btrfs: Use ihold instead of igrab in cow_file_range_async

ihold is supposed to be used when the caller already has a reference to
the inode. In the case of cow_file_range_async this invariants holds,
since the 3 call chains leading to this function all take a reference:

btrfs_writepage  <--- does igrab
 extent_write_full_page
  __extent_writepage
   writepage_delalloc
     btrfs_run_delalloc_range
      cow_file_range_async

extent_write_cache_pages <--- does igrab
 __extent_writepage (same callchain as above)

and

submit_compressed_extents <-- already called from async CoW submit path,
			      which would have done ihold.
 extent_write_locked_range
  __extent_writepage

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ add comment ]
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3c11982..d548538 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1193,7 +1193,12 @@ static int cow_file_range_async(struct inode *inode, struct page *locked_page,
        while (start < end) {
                async_cow = kmalloc(sizeof(*async_cow), GFP_NOFS);
                BUG_ON(!async_cow); /* -ENOMEM */
-               async_cow->inode = igrab(inode);
+               /*
+                * igrab is called higher up in the call chain, take only the
+                * lightweight reference for the callback lifetime
+                */
+               ihold(inode);
+               async_cow->inode = inode;
                async_cow->fs_info = fs_info;
                async_cow->locked_page = locked_page;
                async_cow->start = start;