btrfs: Handle pending/pinned chunks before blockgroup relocation during device shrink

During device shrink pinned/pending chunks (i.e. those which have been
deleted/created respectively, in the current transaction and haven't
touched disk) need to be accounted when doing device shrink. Presently
this happens after the main relocation loop in btrfs_shrink_device,
which could lead to making another go in the body of the function.

Since there is no hard requirement to perform pinned/pending chunks
handling after the relocation loop, move the code before it. This leads
to simplifying the code flow around - i.e. no need to use 'goto again'.

A notable side effect of this change is that modification of the
device's size requires a transaction to be started and committed before
the relocation loop starts. This is necessary to ensure that relocation
process sees the shrunk device size.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 72e069c227ab3a6ebf52d85024152b4a8615009a..a64b76d93cf0d67bead0e46c99b4921febb4b6ab 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4720,15 +4720,16 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
        int slot;
        int failed = 0;
        bool retried = false;
-       bool checked_pending_chunks = false;
        struct extent_buffer *l;
        struct btrfs_key key;
        struct btrfs_super_block *super_copy = fs_info->super_copy;
        u64 old_total = btrfs_super_total_bytes(super_copy);
        u64 old_size = btrfs_device_get_total_bytes(device);
        u64 diff;
+       u64 start;
 
        new_size = round_down(new_size, fs_info->sectorsize);
+       start = new_size;
        diff = round_down(old_size - new_size, fs_info->sectorsize);
 
        if (test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
@@ -4740,6 +4741,12 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
 
        path->reada = READA_BACK;
 
+       trans = btrfs_start_transaction(root, 0);
+       if (IS_ERR(trans)) {
+               btrfs_free_path(path);
+               return PTR_ERR(trans);
+       }
+
        mutex_lock(&fs_info->chunk_mutex);
 
        btrfs_device_set_total_bytes(device, new_size);
@@ -4747,7 +4754,21 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
                device->fs_devices->total_rw_bytes -= diff;
                atomic64_sub(diff, &fs_info->free_chunk_space);
        }
-       mutex_unlock(&fs_info->chunk_mutex);
+
+       /*
+        * Once the device's size has been set to the new size, ensure all
+        * in-memory chunks are synced to disk so that the loop below sees them
+        * and relocates them accordingly.
+        */
+       if (contains_pending_extent(trans->transaction, device, &start, diff)) {
+               mutex_unlock(&fs_info->chunk_mutex);
+               ret = btrfs_commit_transaction(trans);
+               if (ret)
+                       goto done;
+       } else {
+               mutex_unlock(&fs_info->chunk_mutex);
+               btrfs_end_transaction(trans);
+       }
 
 again:
        key.objectid = device->devid;
@@ -4838,36 +4859,6 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
        }
 
        mutex_lock(&fs_info->chunk_mutex);
-
-       /*
-        * We checked in the above loop all device extents that were already in
-        * the device tree. However before we have updated the device's
-        * total_bytes to the new size, we might have had chunk allocations that
-        * have not complete yet (new block groups attached to transaction
-        * handles), and therefore their device extents were not yet in the
-        * device tree and we missed them in the loop above. So if we have any
-        * pending chunk using a device extent that overlaps the device range
-        * that we can not use anymore, commit the current transaction and
-        * repeat the search on the device tree - this way we guarantee we will
-        * not have chunks using device extents that end beyond 'new_size'.
-        */
-       if (!checked_pending_chunks) {
-               u64 start = new_size;
-               u64 len = old_size - new_size;
-
-               if (contains_pending_extent(trans->transaction, device,
-                                           &start, len)) {
-                       mutex_unlock(&fs_info->chunk_mutex);
-                       checked_pending_chunks = true;
-                       failed = 0;
-                       retried = false;
-                       ret = btrfs_commit_transaction(trans);
-                       if (ret)
-                               goto done;
-                       goto again;
-               }
-       }
-
        btrfs_device_set_disk_total_bytes(device, new_size);
        if (list_empty(&device->post_commit_list))
                list_add_tail(&device->post_commit_list,