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Subject[PATCH 3.18 087/120] dm thin metadata: try to avoid ever aborting transactions
Date
3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Thornber <ejt@redhat.com>

[ Upstream commit 3ab91828166895600efd9cdc3a0eb32001f7204a ]

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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/dm-thin-metadata.c | 36 ++++++++++++++++++++
drivers/md/dm-thin.c | 73 +++++++++++++++++++++++++++++++++++++-----
2 files changed, 100 insertions(+), 9 deletions(-)

--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -191,6 +191,12 @@ struct dm_pool_metadata {
bool read_only:1;

/*
+ * 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.
@@ -824,6 +830,22 @@ static int __commit_transaction(struct d
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)
@@ -858,6 +880,8 @@ struct dm_pool_metadata *dm_pool_metadat
return ERR_PTR(r);
}

+ __set_metadata_reserve(pmd);
+
return pmd;
}

@@ -1625,6 +1649,13 @@ int dm_pool_get_free_metadata_block_coun
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;
@@ -1746,8 +1777,11 @@ int dm_pool_resize_metadata_dev(struct d
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;
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -140,7 +140,13 @@ 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_OUT_OF_METADATA_SPACE,
PM_READ_ONLY, /* metadata may not be changed */
+
PM_FAIL, /* all I/O fails */
};

@@ -994,7 +1000,35 @@ static void set_pool_mode(struct pool *p

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;
@@ -1020,14 +1054,16 @@ 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
- check_for_space(pool);
+ else {
+ check_for_metadata_space(pool);
+ check_for_data_space(pool);
+ }

return r;
}
@@ -1093,6 +1129,19 @@ static int alloc_data_block(struct thin_
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;
}

@@ -1124,6 +1173,7 @@ static int should_error_unserviceable_bi
case PM_OUT_OF_DATA_SPACE:
return pool->pf.error_if_no_space ? -ENOSPC : 0;

+ case PM_OUT_OF_METADATA_SPACE:
case PM_READ_ONLY:
case PM_FAIL:
return -EIO;
@@ -1823,8 +1873,9 @@ static void set_pool_mode(struct pool *p
error_retry_list(pool);
break;

+ case PM_OUT_OF_METADATA_SPACE:
case PM_READ_ONLY:
- if (old_mode != new_mode)
+ if (!is_read_only_pool_mode(old_mode))
notify_of_pool_mode_change(pool, "read-only");
dm_pool_metadata_read_only(pool->pmd);
pool->process_bio = process_bio_read_only;
@@ -2727,6 +2778,10 @@ static int maybe_resize_metadata_dev(str
DMINFO("%s: growing the metadata device from %llu to %llu blocks",
dm_device_name(pool->pool_md),
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);
@@ -2974,7 +3029,7 @@ static int pool_message(struct dm_target
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",
dm_device_name(pool->pool_md));
return -EINVAL;
@@ -3047,6 +3102,7 @@ static void pool_status(struct dm_target
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;
@@ -3117,9 +3173,10 @@ static void pool_status(struct dm_target
else
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 ");
else
DMEMIT("rw ");

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