@@ -49,6 +49,7 @@
#include "qgroup.h"
#include "delalloc-space.h"
#include "block-group.h"
+#include "space-info.h"
struct btrfs_iget_args {
struct btrfs_key *location;
@@ -1355,6 +1356,56 @@ static noinline int csum_exist_in_range(
return 1;
}
+static int fallback_to_cow(struct inode *inode, struct page *locked_page,
+ const u64 start, const u64 end,
+ int *page_started, unsigned long *nr_written)
+{
+ struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
+ u64 range_start = start;
+ u64 count;
+
+ /*
+ * If EXTENT_NORESERVE is set it means that when the buffered write was
+ * made we had not enough available data space and therefore we did not
+ * reserve data space for it, since we though we could do NOCOW for the
+ * respective file range (either there is prealloc extent or the inode
+ * has the NOCOW bit set).
+ *
+ * However when we need to fallback to COW mode (because for example the
+ * block group for the corresponding extent was turned to RO mode by a
+ * scrub or relocation) we need to do the following:
+ *
+ * 1) We increment the bytes_may_use counter of the data space info.
+ * If COW succeeds, it allocates a new data extent and after doing
+ * that it decrements the space info's bytes_may_use counter and
+ * increments its bytes_reserved counter by the same amount (we do
+ * this at btrfs_add_reserved_bytes()). So we need to increment the
+ * bytes_may_use counter to compensate (when space is reserved at
+ * buffered write time, the bytes_may_use counter is incremented);
+ *
+ * 2) We clear the EXTENT_NORESERVE bit from the range. We do this so
+ * that if the COW path fails for any reason, it decrements (through
+ * extent_clear_unlock_delalloc()) the bytes_may_use counter of the
+ * data space info, which we incremented in the step above.
+ */
+ count = count_range_bits(io_tree, &range_start, end, end + 1 - start,
+ EXTENT_NORESERVE, 0);
+ if (count > 0) {
+ struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
+ struct btrfs_space_info *sinfo = fs_info->data_sinfo;
+
+ spin_lock(&sinfo->lock);
+ btrfs_space_info_update_bytes_may_use(fs_info, sinfo, count);
+ spin_unlock(&sinfo->lock);
+
+ clear_extent_bit(io_tree, start, end, EXTENT_NORESERVE, 0, 0,
+ NULL);
+ }
+
+ return cow_file_range(inode, locked_page, start, end, page_started,
+ nr_written, 1);
+}
+
/*
* when nowcow writeback call back. This checks for snapshots or COW copies
* of the extents that exist in the file, and COWs the file as required.
@@ -1602,9 +1653,9 @@ out_check:
* NOCOW, following one which needs to be COW'ed
*/
if (cow_start != (u64)-1) {
- ret = cow_file_range(inode, locked_page,
- cow_start, found_key.offset - 1,
- page_started, nr_written, 1);
+ ret = fallback_to_cow(inode, locked_page, cow_start,
+ found_key.offset - 1,
+ page_started, nr_written);
if (ret) {
if (nocow)
btrfs_dec_nocow_writers(fs_info,
@@ -1693,8 +1744,8 @@ out_check:
if (cow_start != (u64)-1) {
cur_offset = end;
- ret = cow_file_range(inode, locked_page, cow_start, end,
- page_started, nr_written, 1);
+ ret = fallback_to_cow(inode, locked_page, cow_start, end,
+ page_started, nr_written);
if (ret)
goto error;
}