btrfs: update btrfs_space_info's bytes_may_use timely

This patch can fix some false ENOSPC errors, below test script can
reproduce one false ENOSPC error:
	#!/bin/bash
	dd if=/dev/zero of=fs.img bs=$((1024*1024)) count=128
	dev=$(losetup --show -f fs.img)
	mkfs.btrfs -f -M $dev
	mkdir /tmp/mntpoint
	mount $dev /tmp/mntpoint
	cd /tmp/mntpoint
	xfs_io -f -c "falloc 0 $((64*1024*1024))" testfile

Above script will fail for ENOSPC reason, but indeed fs still has free
space to satisfy this request. Please see call graph:
btrfs_fallocate()
|-> btrfs_alloc_data_chunk_ondemand()
|   bytes_may_use += 64M
|-> btrfs_prealloc_file_range()
    |-> btrfs_reserve_extent()
        |-> btrfs_add_reserved_bytes()
        |   alloc_type is RESERVE_ALLOC_NO_ACCOUNT, so it does not
        |   change bytes_may_use, and bytes_reserved += 64M. Now
        |   bytes_may_use + bytes_reserved == 128M, which is greater
        |   than btrfs_space_info's total_bytes, false enospc occurs.
        |   Note, the bytes_may_use decrease operation will be done in
        |   end of btrfs_fallocate(), which is too late.

Here is another simple case for buffered write:
                    CPU 1              |              CPU 2
                                       |
|-> cow_file_range()                   |-> __btrfs_buffered_write()
    |-> btrfs_reserve_extent()         |   |
    |                                  |   |
    |                                  |   |
    |    .....                         |   |-> btrfs_check_data_free_space()
    |                                  |
    |                                  |
    |-> extent_clear_unlock_delalloc() |

In CPU 1, btrfs_reserve_extent()->find_free_extent()->
btrfs_add_reserved_bytes() do not decrease bytes_may_use, the decrease
operation will be delayed to be done in extent_clear_unlock_delalloc().
Assume in this case, btrfs_reserve_extent() reserved 128MB data, CPU2's
btrfs_check_data_free_space() tries to reserve 100MB data space.
If
	100MB > data_sinfo->total_bytes - data_sinfo->bytes_used -
		data_sinfo->bytes_reserved - data_sinfo->bytes_pinned -
		data_sinfo->bytes_readonly - data_sinfo->bytes_may_use
btrfs_check_data_free_space() will try to allcate new data chunk or call
btrfs_start_delalloc_roots(), or commit current transaction in order to
reserve some free space, obviously a lot of work. But indeed it's not
necessary as long as decreasing bytes_may_use timely, we still have
free space, decreasing 128M from bytes_may_use.

To fix this issue, this patch chooses to update bytes_may_use for both
data and metadata in btrfs_add_reserved_bytes(). For compress path, real
extent length may not be equal to file content length, so introduce a
ram_bytes argument for btrfs_reserve_extent(), find_free_extent() and
btrfs_add_reserved_bytes(), it's becasue bytes_may_use is increased by
file content length. Then compress path can update bytes_may_use
correctly. Also now we can discard RESERVE_ALLOC_NO_ACCOUNT, RESERVE_ALLOC
and RESERVE_FREE.

As we know, usually EXTENT_DO_ACCOUNTING is used for error path. In
run_delalloc_nocow(), for inode marked as NODATACOW or extent marked as
PREALLOC, we also need to update bytes_may_use, but can not pass
EXTENT_DO_ACCOUNTING, because it also clears metadata reservation, so
here we introduce EXTENT_CLEAR_DATA_RESV flag to indicate btrfs_clear_bit_hook()
to update btrfs_space_info's bytes_may_use.

Meanwhile __btrfs_prealloc_file_range() will call
btrfs_free_reserved_data_space() internally for both sucessful and failed
path, btrfs_prealloc_file_range()'s callers does not need to call
btrfs_free_reserved_data_space() any more.

Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index acc6850a118f01213971d242306787583f9905b1..09cdff0d58e879cec6706a3856ec8b314cba6a92 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2579,7 +2579,7 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   u64 root_objectid, u64 owner, u64 offset,
                                   struct btrfs_key *ins);
-int btrfs_reserve_extent(struct btrfs_root *root, u64 num_bytes,
+int btrfs_reserve_extent(struct btrfs_root *root, u64 ram_bytes, u64 num_bytes,
                         u64 min_alloc_size, u64 empty_size, u64 hint_byte,
                         struct btrfs_key *ins, int is_data, int delalloc);
 int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index f1121db658785ef6d21e25e26411d17cf41b23b3..133c93b0a0f1d671e303a766e91135c744b8eeee 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -60,21 +60,6 @@ enum {
        CHUNK_ALLOC_FORCE = 2,
 };
 
-/*
- * Control how reservations are dealt with.
- *
- * RESERVE_FREE - freeing a reservation.
- * RESERVE_ALLOC - allocating space and we need to update bytes_may_use for
- *   ENOSPC accounting
- * RESERVE_ALLOC_NO_ACCOUNT - allocating space and we should not update
- *   bytes_may_use as the ENOSPC accounting is done elsewhere
- */
-enum {
-       RESERVE_FREE = 0,
-       RESERVE_ALLOC = 1,
-       RESERVE_ALLOC_NO_ACCOUNT = 2,
-};
-
 static int update_block_group(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root, u64 bytenr,
                              u64 num_bytes, int alloc);
@@ -105,7 +90,7 @@ static int find_next_key(struct btrfs_path *path, int level,
 static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
                            int dump_block_groups);
 static int btrfs_add_reserved_bytes(struct btrfs_block_group_cache *cache,
-                                   u64 num_bytes, int reserve, int delalloc);
+                                   u64 ram_bytes, u64 num_bytes, int delalloc);
 static int btrfs_free_reserved_bytes(struct btrfs_block_group_cache *cache,
                                     u64 num_bytes, int delalloc);
 static int block_rsv_use_bytes(struct btrfs_block_rsv *block_rsv,
@@ -3502,7 +3487,6 @@ again:
                dcs = BTRFS_DC_SETUP;
        else if (ret == -ENOSPC)
                set_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags);
-       btrfs_free_reserved_data_space(inode, 0, num_pages);
 
 out_put:
        iput(inode);
@@ -6500,8 +6484,9 @@ void btrfs_wait_block_group_reservations(struct btrfs_block_group_cache *bg)
 /**
  * btrfs_add_reserved_bytes - update the block_group and space info counters
  * @cache:     The cache we are manipulating
+ * @ram_bytes:  The number of bytes of file content, and will be same to
+ *              @num_bytes except for the compress path.
  * @num_bytes: The number of bytes in question
- * @reserve:   One of the reservation enums
  * @delalloc:   The blocks are allocated for the delalloc write
  *
  * This is called by the allocator when it reserves space. Metadata
@@ -6516,7 +6501,7 @@ void btrfs_wait_block_group_reservations(struct btrfs_block_group_cache *bg)
  * succeeds.
  */
 static int btrfs_add_reserved_bytes(struct btrfs_block_group_cache *cache,
-                                   u64 num_bytes, int reserve, int delalloc)
+                                   u64 ram_bytes, u64 num_bytes, int delalloc)
 {
        struct btrfs_space_info *space_info = cache->space_info;
        int ret = 0;
@@ -6528,13 +6513,11 @@ static int btrfs_add_reserved_bytes(struct btrfs_block_group_cache *cache,
        } else {
                cache->reserved += num_bytes;
                space_info->bytes_reserved += num_bytes;
-               if (reserve == RESERVE_ALLOC) {
-                       trace_btrfs_space_reservation(cache->fs_info,
-                                       "space_info", space_info->flags,
-                                       num_bytes, 0);
-                       space_info->bytes_may_use -= num_bytes;
-               }
 
+               trace_btrfs_space_reservation(cache->fs_info,
+                               "space_info", space_info->flags,
+                               ram_bytes, 0);
+               space_info->bytes_may_use -= ram_bytes;
                if (delalloc)
                        cache->delalloc_bytes += num_bytes;
        }
@@ -7433,9 +7416,9 @@ btrfs_release_block_group(struct btrfs_block_group_cache *cache,
  * the free space extent currently.
  */
 static noinline int find_free_extent(struct btrfs_root *orig_root,
-                                    u64 num_bytes, u64 empty_size,
-                                    u64 hint_byte, struct btrfs_key *ins,
-                                    u64 flags, int delalloc)
+                               u64 ram_bytes, u64 num_bytes, u64 empty_size,
+                               u64 hint_byte, struct btrfs_key *ins,
+                               u64 flags, int delalloc)
 {
        int ret = 0;
        struct btrfs_root *root = orig_root->fs_info->extent_root;
@@ -7447,8 +7430,6 @@ static noinline int find_free_extent(struct btrfs_root *orig_root,
        struct btrfs_space_info *space_info;
        int loop = 0;
        int index = __get_raid_index(flags);
-       int alloc_type = (flags & BTRFS_BLOCK_GROUP_DATA) ?
-               RESERVE_ALLOC_NO_ACCOUNT : RESERVE_ALLOC;
        bool failed_cluster_refill = false;
        bool failed_alloc = false;
        bool use_cluster = true;
@@ -7780,8 +7761,8 @@ checks:
                                             search_start - offset);
                BUG_ON(offset > search_start);
 
-               ret = btrfs_add_reserved_bytes(block_group, num_bytes,
-                               alloc_type, delalloc);
+               ret = btrfs_add_reserved_bytes(block_group, ram_bytes,
+                               num_bytes, delalloc);
                if (ret == -EAGAIN) {
                        btrfs_add_free_space(block_group, offset, num_bytes);
                        goto loop;
@@ -7953,7 +7934,7 @@ again:
        up_read(&info->groups_sem);
 }
 
-int btrfs_reserve_extent(struct btrfs_root *root,
+int btrfs_reserve_extent(struct btrfs_root *root, u64 ram_bytes,
                         u64 num_bytes, u64 min_alloc_size,
                         u64 empty_size, u64 hint_byte,
                         struct btrfs_key *ins, int is_data, int delalloc)
@@ -7965,8 +7946,8 @@ int btrfs_reserve_extent(struct btrfs_root *root,
        flags = btrfs_get_alloc_profile(root, is_data);
 again:
        WARN_ON(num_bytes < root->sectorsize);
-       ret = find_free_extent(root, num_bytes, empty_size, hint_byte, ins,
-                              flags, delalloc);
+       ret = find_free_extent(root, ram_bytes, num_bytes, empty_size,
+                              hint_byte, ins, flags, delalloc);
        if (!ret && !is_data) {
                btrfs_dec_block_group_reservations(root->fs_info,
                                                   ins->objectid);
@@ -7975,6 +7956,7 @@ again:
                        num_bytes = min(num_bytes >> 1, ins->offset);
                        num_bytes = round_down(num_bytes, root->sectorsize);
                        num_bytes = max(num_bytes, min_alloc_size);
+                       ram_bytes = num_bytes;
                        if (num_bytes == min_alloc_size)
                                final_tried = true;
                        goto again;
@@ -8241,7 +8223,7 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
                return -EINVAL;
 
        ret = btrfs_add_reserved_bytes(block_group, ins->offset,
-                       RESERVE_ALLOC_NO_ACCOUNT, 0);
+                                      ins->offset, 0);
        BUG_ON(ret); /* logic error */
        ret = alloc_reserved_file_extent(trans, root, 0, root_objectid,
                                         0, owner, offset, ins, 1);
@@ -8385,7 +8367,7 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
        if (IS_ERR(block_rsv))
                return ERR_CAST(block_rsv);
 
-       ret = btrfs_reserve_extent(root, blocksize, blocksize,
+       ret = btrfs_reserve_extent(root, blocksize, blocksize, blocksize,
                                   empty_size, hint, &ins, 0, 0);
        if (ret)
                goto out_unuse;

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index c0c1c4fef6cea0a6ab542a38596093b186b5d7d1..b52ca5db01cb99b456c74938178a91e0cd1fa408 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -20,6 +20,7 @@
 #define EXTENT_DAMAGED         (1U << 14)
 #define EXTENT_NORESERVE       (1U << 15)
 #define EXTENT_QGROUP_RESERVED (1U << 16)
+#define EXTENT_CLEAR_DATA_RESV (1U << 17)
 #define EXTENT_IOBITS          (EXTENT_LOCKED | EXTENT_WRITEBACK)
 #define EXTENT_CTLBITS         (EXTENT_DO_ACCOUNTING | EXTENT_FIRST_DELALLOC)
 

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 5842423f8f47b6a7146240c6b47ea1ead637f984..3391f2adf0c869466d47124461e62c2ee3bf3989 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2675,6 +2675,7 @@ static long btrfs_fallocate(struct file *file, int mode,
 
        alloc_start = round_down(offset, blocksize);
        alloc_end = round_up(offset + len, blocksize);
+       cur_offset = alloc_start;
 
        /* Make sure we aren't being give some crap mode */
        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
@@ -2767,7 +2768,6 @@ static long btrfs_fallocate(struct file *file, int mode,
 
        /* First, check if we exceed the qgroup limit */
        INIT_LIST_HEAD(&reserve_list);
-       cur_offset = alloc_start;
        while (1) {
                em = btrfs_get_extent(inode, NULL, 0, cur_offset,
                                      alloc_end - cur_offset, 0);
@@ -2794,6 +2794,14 @@ static long btrfs_fallocate(struct file *file, int mode,
                                        last_byte - cur_offset);
                        if (ret < 0)
                                break;
+               } else {
+                       /*
+                        * Do not need to reserve unwritten extent for this
+                        * range, free reserved data space first, otherwise
+                        * it'll result in false ENOSPC error.
+                        */
+                       btrfs_free_reserved_data_space(inode, cur_offset,
+                               last_byte - cur_offset);
                }
                free_extent_map(em);
                cur_offset = last_byte;
@@ -2811,6 +2819,9 @@ static long btrfs_fallocate(struct file *file, int mode,
                                        range->start,
                                        range->len, 1 << inode->i_blkbits,
                                        offset + len, &alloc_hint);
+               else
+                       btrfs_free_reserved_data_space(inode, range->start,
+                                                      range->len);
                list_del(&range->list);
                kfree(range);
        }
@@ -2845,18 +2856,11 @@ out_unlock:
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
                             &cached_state, GFP_KERNEL);
 out:
-       /*
-        * As we waited the extent range, the data_rsv_map must be empty
-        * in the range, as written data range will be released from it.
-        * And for prealloacted extent, it will also be released when
-        * its metadata is written.
-        * So this is completely used as cleanup.
-        */
-       btrfs_qgroup_free_data(inode, alloc_start, alloc_end - alloc_start);
        inode_unlock(inode);
        /* Let go of our reservation. */
-       btrfs_free_reserved_data_space(inode, alloc_start,
-                                      alloc_end - alloc_start);
+       if (ret != 0)
+               btrfs_free_reserved_data_space(inode, alloc_start,
+                                      alloc_end - cur_offset);
        return ret;
 }
 

diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c
index aa6fabaee72ed488844fc042e98536a77e9148cf..359ee861b5a4b90e567ca63477fd579055477e3f 100644 (file)
--- a/fs/btrfs/inode-map.c
+++ b/fs/btrfs/inode-map.c
@@ -495,10 +495,9 @@ again:
        ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, prealloc,
                                              prealloc, prealloc, &alloc_hint);
        if (ret) {
-               btrfs_delalloc_release_space(inode, 0, prealloc);
+               btrfs_delalloc_release_metadata(inode, prealloc);
                goto out_put;
        }
-       btrfs_free_reserved_data_space(inode, 0, prealloc);
 
        ret = btrfs_write_out_ino_cache(root, trans, path, inode);
 out_put:

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 29636624a42797388d25a9671f0c1440fe1bedbd..bcea20015d9acedf100a86f7ee56da24fa78323b 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -566,6 +566,8 @@ cont:
                                                     PAGE_SET_WRITEBACK |
                                                     page_error_op |
                                                     PAGE_END_WRITEBACK);
+                       btrfs_free_reserved_data_space_noquota(inode, start,
+                                               end - start + 1);
                        goto free_pages_out;
                }
        }
@@ -742,7 +744,7 @@ retry:
                lock_extent(io_tree, async_extent->start,
                            async_extent->start + async_extent->ram_size - 1);
 
-               ret = btrfs_reserve_extent(root,
+               ret = btrfs_reserve_extent(root, async_extent->ram_size,
                                           async_extent->compressed_size,
                                           async_extent->compressed_size,
                                           0, alloc_hint, &ins, 1, 1);
@@ -969,7 +971,8 @@ static noinline int cow_file_range(struct inode *inode,
                                     EXTENT_DEFRAG, PAGE_UNLOCK |
                                     PAGE_CLEAR_DIRTY | PAGE_SET_WRITEBACK |
                                     PAGE_END_WRITEBACK);
-
+                       btrfs_free_reserved_data_space_noquota(inode, start,
+                                               end - start + 1);
                        *nr_written = *nr_written +
                             (end - start + PAGE_SIZE) / PAGE_SIZE;
                        *page_started = 1;
@@ -989,7 +992,7 @@ static noinline int cow_file_range(struct inode *inode,
                unsigned long op;
 
                cur_alloc_size = disk_num_bytes;
-               ret = btrfs_reserve_extent(root, cur_alloc_size,
+               ret = btrfs_reserve_extent(root, cur_alloc_size, cur_alloc_size,
                                           root->sectorsize, 0, alloc_hint,
                                           &ins, 1, 1);
                if (ret < 0)
@@ -1489,8 +1492,10 @@ out_check:
                extent_clear_unlock_delalloc(inode, cur_offset,
                                             cur_offset + num_bytes - 1,
                                             locked_page, EXTENT_LOCKED |
-                                            EXTENT_DELALLOC, PAGE_UNLOCK |
-                                            PAGE_SET_PRIVATE2);
+                                            EXTENT_DELALLOC |
+                                            EXTENT_CLEAR_DATA_RESV,
+                                            PAGE_UNLOCK | PAGE_SET_PRIVATE2);
+
                if (!nolock && nocow)
                        btrfs_end_write_no_snapshoting(root);
                cur_offset = extent_end;
@@ -1807,7 +1812,9 @@ static void btrfs_clear_bit_hook(struct inode *inode,
                        return;
 
                if (root->root_key.objectid != BTRFS_DATA_RELOC_TREE_OBJECTID
-                   && do_list && !(state->state & EXTENT_NORESERVE))
+                   && do_list && !(state->state & EXTENT_NORESERVE)
+                   && (*bits & (EXTENT_DO_ACCOUNTING |
+                   EXTENT_CLEAR_DATA_RESV)))
                        btrfs_free_reserved_data_space_noquota(inode,
                                        state->start, len);
 
@@ -7252,7 +7259,7 @@ static struct extent_map *btrfs_new_extent_direct(struct inode *inode,
        int ret;
 
        alloc_hint = get_extent_allocation_hint(inode, start, len);
-       ret = btrfs_reserve_extent(root, len, root->sectorsize, 0,
+       ret = btrfs_reserve_extent(root, len, len, root->sectorsize, 0,
                                   alloc_hint, &ins, 1, 1);
        if (ret)
                return ERR_PTR(ret);
@@ -7752,6 +7759,13 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
                                ret = PTR_ERR(em2);
                                goto unlock_err;
                        }
+                       /*
+                        * For inode marked NODATACOW or extent marked PREALLOC,
+                        * use the existing or preallocated extent, so does not
+                        * need to adjust btrfs_space_info's bytes_may_use.
+                        */
+                       btrfs_free_reserved_data_space_noquota(inode,
+                                       start, len);
                        goto unlock;
                }
        }
@@ -7786,7 +7800,6 @@ unlock:
                        i_size_write(inode, start + len);
 
                adjust_dio_outstanding_extents(inode, dio_data, len);
-               btrfs_free_reserved_data_space(inode, start, len);
                WARN_ON(dio_data->reserve < len);
                dio_data->reserve -= len;
                dio_data->unsubmitted_oe_range_end = start + len;
@@ -10306,6 +10319,7 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
        u64 last_alloc = (u64)-1;
        int ret = 0;
        bool own_trans = true;
+       u64 end = start + num_bytes - 1;
 
        if (trans)
                own_trans = false;
@@ -10327,8 +10341,8 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
                 * sized chunks.
                 */
                cur_bytes = min(cur_bytes, last_alloc);
-               ret = btrfs_reserve_extent(root, cur_bytes, min_size, 0,
-                                          *alloc_hint, &ins, 1, 0);
+               ret = btrfs_reserve_extent(root, cur_bytes, cur_bytes,
+                               min_size, 0, *alloc_hint, &ins, 1, 0);
                if (ret) {
                        if (own_trans)
                                btrfs_end_transaction(trans, root);
@@ -10414,6 +10428,9 @@ next:
                if (own_trans)
                        btrfs_end_transaction(trans, root);
        }
+       if (cur_offset < end)
+               btrfs_free_reserved_data_space(inode, cur_offset,
+                       end - cur_offset + 1);
        return ret;
 }
 

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 71b4b70f56b950fb65cc4b806fd7bfed07edfa99..8a2c2a07987b2e02b6023428b4b931940baffc03 100644 (file)
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3040,6 +3040,7 @@ int prealloc_file_extent_cluster(struct inode *inode,
        int ret = 0;
        u64 prealloc_start = cluster->start - offset;
        u64 prealloc_end = cluster->end - offset;
+       u64 cur_offset;
 
        BUG_ON(cluster->start != cluster->boundary[0]);
        inode_lock(inode);
@@ -3049,6 +3050,7 @@ int prealloc_file_extent_cluster(struct inode *inode,
        if (ret)
                goto out;
 
+       cur_offset = prealloc_start;
        while (nr < cluster->nr) {
                start = cluster->boundary[nr] - offset;
                if (nr + 1 < cluster->nr)
@@ -3058,16 +3060,21 @@ int prealloc_file_extent_cluster(struct inode *inode,
 
                lock_extent(&BTRFS_I(inode)->io_tree, start, end);
                num_bytes = end + 1 - start;
+               if (cur_offset < start)
+                       btrfs_free_reserved_data_space(inode, cur_offset,
+                                       start - cur_offset);
                ret = btrfs_prealloc_file_range(inode, 0, start,
                                                num_bytes, num_bytes,
                                                end + 1, &alloc_hint);
+               cur_offset = end + 1;
                unlock_extent(&BTRFS_I(inode)->io_tree, start, end);
                if (ret)
                        break;
                nr++;
        }
-       btrfs_free_reserved_data_space(inode, prealloc_start,
-                                      prealloc_end + 1 - prealloc_start);
+       if (cur_offset < prealloc_end)
+               btrfs_free_reserved_data_space(inode, cur_offset,
+                                      prealloc_end + 1 - cur_offset);
 out:
        inode_unlock(inode);
        return ret;