Btrfs: only map pages if we know we need them when reading the space cache

People have been running into a warning when loading space cache because the
page is already mapped when trying to read in a bitmap.  The way we read in
entries and pages is kind of convoluted, so fix it so that io_ctl_read_entry
maps the entries if it needs to, and if it hits the end of the page it simply
unmaps the page.  That way we can unconditionally unmap the io_ctl before
reading in the bitmap and we should stop hitting these warnings.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 7a15fcfb3e1f..181760f9d2ab 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -537,6 +537,13 @@ static int io_ctl_read_entry(struct io_ctl *io_ctl,
                             struct btrfs_free_space *entry, u8 *type)
 {
         struct btrfs_free_space_entry *e;
+        int ret;
+
+        if (!io_ctl->cur) {
+                ret = io_ctl_check_crc(io_ctl, io_ctl->index);
+                if (ret)
+                        return ret;
+        }
 
         e = io_ctl->cur;
         entry->offset = le64_to_cpu(e->offset);
@@ -550,10 +557,7 @@ static int io_ctl_read_entry(struct io_ctl *io_ctl,
 
         io_ctl_unmap_page(io_ctl);
 
-        if (io_ctl->index >= io_ctl->num_pages)
-                return 0;
-
-        return io_ctl_check_crc(io_ctl, io_ctl->index);
+        return 0;
 }
 
 static int io_ctl_read_bitmap(struct io_ctl *io_ctl,
@@ -561,9 +565,6 @@ static int io_ctl_read_bitmap(struct io_ctl *io_ctl,
 {
         int ret;
 
-        if (io_ctl->cur && io_ctl->cur != io_ctl->orig)
-                io_ctl_unmap_page(io_ctl);
-
         ret = io_ctl_check_crc(io_ctl, io_ctl->index);
         if (ret)
                 return ret;
@@ -699,6 +700,8 @@ int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
                 num_entries--;
         }
 
+        io_ctl_unmap_page(&io_ctl);
+
         /*
          * We add the bitmaps at the end of the entries in order that
          * the bitmap entries are added to the cache.