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SubjectRe: 4.15.14 crash with iscsi target and dvd
Bart Van Assche wrote:
> On Sat, 2018-04-07 at 12:53 -0400, Wakko Warner wrote:
> > Bart Van Assche wrote:
> > > On Thu, 2018-04-05 at 22:06 -0400, Wakko Warner wrote:
> > > > I know now why scsi_print_command isn't doing anything. cmd->cmnd is null.
> > > > I added a dev_printk in scsi_print_command where the 2 if statements return.
> > > > Logs:
> > > > [ 29.866415] sr 3:0:0:0: cmd->cmnd is NULL
> > >
> > > That's something that should never happen. As one can see in
> > > scsi_setup_scsi_cmnd() and scsi_setup_fs_cmnd() both functions initialize
> > > that pointer. Since I have not yet been able to reproduce myself what you
> > > reported, would it be possible for you to bisect this issue? You will need
> > > to follow something like the following procedure (see also
> > > https://git-scm.com/docs/git-bisect):
> >
> > After doing 3 successful compiles with good/bad, I got this error and was
> > not able to compile any more kernels:
> > CC scripts/mod/devicetable-offsets.s
> > scripts/mod/empty.c:1:0: error: code model kernel does not support PIC mode
> > /* empty file to figure out endianness / word size */
> >
> > scripts/mod/devicetable-offsets.c:1:0: error: code model kernel does not support PIC mode
> > #include <linux/kbuild.h>
> >
> > scripts/Makefile.build:153: recipe for target 'scripts/mod/devicetable-offsets.s' failed
> >
> > I don't think it found the bad commit.
>
> 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 <tom.leiming@gmail.com>
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 <hch@lst.de>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@fb.com>

: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.

--
Microsoft has beaten Volkswagen's world record. Volkswagen only created 22
million bugs.

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