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

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Message-ID: <a631d319b0123a0f90b68e44a7df19dffb253751.camel@wdc.com>
Date:   Sat, 7 Apr 2018 02:06:39 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "wakko@...mx.eu.org" <wakko@...mx.eu.org>
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

On Fri, 2018-04-06 at 21:03 -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):
> > 
> > git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > git bisect start
> > git bisect bad v4.10
> > git bisect good v4.9
> > 
> > and then build the kernel, install it, boot the kernel and test it.
> > Depending on the result, run either git bisect bad or git bisect good and
> > keep going until git bisect comes to a conclusion. This can take an hour or
> > more.
> 
> I have 1 question.  Should make clean be done between tests?  My box
> compiles the whole kernel in 2 minutes.

If you trust that the build system will figure out all dependencies then
running make clean is not necessary. Personally I always run make clean
during a bisect before rebuilding the kernel because if a header file has
changed in e.g. the block layer a huge number of files has to be rebuilt
anyway.

Bart.