Btrfs: rewrite btrfs_trim_block_group()

There are various bugs in block group trimming:

- It may trim from offset smaller than user-specified offset.
- It may trim beyond user-specified range.
- It may leak free space for extents smaller than specified minlen.
- It may truncate the last trimmed extent thus leak free space.
- With mixed extents+bitmaps, some extents may not be trimmed.
- With mixed extents+bitmaps, some bitmaps may not be trimmed (even
none will be trimmed). Even for those trimmed, not all the free space
in the bitmaps will be trimmed.

I rewrite btrfs_trim_block_group() and break it into two functions.
One is to trim extents only, and the other is to trim bitmaps only.

Before patching:

	# fstrim -v /mnt/
	/mnt/: 1496465408 bytes were trimmed

After patching:

	# fstrim -v /mnt/
	/mnt/: 2193768448 bytes were trimmed

And this matches the total free space:

	# btrfs fi df /mnt
	Data: total=3.58GB, used=1.79GB
	System, DUP: total=8.00MB, used=4.00KB
	System: total=4.00MB, used=0.00
	Metadata, DUP: total=205.12MB, used=97.14MB
	Metadata: total=8.00MB, used=0.00

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 164 insertions, 71 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index e4eb222147cc..b3cbb8939fa3 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -2594,17 +2594,57 @@ void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
         cluster->block_group = NULL;
 }
 
-int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
-                           u64 *trimmed, u64 start, u64 end, u64 minlen)
+static int do_trimming(struct btrfs_block_group_cache *block_group,
+                       u64 *total_trimmed, u64 start, u64 bytes,
+                       u64 reserved_start, u64 reserved_bytes)
 {
-        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
-        struct btrfs_free_space *entry = NULL;
+        struct btrfs_space_info *space_info = block_group->space_info;
         struct btrfs_fs_info *fs_info = block_group->fs_info;
-        u64 bytes = 0;
-        u64 actually_trimmed;
-        int ret = 0;
+        int ret;
+        int update = 0;
+        u64 trimmed = 0;
 
-        *trimmed = 0;
+        spin_lock(&space_info->lock);
+        spin_lock(&block_group->lock);
+        if (!block_group->ro) {
+                block_group->reserved += reserved_bytes;
+                space_info->bytes_reserved += reserved_bytes;
+                update = 1;
+        }
+        spin_unlock(&block_group->lock);
+        spin_unlock(&space_info->lock);
+
+        ret = btrfs_error_discard_extent(fs_info->extent_root,
+                                         start, bytes, &trimmed);
+        if (!ret)
+                *total_trimmed += trimmed;
+
+        btrfs_add_free_space(block_group, reserved_start, reserved_bytes);
+
+        if (update) {
+                spin_lock(&space_info->lock);
+                spin_lock(&block_group->lock);
+                if (block_group->ro)
+                        space_info->bytes_readonly += reserved_bytes;
+                block_group->reserved -= reserved_bytes;
+                space_info->bytes_reserved -= reserved_bytes;
+                spin_unlock(&space_info->lock);
+                spin_unlock(&block_group->lock);
+        }
+
+        return ret;
+}
+
+static int trim_no_bitmap(struct btrfs_block_group_cache *block_group,
+                          u64 *total_trimmed, u64 start, u64 end, u64 minlen)
+{
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
+        struct btrfs_free_space *entry;
+        struct rb_node *node;
+        int ret = 0;
+        u64 extent_start;
+        u64 extent_bytes;
+        u64 bytes;
 
         while (start < end) {
                 spin_lock(&ctl->tree_lock);
@@ -2615,81 +2655,118 @@ int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
                 }
 
                 entry = tree_search_offset(ctl, start, 0, 1);
-                if (!entry)
-                        entry = tree_search_offset(ctl,
-                                                   offset_to_bitmap(ctl, start),
-                                                   1, 1);
-
-                if (!entry || entry->offset >= end) {
+                if (!entry) {
                         spin_unlock(&ctl->tree_lock);
                         break;
                 }
 
-                if (entry->bitmap) {
-                        ret = search_bitmap(ctl, entry, &start, &bytes);
-                        if (!ret) {
-                                if (start >= end) {
-                                        spin_unlock(&ctl->tree_lock);
-                                        break;
-                                }
-                                bytes = min(bytes, end - start);
-                                bitmap_clear_bits(ctl, entry, start, bytes);
-                                if (entry->bytes == 0)
-                                        free_bitmap(ctl, entry);
-                        } else {
-                                start = entry->offset + BITS_PER_BITMAP *
-                                        block_group->sectorsize;
+                /* skip bitmaps */
+                while (entry->bitmap) {
+                        node = rb_next(&entry->offset_index);
+                        if (!node) {
                                 spin_unlock(&ctl->tree_lock);
-                                ret = 0;
-                                continue;
+                                goto out;
                         }
-                } else {
-                        start = entry->offset;
-                        bytes = min(entry->bytes, end - start);
-                        unlink_free_space(ctl, entry);
-                        kmem_cache_free(btrfs_free_space_cachep, entry);
+                        entry = rb_entry(node, struct btrfs_free_space,
+                                         offset_index);
+                }
+
+                if (entry->offset >= end) {
+                        spin_unlock(&ctl->tree_lock);
+                        break;
+                }
+
+                extent_start = entry->offset;
+                extent_bytes = entry->bytes;
+                start = max(start, extent_start);
+                bytes = min(extent_start + extent_bytes, end) - start;
+                if (bytes < minlen) {
+                        spin_unlock(&ctl->tree_lock);
+                        goto next;
                 }
 
+                unlink_free_space(ctl, entry);
+                kmem_cache_free(btrfs_free_space_cachep, entry);
+
                 spin_unlock(&ctl->tree_lock);
 
-                if (bytes >= minlen) {
-                        struct btrfs_space_info *space_info;
-                        int update = 0;
-
-                        space_info = block_group->space_info;
-                        spin_lock(&space_info->lock);
-                        spin_lock(&block_group->lock);
-                        if (!block_group->ro) {
-                                block_group->reserved += bytes;
-                                space_info->bytes_reserved += bytes;
-                                update = 1;
-                        }
-                        spin_unlock(&block_group->lock);
-                        spin_unlock(&space_info->lock);
-
-                        ret = btrfs_error_discard_extent(fs_info->extent_root,
-                                                         start,
-                                                         bytes,
-                                                         &actually_trimmed);
-
-                        btrfs_add_free_space(block_group, start, bytes);
-                        if (update) {
-                                spin_lock(&space_info->lock);
-                                spin_lock(&block_group->lock);
-                                if (block_group->ro)
-                                        space_info->bytes_readonly += bytes;
-                                block_group->reserved -= bytes;
-                                space_info->bytes_reserved -= bytes;
-                                spin_unlock(&space_info->lock);
-                                spin_unlock(&block_group->lock);
-                        }
+                ret = do_trimming(block_group, total_trimmed, start, bytes,
+                                  extent_start, extent_bytes);
+                if (ret)
+                        break;
+next:
+                start += bytes;
 
-                        if (ret)
-                                break;
-                        *trimmed += actually_trimmed;
+                if (fatal_signal_pending(current)) {
+                        ret = -ERESTARTSYS;
+                        break;
+                }
+
+                cond_resched();
+        }
+out:
+        return ret;
+}
+
+static int trim_bitmaps(struct btrfs_block_group_cache *block_group,
+                        u64 *total_trimmed, u64 start, u64 end, u64 minlen)
+{
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
+        struct btrfs_free_space *entry;
+        int ret = 0;
+        int ret2;
+        u64 bytes;
+        u64 offset = offset_to_bitmap(ctl, start);
+
+        while (offset < end) {
+                bool next_bitmap = false;
+
+                spin_lock(&ctl->tree_lock);
+
+                if (ctl->free_space < minlen) {
+                        spin_unlock(&ctl->tree_lock);
+                        break;
+                }
+
+                entry = tree_search_offset(ctl, offset, 1, 0);
+                if (!entry) {
+                        spin_unlock(&ctl->tree_lock);
+                        next_bitmap = true;
+                        goto next;
+                }
+
+                bytes = minlen;
+                ret2 = search_bitmap(ctl, entry, &start, &bytes);
+                if (ret2 || start >= end) {
+                        spin_unlock(&ctl->tree_lock);
+                        next_bitmap = true;
+                        goto next;
+                }
+
+                bytes = min(bytes, end - start);
+                if (bytes < minlen) {
+                        spin_unlock(&ctl->tree_lock);
+                        goto next;
+                }
+
+                bitmap_clear_bits(ctl, entry, start, bytes);
+                if (entry->bytes == 0)
+                        free_bitmap(ctl, entry);
+
+                spin_unlock(&ctl->tree_lock);
+
+                ret = do_trimming(block_group, total_trimmed, start, bytes,
+                                  start, bytes);
+                if (ret)
+                        break;
+next:
+                if (next_bitmap) {
+                        offset += BITS_PER_BITMAP * ctl->unit;
+                } else {
+                        start += bytes;
+                        if (start >= offset + BITS_PER_BITMAP * ctl->unit)
+                                offset += BITS_PER_BITMAP * ctl->unit;
                 }
-                start += bytes;
-                bytes = 0;
 
                 if (fatal_signal_pending(current)) {
                         ret = -ERESTARTSYS;
@@ -2702,6 +2779,22 @@ int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
         return ret;
 }
 
+int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
+                           u64 *trimmed, u64 start, u64 end, u64 minlen)
+{
+        int ret;
+
+        *trimmed = 0;
+
+        ret = trim_no_bitmap(block_group, trimmed, start, end, minlen);
+        if (ret)
+                return ret;
+
+        ret = trim_bitmaps(block_group, trimmed, start, end, minlen);
+
+        return ret;
+}
+
 /*
  * Find the left-most item in the cache tree, and then return the
  * smallest inode number in the item.