So we start our freeze, somebody comes in and does an fsync() on a file
where we have to commit a transaction for whatever reason, and we will
deadlock because the freeze is waiting on FS_FREEZE people to stop writing
to the file system, but the transaction is waiting for its free space inodes
to be written out, which are in turn waiting on sb_start_intwrite while
trying to write the file extents. To fix this we'll just skip the
sb_start_intwrite() if we TRANS_JOIN_NOLOCK since we're being waited on by a
transaction commit so we're safe wrt to freeze and this will keep us from
deadlocking. Thanks,
Signed-off-by: Josef Bacik <jbacik@xxxxxxxxxxxx>
---
fs/btrfs/transaction.c | 10 +++++++++-
1 files changed, 9 insertions(+), 1 deletions(-)
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c9265a6..ba74dfb 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -342,7 +342,15 @@ again:
if (!h)
return ERR_PTR(-ENOMEM);
- if (!__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
+ /*
+ * If we are JOIN_NOLOCK we're already committing a transaction and
+ * waiting on this guy, so we don't need to do the sb_start_intwrite
+ * because we're already holding a ref. We need this because we could
+ * have raced in and did an fsync() on a file which can kick a commit
+ * and then we deadlock with somebody doing a freeze.
+ */
+ if (type != TRANS_JOIN_NOLOCK &&
+ !__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
if (type == TRANS_JOIN_FREEZE)
return ERR_PTR(-EPERM);
sb_start_intwrite(root->fs_info->sb);
--
1.7.7.6
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
