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Subject[PATCH 5.4 54/80] dm clone metadata: Use a two phase commit
Date
From: Nikos Tsironis <ntsironis@arrikto.com>

commit 8fdbfe8d1690e8a38d497d83a30607d0d90cc15a upstream.

Split the metadata commit in two parts:

1. dm_clone_metadata_pre_commit(): Prepare the current transaction for
committing. After this is called, all subsequent metadata updates,
done through either dm_clone_set_region_hydrated() or
dm_clone_cond_set_range(), will be part of the next transaction.

2. dm_clone_metadata_commit(): Actually commit the current transaction
to disk and start a new transaction.

This is required by the following commit. It allows dm-clone to flush
the destination device after step (1) to ensure that all freshly
hydrated regions, for which we are updating the metadata, are properly
written to non-volatile storage and won't be lost in case of a crash.

Fixes: 7431b7835f55 ("dm: add clone target")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/dm-clone-metadata.c | 46 ++++++++++++++++++++++++++++++++---------
drivers/md/dm-clone-metadata.h | 17 +++++++++++++++
drivers/md/dm-clone-target.c | 7 +++++-
3 files changed, 60 insertions(+), 10 deletions(-)

--- a/drivers/md/dm-clone-metadata.c
+++ b/drivers/md/dm-clone-metadata.c
@@ -127,6 +127,9 @@ struct dm_clone_metadata {
struct dirty_map dmap[2];
struct dirty_map *current_dmap;

+ /* Protected by lock */
+ struct dirty_map *committing_dmap;
+
/*
* In core copy of the on-disk bitmap to save constantly doing look ups
* on disk.
@@ -511,6 +514,7 @@ static int dirty_map_init(struct dm_clon
}

cmd->current_dmap = &cmd->dmap[0];
+ cmd->committing_dmap = NULL;

return 0;
}
@@ -775,16 +779,18 @@ static int __flush_dmap(struct dm_clone_
return 0;
}

-int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
+int dm_clone_metadata_pre_commit(struct dm_clone_metadata *cmd)
{
- int r = -EPERM;
+ int r = 0;
unsigned long flags;
struct dirty_map *dmap, *next_dmap;

down_write(&cmd->lock);

- if (cmd->fail_io || dm_bm_is_read_only(cmd->bm))
+ if (cmd->fail_io || dm_bm_is_read_only(cmd->bm)) {
+ r = -EPERM;
goto out;
+ }

/* Get current dirty bitmap */
dmap = cmd->current_dmap;
@@ -796,7 +802,7 @@ int dm_clone_metadata_commit(struct dm_c
* The last commit failed, so we don't have a clean dirty-bitmap to
* use.
*/
- if (WARN_ON(next_dmap->changed)) {
+ if (WARN_ON(next_dmap->changed || cmd->committing_dmap)) {
r = -EINVAL;
goto out;
}
@@ -806,11 +812,33 @@ int dm_clone_metadata_commit(struct dm_c
cmd->current_dmap = next_dmap;
spin_unlock_irqrestore(&cmd->bitmap_lock, flags);

- /*
- * No one is accessing the old dirty bitmap anymore, so we can flush
- * it.
- */
- r = __flush_dmap(cmd, dmap);
+ /* Set old dirty bitmap as currently committing */
+ cmd->committing_dmap = dmap;
+out:
+ up_write(&cmd->lock);
+
+ return r;
+}
+
+int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
+{
+ int r = -EPERM;
+
+ down_write(&cmd->lock);
+
+ if (cmd->fail_io || dm_bm_is_read_only(cmd->bm))
+ goto out;
+
+ if (WARN_ON(!cmd->committing_dmap)) {
+ r = -EINVAL;
+ goto out;
+ }
+
+ r = __flush_dmap(cmd, cmd->committing_dmap);
+ if (!r) {
+ /* Clear committing dmap */
+ cmd->committing_dmap = NULL;
+ }
out:
up_write(&cmd->lock);

--- a/drivers/md/dm-clone-metadata.h
+++ b/drivers/md/dm-clone-metadata.h
@@ -73,7 +73,23 @@ void dm_clone_metadata_close(struct dm_c

/*
* Commit dm-clone metadata to disk.
+ *
+ * We use a two phase commit:
+ *
+ * 1. dm_clone_metadata_pre_commit(): Prepare the current transaction for
+ * committing. After this is called, all subsequent metadata updates, done
+ * through either dm_clone_set_region_hydrated() or
+ * dm_clone_cond_set_range(), will be part of the **next** transaction.
+ *
+ * 2. dm_clone_metadata_commit(): Actually commit the current transaction to
+ * disk and start a new transaction.
+ *
+ * This allows dm-clone to flush the destination device after step (1) to
+ * ensure that all freshly hydrated regions, for which we are updating the
+ * metadata, are properly written to non-volatile storage and won't be lost in
+ * case of a crash.
*/
+int dm_clone_metadata_pre_commit(struct dm_clone_metadata *cmd);
int dm_clone_metadata_commit(struct dm_clone_metadata *cmd);

/*
@@ -110,6 +126,7 @@ int dm_clone_metadata_abort(struct dm_cl
* Switches metadata to a read only mode. Once read-only mode has been entered
* the following functions will return -EPERM:
*
+ * dm_clone_metadata_pre_commit()
* dm_clone_metadata_commit()
* dm_clone_set_region_hydrated()
* dm_clone_cond_set_range()
--- a/drivers/md/dm-clone-target.c
+++ b/drivers/md/dm-clone-target.c
@@ -1120,8 +1120,13 @@ static int commit_metadata(struct clone
goto out;
}

- r = dm_clone_metadata_commit(clone->cmd);
+ r = dm_clone_metadata_pre_commit(clone->cmd);
+ if (unlikely(r)) {
+ __metadata_operation_failed(clone, "dm_clone_metadata_pre_commit", r);
+ goto out;
+ }

+ r = dm_clone_metadata_commit(clone->cmd);
if (unlikely(r)) {
__metadata_operation_failed(clone, "dm_clone_metadata_commit", r);
goto out;

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