Bart Van Assche wrote:

quoted

Have you tried to modify the kernel Makefile as indicated in the following
e-mail? This should make the kernel build:

https://lists.ubuntu.com/archives/kernel-team/2016-May/077178.html

Thanks.  That helped.

I finished with git bisect.  Here's the output:
84c8590646d5b35804bac60eb58b145839b5893e is the first bad commit
commit 84c8590646d5b35804bac60eb58b145839b5893e
Author: Ming Lei [off-list ref]
Date:   Fri Nov 11 20:05:32 2016 +0800

    target: avoid accessing .bi_vcnt directly
    
    When the bio is full, bio_add_pc_page() will return zero,
    so use this information tell when the bio is full.
    
    Also replace access to .bi_vcnt for pr_debug() with bio_segments().
    
    Reviewed-by: Christoph Hellwig [off-list ref]
    Signed-off-by: Ming Lei [off-list ref]
    Reviewed-by: Sagi Grimberg [off-list ref]
    Signed-off-by: Jens Axboe [off-list ref]

:040000 040000 a3ebbb71c52ee4eb8c3be4d033b81179211bf704 de39a328dbd1b18519946b3ad46d9302886e0dd0 M      drivers

I did a diff between HEAD^ and HEAD and manually patched the file from
4.15.14.  It's not an exact revert.  I'm running it now and it's working.
I'll do a better test later on.  Here's the patch:

--- a/drivers/target/target_core_pscsi.c	2018-02-04 14:31:31.077316617 -0500
+++ b/drivers/target/target_core_pscsi.c	2018-04-08 11:43:49.588641374 -0400

@@ -915,7 +915,9 @@
 					bio, page, bytes, off);
 			pr_debug("PSCSI: bio->bi_vcnt: %d nr_vecs: %d\n",
 				bio_segments(bio), nr_vecs);
-			if (rc != bytes) {
+			if (rc != bytes)
+				goto fail;
+			if (bio->bi_vcnt > nr_vecs) {
 				pr_debug("PSCSI: Reached bio->bi_vcnt max:"
 					" %d i: %d bio: %p, allocating another"
 					" bio\n", bio->bi_vcnt, i, bio);

I really appreciate your time and assistance with this.