Commit 3ab91828 authored by Joe Thornber's avatar Joe Thornber Committed by Mike Snitzer
Browse files

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: default avatarJoe Thornber <>
Signed-off-by: default avatarMike Snitzer <>
parent 5380c05b
......@@ -188,6 +188,12 @@ struct dm_pool_metadata {
unsigned long flags;
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
......@@ -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);
return pmd;
......@@ -1820,6 +1844,13 @@ int dm_pool_get_free_metadata_block_count(struct dm_pool_metadata *pmd,
if (!pmd->fail_io)
r = dm_sm_get_nr_free(pmd->metadata_sm, result);
if (!r) {
if (*result < pmd->metadata_reserve)
*result = 0;
*result -= pmd->metadata_reserve;
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;
if (!pmd->fail_io)
if (!pmd->fail_io) {
r = __resize_space_map(pmd->metadata_sm, new_count);
if (!r)
return r;
......@@ -200,7 +200,13 @@ struct dm_thin_new_mapping;
enum pool_mode {
PM_WRITE, /* metadata may be changed */
PM_OUT_OF_DATA_SPACE, /* metadata may be changed, though data may not be allocated */
* Like READ_ONLY, except may switch back to WRITE on metadata resize. Reported as READ_ONLY.
PM_READ_ONLY, /* metadata may not be changed */
PM_FAIL, /* all I/O fails */
......@@ -1371,7 +1377,35 @@ static void set_pool_mode(struct pool *pool, enum pool_mode new_mode);
static void requeue_bios(struct pool *pool);
static void check_for_space(struct pool *pool)
static bool is_read_only_pool_mode(enum pool_mode mode)
return (mode == PM_OUT_OF_METADATA_SPACE || mode == PM_READ_ONLY);
static bool is_read_only(struct pool *pool)
return is_read_only_pool_mode(get_pool_mode(pool));
static void check_for_metadata_space(struct pool *pool)
int r;
const char *ooms_reason = NULL;
dm_block_t nr_free;
r = dm_pool_get_free_metadata_block_count(pool->pmd, &nr_free);
if (r)
ooms_reason = "Could not get free metadata blocks";
else if (!nr_free)
ooms_reason = "No free metadata blocks";
if (ooms_reason && !is_read_only(pool)) {
DMERR("%s", ooms_reason);
set_pool_mode(pool, PM_OUT_OF_METADATA_SPACE);
static void check_for_data_space(struct pool *pool)
int r;
dm_block_t nr_free;
......@@ -1397,14 +1431,16 @@ static int commit(struct pool *pool)
int r;
if (get_pool_mode(pool) >= PM_READ_ONLY)
if (get_pool_mode(pool) >= PM_OUT_OF_METADATA_SPACE)
return -EINVAL;
r = dm_pool_commit_metadata(pool->pmd);
if (r)
metadata_operation_failed(pool, "dm_pool_commit_metadata", r);
else {
return r;
......@@ -1470,6 +1506,19 @@ static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
return r;
r = dm_pool_get_free_metadata_block_count(pool->pmd, &free_blocks);
if (r) {
metadata_operation_failed(pool, "dm_pool_get_free_metadata_block_count", r);
return r;
if (!free_blocks) {
/* Let's commit before we use up the metadata reserve. */
r = commit(pool);
if (r)
return r;
return 0;
......@@ -1501,6 +1550,7 @@ static blk_status_t should_error_unserviceable_bio(struct pool *pool)
return pool->pf.error_if_no_space ? BLK_STS_NOSPC : 0;
case PM_FAIL:
......@@ -2464,8 +2514,9 @@ static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
if (old_mode != new_mode)
if (!is_read_only_pool_mode(old_mode))
notify_of_pool_mode_change(pool, "read-only");
pool->process_bio = process_bio_read_only;
......@@ -3403,6 +3454,10 @@ static int maybe_resize_metadata_dev(struct dm_target *ti, bool *need_commit)
DMINFO("%s: growing the metadata device from %llu to %llu blocks",
sb_metadata_dev_size, metadata_dev_size);
if (get_pool_mode(pool) == PM_OUT_OF_METADATA_SPACE)
set_pool_mode(pool, PM_WRITE);
r = dm_pool_resize_metadata_dev(pool->pmd, metadata_dev_size);
if (r) {
metadata_operation_failed(pool, "dm_pool_resize_metadata_dev", r);
......@@ -3707,7 +3762,7 @@ static int pool_message(struct dm_target *ti, unsigned argc, char **argv,
struct pool_c *pt = ti->private;
struct pool *pool = pt->pool;
if (get_pool_mode(pool) >= PM_READ_ONLY) {
if (get_pool_mode(pool) >= PM_OUT_OF_METADATA_SPACE) {
DMERR("%s: unable to service pool target messages in READ_ONLY or FAIL mode",
......@@ -3781,6 +3836,7 @@ static void pool_status(struct dm_target *ti, status_type_t type,
dm_block_t nr_blocks_data;
dm_block_t nr_blocks_metadata;
dm_block_t held_root;
enum pool_mode mode;
char buf[BDEVNAME_SIZE];
char buf2[BDEVNAME_SIZE];
struct pool_c *pt = ti->private;
......@@ -3851,9 +3907,10 @@ static void pool_status(struct dm_target *ti, status_type_t type,
DMEMIT("- ");
if (pool->pf.mode == PM_OUT_OF_DATA_SPACE)
mode = get_pool_mode(pool);
if (mode == PM_OUT_OF_DATA_SPACE)
DMEMIT("out_of_data_space ");
else if (pool->pf.mode == PM_READ_ONLY)
else if (is_read_only_pool_mode(mode))
DMEMIT("ro ");
DMEMIT("rw ");
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