queue-4.9/btrfs-do-not-abort-transaction-at-btrfs_update_root-after-failure-to-cow-path.patch

   1 From 72bd2323ec87722c115a5906bc6a1b31d11e8f54 Mon Sep 17 00:00:00 2001
   2 From: Filipe Manana <fdmanana@suse.com>
   3 Date: Mon, 29 Apr 2019 13:08:14 +0100
   4 Subject: Btrfs: do not abort transaction at btrfs_update_root() after failure to COW path
   5
   6 From: Filipe Manana <fdmanana@suse.com>
   7
   8 commit 72bd2323ec87722c115a5906bc6a1b31d11e8f54 upstream.
   9
  10 Currently when we fail to COW a path at btrfs_update_root() we end up
  11 always aborting the transaction. However all the current callers of
  12 btrfs_update_root() are able to deal with errors returned from it, many do
  13 end up aborting the transaction themselves (directly or not, such as the
  14 transaction commit path), other BUG_ON() or just gracefully cancel whatever
  15 they were doing.
  16
  17 When syncing the fsync log, we call btrfs_update_root() through
  18 tree-log.c:update_log_root(), and if it returns an -ENOSPC error, the log
  19 sync code does not abort the transaction, instead it gracefully handles
  20 the error and returns -EAGAIN to the fsync handler, so that it falls back
  21 to a transaction commit. Any other error different from -ENOSPC, makes the
  22 log sync code abort the transaction.
  23
  24 So remove the transaction abort from btrfs_update_log() when we fail to
  25 COW a path to update the root item, so that if an -ENOSPC failure happens
  26 we avoid aborting the current transaction and have a chance of the fsync
  27 succeeding after falling back to a transaction commit.
  28
  29 Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203413
  30 Fixes: 79787eaab46121 ("btrfs: replace many BUG_ONs with proper error handling")
  31 Cc: stable@vger.kernel.org # 4.4+
  32 Signed-off-by: Filipe Manana <fdmanana@suse.com>
  33 Reviewed-by: Anand Jain <anand.jain@oracle.com>
  34 Signed-off-by: David Sterba <dsterba@suse.com>
  35 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  36
  37 ---
  38  fs/btrfs/root-tree.c |    4 +---
  39  1 file changed, 1 insertion(+), 3 deletions(-)
  40
  41 --- a/fs/btrfs/root-tree.c
  42 +++ b/fs/btrfs/root-tree.c
  43 @@ -144,10 +144,8 @@ int btrfs_update_root(struct btrfs_trans
  44                 return -ENOMEM;
  45
  46         ret = btrfs_search_slot(trans, root, key, path, 0, 1);
  47 -       if (ret < 0) {
  48 -               btrfs_abort_transaction(trans, ret);
  49 +       if (ret < 0)
  50                 goto out;
  51 -       }
  52
  53         if (ret != 0) {
  54                 btrfs_print_leaf(root, path->nodes[0]);