[PATCH 4.19 39/72] dm log writes: make sure super sector log updates are written in order

Greg Kroah-Hartman
2019-07-02T08:13:56Z

From: zhangyi (F) <yi.zhang@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: stable@vger.kernel.org
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Suggested-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@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
@@ -60,6 +60,7 @@

#define WRITE_LOG_VERSION 1ULL
#define WRITE_LOG_MAGIC 0x6a736677736872ULL
+#define WRITE_LOG_SUPER_SECTOR 0

/*
* The disk format for this is braindead simple.
@@ -115,6 +116,7 @@ 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 {
@@ -180,6 +182,14 @@ 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.
@@ -215,7 +225,8 @@ 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);

@@ -418,11 +429,18 @@ 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;
}

@@ -531,6 +549,7 @@ 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);