Re: [PATCH 0/4] btrfs: reduce block group cache writeout times during commit

[Chris Mason <clm@fb.com>]

On Thu, Apr 23, 2015 at 02:05:48PM +0100, Filipe David Manana wrote:
> >> Trying the current integration-4.1 branch, I ran into the following
> >> during xfstests/btrfs/049:
> >>
> >
> > Ugh, I must not be waiting correctly in one of the inode cache writeout
> > sections.  But I've run 049 a whole bunch of times without triggering,
> > can you get this to happen consistently?
> 
> All the time so far.

I'm testing with this now:

commit 9f433238891b1b243c4f19d3f36eed913b270cbc
Author: Chris Mason <clm@fb.com>
Date:   Thu Apr 23 08:02:49 2015 -0700

    Btrfs: fix inode cache writeout
    
    The code to fix stalls during free spache cache IO wasn't using
    the correct root when waiting on the IO for inode caches.  This
    is only a problem when the inode cache is enabled with
    
    mount -o inode_cache
    
    This fixes the inode cache writeout to preserve any error values and
    makes sure not to override the root when inode cache writeout is done.
    
    Reported-by: Filipe Manana <fdmanana@suse.com>
    Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 5a4f5d1..8cd797f 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -1149,7 +1149,8 @@ int btrfs_wait_cache_io(struct btrfs_root *root,
 	if (!inode)
 		return 0;
 
-	root = root->fs_info->tree_root;
+	if (block_group)
+		root = root->fs_info->tree_root;
 
 	/* Flush the dirty pages in the cache file. */
 	ret = flush_dirty_cache(inode);
@@ -3465,9 +3466,12 @@ int btrfs_write_out_ino_cache(struct btrfs_root *root,
 	if (!btrfs_test_opt(root, INODE_MAP_CACHE))
 		return 0;
 
+	memset(&io_ctl, 0, sizeof(io_ctl));
 	ret = __btrfs_write_out_cache(root, inode, ctl, NULL, &io_ctl,
-				      trans, path, 0) ||
-		btrfs_wait_cache_io(root, trans, NULL, &io_ctl, path, 0);
+				      trans, path, 0);
+	if (!ret)
+		ret = btrfs_wait_cache_io(root, trans, NULL, &io_ctl, path, 0);
+
 	if (ret) {
 		btrfs_delalloc_release_metadata(inode, inode->i_size);
 #ifdef DEBUG