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

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Date:   Mon, 9 Apr 2018 21:30:11 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "ming.lei@...hat.com" <ming.lei@...hat.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>,
        "wakko@...mx.eu.org" <wakko@...mx.eu.org>
Subject: Re: 4.15.14 crash with iscsi target and dvd

On Sun, 2018-04-08 at 12:02 -0400, Wakko Warner wrote:
> 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);

Hello Ming,

Can you have a look at this? The start of this e-mail thread is available at
https://www.mail-archive.com/linux-scsi@vger.kernel.org/msg72574.html.

Thanks,

Bart.