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dm clone metadata: Use a two phase commit

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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: 7431b7835f ("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>
This commit is contained in:
Nikos Tsironis 2019-12-04 16:06:53 +02:00 committed by Mike Snitzer
parent e6a505f3f9
commit 8fdbfe8d16
3 changed files with 60 additions and 10 deletions
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46
drivers/md/dm-clone-metadata.c
View File

@ -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_clone_metadata *cmd)
}
cmd->current_dmap = &cmd->dmap[0];
cmd->committing_dmap = NULL;
return 0;
}
@ -775,15 +779,17 @@ static int __flush_dmap(struct dm_clone_metadata *cmd, struct dirty_map *dmap)
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;
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;
@ -795,7 +801,7 @@ int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
* 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;
}
@ -805,11 +811,33 @@ int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
cmd->current_dmap = next_dmap;
spin_unlock_irq(&cmd->bitmap_lock);
/*
* 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);

17
drivers/md/dm-clone-metadata.h
View File

@ -75,7 +75,23 @@ void dm_clone_metadata_close(struct dm_clone_metadata *cmd);
/*
* 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);
/*
@ -112,6 +128,7 @@ int dm_clone_metadata_abort(struct dm_clone_metadata *cmd);
* 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()

7
drivers/md/dm-clone-target.c
View File

@ -1122,8 +1122,13 @@ static int commit_metadata(struct clone *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;