Btrfs: check unused against how much space we actually want

There is a bug that may lead to early ENOSPC in our reservation code.  We've
been checking against num_bytes which may be above and beyond what we want to
actually reserve, which could give us a false ENOSPC.  Fix this by making sure
the unused space is above how much we want to reserve and not how much we're
trying to flush.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
(cherry picked from commit ef3be45722317f8c2fb0e861065df0c3830ff9ac)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a66a59c035a451d0bda180b48a0e159eebfc1e4e..de0d3e5d86d8325ee69cd501631b6dea47a9471e 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3472,7 +3472,7 @@ again:
         */
        if (unused <= space_info->total_bytes) {
                unused = space_info->total_bytes - unused;
-               if (unused >= num_bytes) {
+               if (unused >= orig_bytes) {
                        space_info->bytes_may_use += orig_bytes;
                        ret = 0;
                } else {