dm thin: always return -ENOSPC if no_free_space is set

If pool has 'no_free_space' set it means a previous allocation already determined the pool has no free space (and failed that allocation with -ENOSPC). By always returning -ENOSPC if 'no_free_space' is set, we do not allow the pool to oscillate between allocating blocks and then not. But a side-effect of this determinism is that if a user wants to be able to allocate new blocks they'll need to reload the pool's table (to clear the 'no_free_space' flag). This reload will happen automatically if the pool's data volume is resized. But if the user takes action to free a lot of space by deleting snapshot volumes, etc the pool will no longer allow data allocations to continue without an intervening table reload. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Acked-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>

dm thin: always return -ENOSPC if no_free_space is set
If pool has 'no_free_space' set it means a previous allocation already determined the pool has no free space (and failed that allocation with -ENOSPC). By always returning -ENOSPC if 'no_free_space' is set, we do not allow the pool to oscillate between allocating blocks and then not. But a side-effect of this determinism is that if a user wants to be able to allocate new blocks they'll need to reload the pool's table (to clear the 'no_free_space' flag). This reload will happen automatically if the pool's data volume is resized. But if the user takes action to free a lot of space by deleting snapshot volumes, etc the pool will no longer allow data allocations to continue without an intervening table reload. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Acked-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Mike Snitzer
1 parent f11c1c5693
Showing 1 changed file with 31 additions and 25 deletions Side-by-side Diff
drivers/md/dm-thin.c
@@ -918,6 +918,13 @@
 	unsigned long flags;
 	struct pool *pool = tc->pool;
  
+	/*
+	 * Once no_free_space is set we must not allow allocation to succeed.
+	 * Otherwise it is difficult to explain, debug, test and support.
+	 */
+	if (pool->no_free_space)
+		return -ENOSPC;
+
 	r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
 	if (r)
 		return r;
  
  
@@ -932,31 +939,30 @@
 	}
  
 	if (!free_blocks) {
-		if (pool->no_free_space)
-			return -ENOSPC;
-		else {
-			/*
-			 * Try to commit to see if that will free up some
-			 * more space.
-			 */
-			(void) commit_or_fallback(pool);
+		/*
+		 * Try to commit to see if that will free up some
+		 * more space.
+		 */
+		(void) commit_or_fallback(pool);
  
-			r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
-			if (r)
-				return r;
+		r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
+		if (r)
+			return r;
  
-			/*
-			 * If we still have no space we set a flag to avoid
-			 * doing all this checking and return -ENOSPC.
-			 */
-			if (!free_blocks) {
-				DMWARN("%s: no free space available.",
-				       dm_device_name(pool->pool_md));
-				spin_lock_irqsave(&pool->lock, flags);
-				pool->no_free_space = 1;
-				spin_unlock_irqrestore(&pool->lock, flags);
-				return -ENOSPC;
-			}
+		/*
+		 * If we still have no space we set a flag to avoid
+		 * doing all this checking and return -ENOSPC.  This
+		 * flag serves as a latch that disallows allocations from
+		 * this pool until the admin takes action (e.g. resize or
+		 * table reload).
+		 */
+		if (!free_blocks) {
+			DMWARN("%s: no free space available.",
+			       dm_device_name(pool->pool_md));
+			spin_lock_irqsave(&pool->lock, flags);
+			pool->no_free_space = 1;
+			spin_unlock_irqrestore(&pool->lock, flags);
+			return -ENOSPC;
 		}
 	}
  
@@ -2695,7 +2701,7 @@
 	.name = "thin-pool",
 	.features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
 		    DM_TARGET_IMMUTABLE,
-	.version = {1, 8, 0},
+	.version = {1, 9, 0},
 	.module = THIS_MODULE,
 	.ctr = pool_ctr,
 	.dtr = pool_dtr,
@@ -2982,7 +2988,7 @@
  
 static struct target_type thin_target = {
 	.name = "thin",
-	.version = {1, 8, 0},
+	.version = {1, 9, 0},
 	.module	= THIS_MODULE,
 	.ctr = thin_ctr,
 	.dtr = thin_dtr,
...	...	@@ -918,6 +918,13 @@
918	918	unsigned long flags;
919	919	struct pool *pool = tc->pool;
920	920
	921	+ /*
	922	+ * Once no_free_space is set we must not allow allocation to succeed.
	923	+ * Otherwise it is difficult to explain, debug, test and support.
	924	+ */
	925	+ if (pool->no_free_space)
	926	+ return -ENOSPC;
	927	+
921	928	r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
922	929	if (r)
923	930	return r;
924	931
925	932
...	...	@@ -932,31 +939,30 @@
932	939	}
933	940
934	941	if (!free_blocks) {
935		- if (pool->no_free_space)
936		- return -ENOSPC;
937		- else {
938		- /*
939		- * Try to commit to see if that will free up some
940		- * more space.
941		- */
942		- (void) commit_or_fallback(pool);
	942	+ /*
	943	+ * Try to commit to see if that will free up some
	944	+ * more space.
	945	+ */
	946	+ (void) commit_or_fallback(pool);
943	947
944		- r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
945		- if (r)
946		- return r;
	948	+ r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
	949	+ if (r)
	950	+ return r;
947	951
948		- /*
949		- * If we still have no space we set a flag to avoid
950		- * doing all this checking and return -ENOSPC.
951		- */
952		- if (!free_blocks) {
953		- DMWARN("%s: no free space available.",
954		- dm_device_name(pool->pool_md));
955		- spin_lock_irqsave(&pool->lock, flags);
956		- pool->no_free_space = 1;
957		- spin_unlock_irqrestore(&pool->lock, flags);
958		- return -ENOSPC;
959		- }
	952	+ /*
	953	+ * If we still have no space we set a flag to avoid
	954	+ * doing all this checking and return -ENOSPC. This
	955	+ * flag serves as a latch that disallows allocations from
	956	+ * this pool until the admin takes action (e.g. resize or
	957	+ * table reload).
	958	+ */
	959	+ if (!free_blocks) {
	960	+ DMWARN("%s: no free space available.",
	961	+ dm_device_name(pool->pool_md));
	962	+ spin_lock_irqsave(&pool->lock, flags);
	963	+ pool->no_free_space = 1;
	964	+ spin_unlock_irqrestore(&pool->lock, flags);
	965	+ return -ENOSPC;
960	966	}
961	967	}
962	968
...	...	@@ -2695,7 +2701,7 @@
2695	2701	.name = "thin-pool",
2696	2702	.features = DM_TARGET_SINGLETON \| DM_TARGET_ALWAYS_WRITEABLE \|
2697	2703	DM_TARGET_IMMUTABLE,
2698		- .version = {1, 8, 0},
	2704	+ .version = {1, 9, 0},
2699	2705	.module = THIS_MODULE,
2700	2706	.ctr = pool_ctr,
2701	2707	.dtr = pool_dtr,
...	...	@@ -2982,7 +2988,7 @@
2982	2988
2983	2989	static struct target_type thin_target = {
2984	2990	.name = "thin",
2985		- .version = {1, 8, 0},
	2991	+ .version = {1, 9, 0},
2986	2992	.module = THIS_MODULE,
2987	2993	.ctr = thin_ctr,
2988	2994	.dtr = thin_dtr,