Btrfs: hold a ref on the inode during writepages

We can race with unlink and not actually be able to do our igrab in
btrfs_add_ordered_extent.  This will result in all sorts of problems.
Instead of doing the complicated work to try and handle returning an error
properly from btrfs_add_ordered_extent, just hold a ref to the inode during
writepages.  If we cannot grab a ref we know we're freeing this inode anyway
and can just drop the dirty pages on the floor, because screw them we're
going to invalidate them anyway.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index aaa12c1eb3483a8371df48e5765b986c436451c4..01c21b6c6d43e44a28a4c862ca6532d6f8b02654 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3324,6 +3324,7 @@ static int extent_write_cache_pages(struct extent_io_tree *tree,
                             writepage_t writepage, void *data,
                             void (*flush_fn)(void *))
 {
+       struct inode *inode = mapping->host;
        int ret = 0;
        int done = 0;
        int nr_to_write_done = 0;
@@ -3334,6 +3335,18 @@ static int extent_write_cache_pages(struct extent_io_tree *tree,
        int scanned = 0;
        int tag;
 
+       /*
+        * We have to hold onto the inode so that ordered extents can do their
+        * work when the IO finishes.  The alternative to this is failing to add
+        * an ordered extent if the igrab() fails there and that is a huge pain
+        * to deal with, so instead just hold onto the inode throughout the
+        * writepages operation.  If it fails here we are freeing up the inode
+        * anyway and we'd rather not waste our time writing out stuff that is
+        * going to be truncated anyway.
+        */
+       if (!igrab(inode))
+               return 0;
+
        pagevec_init(&pvec, 0);
        if (wbc->range_cyclic) {
                index = mapping->writeback_index; /* Start from prev offset */
@@ -3428,6 +3441,7 @@ retry:
                index = 0;
                goto retry;
        }
+       btrfs_add_delayed_iput(inode);
        return ret;
 }