linux-kernel - Re: 4.15.14 crash with iscsi target and dvd

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Message-ID: <20180408161556.GB22869@animx.eu.org>
Date:   Sun, 8 Apr 2018 12:15:56 -0400
From:   Wakko Warner <wakko@...mx.eu.org>
To:     Bart Van Assche <Bart.VanAssche@....com>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "richard.weinberger@...il.com" <richard.weinberger@...il.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>
Subject: Re: 4.15.14 crash with iscsi target and dvd

Wakko Warner wrote:
> Bart Van Assche wrote:
> > 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@...il.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@....de>
>     Signed-off-by: Ming Lei <tom.leiming@...il.com>
>     Reviewed-by: Sagi Grimberg <sagi@...mberg.me>
>     Signed-off-by: Jens Axboe <axboe@...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.

One thing I noticed after doing this is errors in the kernel log on the
initiator:
[9072625.181744] sr 26:0:0:0: [sr1] tag#0 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[9072625.181802] sr 26:0:0:0: [sr1] tag#0 Sense Key : 0x2 [current] 
[9072625.181835] sr 26:0:0:0: [sr1] tag#0 ASC=0x8 ASCQ=0x0 
[9072625.181866] sr 26:0:0:0: [sr1] tag#0 CDB: opcode=0x28 28 00 00 0a 81 22 00 00 80 00
[9072625.181919] blk_update_request: I/O error, dev sr1, sector 2753672

When doing the exact same thing on the target, no mention.  My patch may not
be right, but it doesn't cause an oops.

I'm going to try 4.16.1 and see what happens.

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