[PATCH 2/2] btrfs: replace BUG_ON() in btrfs_csum_one_bio() with proper error handling

[Qu Wenruo <wqu@suse.com>]

The BUG_ON() in btrfs_csum_one_bio() means we're trying to submit a bio
while we don't have ordered extent for it at all.

Normally this won't happen and is indeed a code logical error.

But previous fix has already shown another possibility that, some call
sites don't handle error properly and submit the write bio after its
ordered extent has already been cleaned up.

This patch will add an extra safe net by replacing the BUG_ON() to
proper error handling.

And even if some day we hit a regression that we're submitting bio
without an ordered extent, we will return error and the pages will be
marked Error, and being caught properly.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/file-item.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 2673c6ba7a4e..25205b9dad69 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -665,7 +665,19 @@ blk_status_t btrfs_csum_one_bio(struct btrfs_inode *inode, struct bio *bio,
 
 		if (!ordered) {
 			ordered = btrfs_lookup_ordered_extent(inode, offset);
-			BUG_ON(!ordered); /* Logic error */
+			/*
+			 * No ordered extent mostly means the OE has been
+			 * removed (mostly for error handling). Normally for
+			 * such case we should not flush_write_bio(), but
+			 * end_write_bio().
+			 *
+			 * But an extra safe net will never hurt. Just error
+			 * out.
+			 */
+			if (unlikely(!ordered)) {
+				kvfree(sums);
+				return BLK_STS_IOERR;
+			}
 		}
 
 		nr_sectors = BTRFS_BYTES_TO_BLKS(fs_info,
-- 
2.32.0