dm thin metadata: make dm_thin_find_mapped_range() atomic

Refactor dm_thin_find_mapped_range() so that it takes the read lock on
the metadata's lock; rather than relying on finer grained locking that
is pushed down inside dm_thin_find_next_mapped_block() and
dm_thin_find_block().

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 43 insertions, 21 deletions

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 7547315ff18a..f962d6453afd 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -1408,8 +1408,8 @@ static void unpack_lookup_result(struct dm_thin_device *td, __le64 value,
         result->shared = __snapshotted_since(td, exception_time);
 }
 
-int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
-                       int can_issue_io, struct dm_thin_lookup_result *result)
+static int __find_block(struct dm_thin_device *td, dm_block_t block,
+                        int can_issue_io, struct dm_thin_lookup_result *result)
 {
         int r;
         __le64 value;
@@ -1417,12 +1417,6 @@ int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
         dm_block_t keys[2] = { td->id, block };
         struct dm_btree_info *info;
 
-        down_read(&pmd->root_lock);
-        if (pmd->fail_io) {
-                up_read(&pmd->root_lock);
-                return -EINVAL;
-        }
-
         if (can_issue_io) {
                 info = &pmd->info;
         } else
@@ -1432,18 +1426,14 @@ int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
         if (!r)
                 unpack_lookup_result(td, value, result);
 
-        up_read(&pmd->root_lock);
         return r;
 }
 
-static int dm_thin_find_next_mapped_block(struct dm_thin_device *td, dm_block_t block,
-                                          dm_block_t *vblock,
-                                          struct dm_thin_lookup_result *result)
+int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
+                       int can_issue_io, struct dm_thin_lookup_result *result)
 {
         int r;
-        __le64 value;
         struct dm_pool_metadata *pmd = td->pmd;
-        dm_block_t keys[2] = { td->id, block };
 
         down_read(&pmd->root_lock);
         if (pmd->fail_io) {
@@ -1451,18 +1441,32 @@ static int dm_thin_find_next_mapped_block(struct dm_thin_device *td, dm_block_t
                 return -EINVAL;
         }
 
+        r = __find_block(td, block, can_issue_io, result);
+
+        up_read(&pmd->root_lock);
+        return r;
+}
+
+static int __find_next_mapped_block(struct dm_thin_device *td, dm_block_t block,
+                                          dm_block_t *vblock,
+                                          struct dm_thin_lookup_result *result)
+{
+        int r;
+        __le64 value;
+        struct dm_pool_metadata *pmd = td->pmd;
+        dm_block_t keys[2] = { td->id, block };
+
         r = dm_btree_lookup_next(&pmd->info, pmd->root, keys, vblock, &value);
         if (!r)
                 unpack_lookup_result(td, value, result);
 
-        up_read(&pmd->root_lock);
         return r;
 }
 
-int dm_thin_find_mapped_range(struct dm_thin_device *td,
-                              dm_block_t begin, dm_block_t end,
-                              dm_block_t *thin_begin, dm_block_t *thin_end,
-                              dm_block_t *pool_begin, bool *maybe_shared)
+static int __find_mapped_range(struct dm_thin_device *td,
+                               dm_block_t begin, dm_block_t end,
+                               dm_block_t *thin_begin, dm_block_t *thin_end,
+                               dm_block_t *pool_begin, bool *maybe_shared)
 {
         int r;
         dm_block_t pool_end;
@@ -1471,7 +1475,7 @@ int dm_thin_find_mapped_range(struct dm_thin_device *td,
         if (end < begin)
                 return -ENODATA;
 
-        r = dm_thin_find_next_mapped_block(td, begin, &begin, &lookup);
+        r = __find_next_mapped_block(td, begin, &begin, &lookup);
         if (r)
                 return r;
 
@@ -1485,7 +1489,7 @@ int dm_thin_find_mapped_range(struct dm_thin_device *td,
         begin++;
         pool_end = *pool_begin + 1;
         while (begin != end) {
-                r = dm_thin_find_block(td, begin, true, &lookup);
+                r = __find_block(td, begin, true, &lookup);
                 if (r) {
                         if (r == -ENODATA)
                                 break;
@@ -1505,6 +1509,24 @@ int dm_thin_find_mapped_range(struct dm_thin_device *td,
         return 0;
 }
 
+int dm_thin_find_mapped_range(struct dm_thin_device *td,
+                              dm_block_t begin, dm_block_t end,
+                              dm_block_t *thin_begin, dm_block_t *thin_end,
+                              dm_block_t *pool_begin, bool *maybe_shared)
+{
+        int r = -EINVAL;
+        struct dm_pool_metadata *pmd = td->pmd;
+
+        down_read(&pmd->root_lock);
+        if (!pmd->fail_io) {
+                r = __find_mapped_range(td, begin, end, thin_begin, thin_end,
+                                        pool_begin, maybe_shared);
+        }
+        up_read(&pmd->root_lock);
+
+        return r;
+}
+
 static int __insert(struct dm_thin_device *td, dm_block_t block,
                     dm_block_t data_block)
 {