raid5-ppl: fix handling flush requests

Add missing bio completion. Without this any flush request would hang.

Fixes: 1532d9e8 ("raid5-ppl: PPL support for disks with write-back cache enabled")
Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: Shaohua Li <sh.li@alibaba-inc.com>

drivers/md/raid5-log.h

@@ -44,6 +44,7 @@ extern void ppl_write_stripe_run(struct r5conf *conf);
 extern void ppl_stripe_write_finished(struct stripe_head *sh);
 extern int ppl_modify_log(struct r5conf *conf, struct md_rdev *rdev, bool add);
 extern void ppl_quiesce(struct r5conf *conf, int quiesce);
+extern int ppl_handle_flush_request(struct r5l_log *log, struct bio *bio);
 
 static inline bool raid5_has_ppl(struct r5conf *conf)
 {
@@ -104,7 +105,7 @@ static inline int log_handle_flush_request(struct r5conf *conf, struct bio *bio)
 	if (conf->log)
 		ret = r5l_handle_flush_request(conf->log, bio);
 	else if (raid5_has_ppl(conf))
-		ret = 0;
+		ret = ppl_handle_flush_request(conf->log, bio);
 
 	return ret;
 }

drivers/md/raid5-ppl.c

@@ -693,6 +693,16 @@ void ppl_quiesce(struct r5conf *conf, int quiesce)
 	}
 }
 
+int ppl_handle_flush_request(struct r5l_log *log, struct bio *bio)
+{
+	if (bio->bi_iter.bi_size == 0) {
+		bio_endio(bio);
+		return 0;
+	}
+	bio->bi_opf &= ~REQ_PREFLUSH;
+	return -EAGAIN;
+}
+
 void ppl_stripe_write_finished(struct stripe_head *sh)
 {
 	struct ppl_io_unit *io;