fifo_idx(&(c)->journal.pin, btree_current_write(r)->journal))
-#define journal_min_cmp(l, r) \
-	(fifo_idx(&c->journal.pin, btree_current_write(l)->journal) > \
-	 fifo_idx(&(c)->journal.pin, btree_current_write(r)->journal))
+#define journal_max_cmp(l, r)						\
+({									\
+	int l_idx, r_idx, f_idx, b_idx;					\
+	bool _ret = true;						\
+									\
+	l_idx = fifo_idx(&c->journal.pin, btree_current_write(l)->journal); \
+	r_idx = fifo_idx(&c->journal.pin, btree_current_write(r)->journal); \
+	f_idx = c->journal.pin.front;					\
+	b_idx = c->journal.pin.back;					\
+									\
+	_ret = (l_idx < r_idx);						\
+	/* in case fifo back pointer is swapped */			\
+	if (b_idx < f_idx) { 						\
+		if (l_idx <= b_idx && r_idx >= f_idx)			\
+			_ret = false;					\
+		else if (l_idx >= f_idx && r_idx <= b_idx)		\
+			_ret = true;					\
+	}								\
+	_ret;								\
+})
+
+#define journal_min_cmp(l, r)						\
+({									\
+	int l_idx, r_idx, f_idx, b_idx;					\
+	bool _ret = true;						\
+									\
+	l_idx = fifo_idx(&c->journal.pin, btree_current_write(l)->journal); \
+	r_idx = fifo_idx(&c->journal.pin, btree_current_write(r)->journal); \
+	f_idx = c->journal.pin.front;					\
+	b_idx = c->journal.pin.back;					\
+									\
+	_ret = (l_idx > r_idx);						\
+	/* in case fifo back pointer is swapped */			\
+	if (b_idx < f_idx) {						\
+		if (l_idx <= b_idx && r_idx >= f_idx)			\
+			_ret = true;					\
+		else if (l_idx >= f_idx && r_idx <= b_idx)		\
+			_ret = false;					\
+	}								\
+	_ret;								\
+})
 
 static void btree_flush_write(struct cache_set *c)
 {
-- 
2.16.4