[PATCH 4.14 20/43] dm log writes: make sure super sector log updates are written in order

[Greg Kroah-Hartman]

From: zhangyi (F) <yi.zh...@huawei.com>

commit 211ad4b733037f66f9be0a79eade3da7ab11cbb8 upstream.

Currently, although we submit super bios in order (and super.nr_entries
is incremented by each logged entry), submit_bio() is async so each
super sector may not be written to log device in order and then the
final nr_entries may be smaller than it should be.

This problem can be reproduced by the xfstests generic/455 with ext4:

  QA output created by 455
 -Silence is golden
 +mark 'end' does not exist

Fix this by serializing submission of super sectors to make sure each
is written to the log disk in order.

Fixes: 0e9cebe724597 ("dm: add log writes target")
Cc: sta...@vger.kernel.org
Signed-off-by: zhangyi (F) <yi.zh...@huawei.com>
Suggested-by: Josef Bacik <jo...@toxicpanda.com>
Reviewed-by: Josef Bacik <jo...@toxicpanda.com>
Signed-off-by: Mike Snitzer <snit...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/md/dm-log-writes.c |   23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

--- a/drivers/md/dm-log-writes.c
+++ b/drivers/md/dm-log-writes.c
@@ -57,6 +57,7 @@
 
 #define WRITE_LOG_VERSION 1ULL
 #define WRITE_LOG_MAGIC 0x6a736677736872ULL
+#define WRITE_LOG_SUPER_SECTOR 0
 
 /*
  * The disk format for this is braindead simple.
@@ -112,6 +113,7 @@ struct log_writes_c {
        struct list_head logging_blocks;
        wait_queue_head_t wait;
        struct task_struct *log_kthread;
+       struct completion super_done;
 };
 
 struct pending_block {
@@ -177,6 +179,14 @@ static void log_end_io(struct bio *bio)
        bio_put(bio);
 }
 
+static void log_end_super(struct bio *bio)
+{
+       struct log_writes_c *lc = bio->bi_private;
+
+       complete(&lc->super_done);
+       log_end_io(bio);
+}
+
 /*
  * Meant to be called if there is an error, it will free all the pages
  * associated with the block.
@@ -212,7 +222,8 @@ static int write_metadata(struct log_wri
        bio->bi_iter.bi_size = 0;
        bio->bi_iter.bi_sector = sector;
        bio_set_dev(bio, lc->logdev->bdev);
-       bio->bi_end_io = log_end_io;
+       bio->bi_end_io = (sector == WRITE_LOG_SUPER_SECTOR) ?
+                         log_end_super : log_end_io;
        bio->bi_private = lc;
        bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
 
@@ -334,11 +345,18 @@ static int log_super(struct log_writes_c
        super.nr_entries = cpu_to_le64(lc->logged_entries);
        super.sectorsize = cpu_to_le32(lc->sectorsize);
 
-       if (write_metadata(lc, &super, sizeof(super), NULL, 0, 0)) {
+       if (write_metadata(lc, &super, sizeof(super), NULL, 0,
+                          WRITE_LOG_SUPER_SECTOR)) {
                DMERR("Couldn't write super");
                return -1;
        }
 
+       /*
+        * Super sector should be writen in-order, otherwise the
+        * nr_entries could be rewritten incorrectly by an old bio.
+        */
+       wait_for_completion_io(&lc->super_done);
+
        return 0;
 }
 
@@ -447,6 +465,7 @@ static int log_writes_ctr(struct dm_targ
        INIT_LIST_HEAD(&lc->unflushed_blocks);
        INIT_LIST_HEAD(&lc->logging_blocks);
        init_waitqueue_head(&lc->wait);
+       init_completion(&lc->super_done);
        atomic_set(&lc->io_blocks, 0);
        atomic_set(&lc->pending_blocks, 0);