[PATCH V2] Btrfs: disable online scrub repair on ro cases

[Liu Bo <bo.li.liu@oracle.com>]

This disables repair process on ro cases as it can cause system
to be unresponsive on the ASSERT() in repair_io_failure().

This can happen when scrub is running and a hardware error pops up,
we should fallback to ro mounts gracefully instead of being unresponsive.

Reported-by: Codebird <codebird@birds-are-nice.me>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
v2: Get @fs_info from a real pointer instead of a confusing-name u64 root.

 fs/btrfs/scrub.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 2907a77..cb8a4e0 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -682,11 +682,14 @@ static int scrub_fixup_readpage(u64 inum, u64 offset, u64 root, void *fixup_ctx)
 	struct btrfs_root *local_root;
 	int srcu_index;
 
+	fs_info = fixup->root->fs_info;
+	if (fs_info->sb->s_flags & MS_RDONLY)
+		return -EROFS;
+
 	key.objectid = root;
 	key.type = BTRFS_ROOT_ITEM_KEY;
 	key.offset = (u64)-1;
 
-	fs_info = fixup->root->fs_info;
 	srcu_index = srcu_read_lock(&fs_info->subvol_srcu);
 
 	local_root = btrfs_read_fs_root_no_name(fs_info, &key);
-- 
2.5.0