Set BLOCK_BIT_ERROR on bio submit failure during forced unmount

block_submit_bio will return -ENOLINK if called during a forced
shutdown, the bio is never submitted, and thus no completion callback
will fire to set BLOCK_BIT_ERROR. Any other task waiting for this
specific bp will end up waiting forever.

To fix, fall through to the existing block_end_io call on the
error path instead of returning directly.  That means moving
the forcing_unmount check past the setup calls so block_end_io's
bookkeeping stays balanced. block_end_io then sets BLOCK_BIT_ERROR
and wakes up waiters just as it would on a failed async completion.

Signed-off-by: Auke Kok <auke.kok@versity.com>

ReleaseNotes.md

@@ -1,23 +1,6 @@
 Versity ScoutFS Release Notes
 =============================
 
----
-v1.30
-\
-*Apr 21, 2026*
-
-Fix a problem reading the accumulated totals of contributing .totl.
-xattrs when log merging is in progress.  The problem would have readers
-of the totals calculate the sums incorrectly.
-
-Fix a problem updating quota rules.  There was a race where updates
-could be corrupted if they happened while a transaction was being
-written.
-
-Fix a problem deleting files with .indx. xattrs.  The internal indexing
-metadata wouldn't be properly deleted so the files would still claim to
-be present and visible in the index, though the file no longer existed.
-
 ---
 v1.29
 \

kmod/src/block.c

@@ -467,9 +467,6 @@ static int block_submit_bio(struct super_block *sb, struct block_private *bp,
 	sector_t sector;
 	int ret = 0;
 
-	if (scoutfs_forcing_unmount(sb))
-		return -ENOLINK;
-
 	sector = bp->bl.blkno << (SCOUTFS_BLOCK_LG_SHIFT - 9);
 
 	WARN_ON_ONCE(bp->bl.blkno == U64_MAX);
@@ -480,6 +477,17 @@ static int block_submit_bio(struct super_block *sb, struct block_private *bp,
 	set_bit(BLOCK_BIT_IO_BUSY, &bp->bits);
 	block_get(bp);
 
+	/*
+	 * A second thread may already be waiting on this block's completion
+	 * after this thread won the race to submit the block.  We exit through
+	 * the block_end_io error path which sets BLOCK_BIT_ERROR and assures
+	 * that other callers in the waitq get woken up.
+	 */
+	if (scoutfs_forcing_unmount(sb)) {
+		ret = -ENOLINK;
+		goto end_io;
+	}
+
 	blk_start_plug(&plug);
 
 	for (off = 0; off < SCOUTFS_BLOCK_LG_SIZE; off += PAGE_SIZE) {
@@ -517,6 +525,7 @@ static int block_submit_bio(struct super_block *sb, struct block_private *bp,
 
 	blk_finish_plug(&plug);
 
+end_io:
 	/* let racing end_io know we're done */
 	block_end_io(sb, opf, bp, ret);