dm thin metadata: try to avoid ever aborting transactions
Committing a transaction can consume some metadata of it's own, we now
reserve a small amount of metadata to cover this. Free metadata
reported by the kernel will not include this reserve.
If any of the reserve has been used after a commit we enter a new
internal state PM_OUT_OF_METADATA_SPACE. This is reported as
PM_READ_ONLY, so no userland changes are needed. If the metadata
device is resized the pool will move back to PM_WRITE.
These changes mean we never need to abort and rollback a transaction due
to running out of metadata space. This is particularly important
because there have been a handful of reports of data corruption against
DM thin-provisioning that can all be attributed to the thin-pool having
ran out of metadata space.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 7214202..74f6770 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -189,6 +189,12 @@ struct dm_pool_metadata {
sector_t data_block_size;
/*
+ * We reserve a section of the metadata for commit overhead.
+ * All reported space does *not* include this.
+ */
+ dm_block_t metadata_reserve;
+
+ /*
* Set if a transaction has to be aborted but the attempt to roll back
* to the previous (good) transaction failed. The only pool metadata
* operation possible in this state is the closing of the device.
@@ -816,6 +822,22 @@ static int __commit_transaction(struct dm_pool_metadata *pmd)
return dm_tm_commit(pmd->tm, sblock);
}
+static void __set_metadata_reserve(struct dm_pool_metadata *pmd)
+{
+ int r;
+ dm_block_t total;
+ dm_block_t max_blocks = 4096; /* 16M */
+
+ r = dm_sm_get_nr_blocks(pmd->metadata_sm, &total);
+ if (r) {
+ DMERR("could not get size of metadata device");
+ pmd->metadata_reserve = max_blocks;
+ } else {
+ sector_div(total, 10);
+ pmd->metadata_reserve = min(max_blocks, total);
+ }
+}
+
struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev,
sector_t data_block_size,
bool format_device)
@@ -849,6 +871,8 @@ struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev,
return ERR_PTR(r);
}
+ __set_metadata_reserve(pmd);
+
return pmd;
}
@@ -1820,6 +1844,13 @@ int dm_pool_get_free_metadata_block_count(struct dm_pool_metadata *pmd,
down_read(&pmd->root_lock);
if (!pmd->fail_io)
r = dm_sm_get_nr_free(pmd->metadata_sm, result);
+
+ if (!r) {
+ if (*result < pmd->metadata_reserve)
+ *result = 0;
+ else
+ *result -= pmd->metadata_reserve;
+ }
up_read(&pmd->root_lock);
return r;
@@ -1932,8 +1963,11 @@ int dm_pool_resize_metadata_dev(struct dm_pool_metadata *pmd, dm_block_t new_cou
int r = -EINVAL;
down_write(&pmd->root_lock);
- if (!pmd->fail_io)
+ if (!pmd->fail_io) {
r = __resize_space_map(pmd->metadata_sm, new_count);
+ if (!r)
+ __set_metadata_reserve(pmd);
+ }
up_write(&pmd->root_lock);
return r;
