Patch "btrfs: clear space cache inode generation always" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

btrfs: clear space cache inode generation always

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-clear-space-cache-inode-generation-always.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Josef Bacik <[email protected]>
Date: Fri, 17 Nov 2017 14:50:46 -0500
Subject: btrfs: clear space cache inode generation always

From: Josef Bacik <[email protected]>

commit 8e138e0d92c6c9d3d481674fb14e3439b495be37 upstream.

We discovered a box that had double allocations, and suspected the space cache may be to blame. While auditing the write out path I noticed that if we've already setup the space cache we will just carry on. This means that any error we hit after cache_save_setup before we go to actually write the cache out we won't reset the inode generation, so whatever was already written will be considered correct, except it'll be stale. Fix this by _always_ resetting the generation on the block group inode, this way we only ever have valid or invalid cache.

With this patch I was no longer able to reproduce cache corruption with dm-log-writes and my bpf error injection tool.

---
 fs/btrfs/extent-tree.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

@@ -3361,13 +3361,6 @@ again:
 		goto again;
 	}
 
-	/* We've already setup this transaction, go ahead and exit */
-	if (block_group->cache_generation == trans->transid &&
-	    i_size_read(inode)) {
-		dcs = BTRFS_DC_SETUP;
-		goto out_put;
-	}
-
 	/*
 	 * We want to set the generation to 0, that way if anything goes wrong
 	 * from here on out we know not to trust this cache when we load up next

@@ -3391,6 +3384,13 @@ again:
 	}
 	WARN_ON(ret);
 
+	/* We've already setup this transaction, go ahead and exit */
+	if (block_group->cache_generation == trans->transid &&
+	    i_size_read(inode)) {
+		dcs = BTRFS_DC_SETUP;
+		goto out_put;
+	}
+
 	if (i_size_read(inode) > 0) {
 		ret = btrfs_check_trunc_cache_free_space(root,
 					&root->fs_info->global_block_rsv);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/btrfs-clear-space-cache-inode-generation-always.patch