dm thin: switch to read-only mode if metadata space is exhausted

Switch the thin pool to read-only mode in alloc_data_block() if
dm_pool_alloc_data_block() fails because the pool's metadata space is
exhausted.

Differentiate between data and metadata space in messages about no
free space available.

This issue was noticed with the device-mapper-test-suite using:
dmtest run --suite thin-provisioning -n /exhausting_metadata_space_causes_fail_mode/

The quantity of errors logged in this case must be reduced.

before patch:

device-mapper: thin: 253:4: reached low water mark for metadata device: sending event.
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
<snip ... these repeat for a _very_ long while ... >
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: thin: 253:4: commit failed: error = -28
device-mapper: thin: 253:4: switching pool to read-only mode

after patch:

device-mapper: thin: 253:4: reached low water mark for metadata device: sending event.
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: thin: 253:4: no free metadata space available.
device-mapper: thin: 253:4: switching pool to read-only mode

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Cc: stable@vger.kernel.org

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 24327adc925c..44ee489f4a6e 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -959,7 +959,7 @@ static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
                  * table reload).
                  */
                 if (!free_blocks) {
-                        DMWARN("%s: no free space available.",
+                        DMWARN("%s: no free data space available.",
                                dm_device_name(pool->pool_md));
                         spin_lock_irqsave(&pool->lock, flags);
                         pool->no_free_space = 1;
@@ -969,8 +969,16 @@ static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
         }
 
         r = dm_pool_alloc_data_block(pool->pmd, result);
-        if (r)
+        if (r) {
+                if (r == -ENOSPC &&
+                    !dm_pool_get_free_metadata_block_count(pool->pmd, &free_blocks) &&
+                    !free_blocks) {
+                        DMWARN("%s: no free metadata space available.",
+                               dm_device_name(pool->pool_md));
+                        set_pool_mode(pool, PM_READ_ONLY);
+                }
                 return r;
+        }
 
         return 0;
 }