[PATCH 3/5] btrfs: only take normal tickets into account in may_commit_transaction

Josef Bacik
2020-03-09T20:23:33Z

In debugging a generic/320 failure on ppc64, Nikolay noticed that
sometimes we'd ENOSPC out with plenty of space to reclaim if we had
committed the transaction. He further discovered that this was because
there was a priority ticket that was small enough to fit in the free
space currently in the space_info. While that is a problem by itself,
it exposed another flaw, that we consider priority tickets in
may_commit_transaction.

Priority tickets are not allowed to commit the transaction, thus we
shouldn't even consider them in may_commit_transaction. Instead we need
to only consider current normal tickets. With this fix in place, we
will properly commit the transaction.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
fs/btrfs/space-info.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 8d00a9ee9458..d198cfd45cf7 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -592,10 +592,7 @@ static int may_commit_transaction(struct btrfs_fs_info *fs_info,
else
cur_free_bytes = 0;

- if (!list_empty(&space_info->priority_tickets))
- ticket = list_first_entry(&space_info->priority_tickets,
- struct reserve_ticket, list);
- else if (!list_empty(&space_info->tickets))
+ if (!list_empty(&space_info->tickets))
ticket = list_first_entry(&space_info->tickets,
struct reserve_ticket, list);
bytes_needed = (ticket) ? ticket->bytes : 0;
--
2.24.1