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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Filipe Manana <fdmanana@suse.com>,
        Anand Jain <anand.jain@oracle.com>,
        David Sterba <dsterba@suse.com>
Subject: [PATCH 4.9 010/128] Btrfs: do not abort transaction at btrfs_update_root() after failure to COW path
Date:   Wed, 29 May 2019 20:05:42 -0700
Message-Id: <20190530030435.413618973@linuxfoundation.org>
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From: Filipe Manana <fdmanana@suse.com>

commit 72bd2323ec87722c115a5906bc6a1b31d11e8f54 upstream.

Currently when we fail to COW a path at btrfs_update_root() we end up
always aborting the transaction. However all the current callers of
btrfs_update_root() are able to deal with errors returned from it, many do
end up aborting the transaction themselves (directly or not, such as the
transaction commit path), other BUG_ON() or just gracefully cancel whatever
they were doing.

When syncing the fsync log, we call btrfs_update_root() through
tree-log.c:update_log_root(), and if it returns an -ENOSPC error, the log
sync code does not abort the transaction, instead it gracefully handles
the error and returns -EAGAIN to the fsync handler, so that it falls back
to a transaction commit. Any other error different from -ENOSPC, makes the
log sync code abort the transaction.

So remove the transaction abort from btrfs_update_log() when we fail to
COW a path to update the root item, so that if an -ENOSPC failure happens
we avoid aborting the current transaction and have a chance of the fsync
succeeding after falling back to a transaction commit.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203413
Fixes: 79787eaab46121 ("btrfs: replace many BUG_ONs with proper error handling")
Cc: stable@vger.kernel.org # 4.4+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/btrfs/root-tree.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -144,10 +144,8 @@ int btrfs_update_root(struct btrfs_trans
 		return -ENOMEM;
 
 	ret = btrfs_search_slot(trans, root, key, path, 0, 1);
-	if (ret < 0) {
-		btrfs_abort_transaction(trans, ret);
+	if (ret < 0)
 		goto out;
-	}
 
 	if (ret != 0) {
 		btrfs_print_leaf(root, path->nodes[0]);